Deep Water: From the Frilled Shark to the Dumbo Octopus and from the Continental Shelf to the Mariana Trench [1 ed.] 0226827313, 9780226827315

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DEEP WATER

The University of Chicago Press, Chicago 60637 Text © 2023 by Welbeck Non-Fiction Limited Design © 2023 by Welbeck Non-Fiction Limited All rights reserved. No part of this book may be used or reproduced in any manner whatsoever without written permission, except in the case of brief quotations in critical articles and reviews. For more information, contact the University of Chicago Press, 1427 E. 60th St., Chicago, IL 60637. Published 2023 Printed in Dubai 32 31 30 29 28 27 26 25 24 23 1 2 3 4 5 ISBN-13: 978-0-226-82731-5 (cloth) ISBN-13: 978-0-226-82733-9 (e-book) DOI: https://doi.org/10.7208/chicago/9780226827339.001.0001 First published in 2023 by Welbeck An imprint of Welbeck Non-Fiction Limited part of Welbeck Publishing Group Offices in: London – 20 Mortimer Street, London W1T 3JW & Sydney – Level 17, 207 Kent St, Sydney NSW 2000 Australia www.welbeckpublishing.com Library of Congress Cataloging-in-Publication Data Names: Black, Riley, author. Title: Deep water : from the frilled shark to the dumbo octopus and from the continental shelf to the Mariana Trench / Riley Black. Description: Chicago : The University of Chicago Press, 2023. | Includes index. Identifiers:

LCCN

2022055946

|

ISBN

9780226827315

(cloth)

|

ISBN

9780226827339 (ebook) Subjects: LCSH: Deep-sea biology. | Marine ecology. Classification: LCC QH91.8.D44 B53 2023 | DDC 578.77/9--dc23/eng/20230126 LC record available at https://lccn.loc.gov/2022055946 Editorial: Isabel Wilkinson, Alison Moss Design: Russell Knowles, James Pople Picture Research: Steve Behan Production: Marion Storz

DEEP WATER From the Frilled Shark to the Dumbo Octopus and from the Continental Shelf to the Mariana Trench

riley black

The University of Chicago Press

Contents

• •• ••

Timeline of Discovery

6

Introduction 8

I !

•• •• •• •• •• •• •• •• •• ••

Zones of the Ocean

12

How Much of the Deep Sea is Unexplored?

16

Nutrient Cycling

20

Bioluminescence 26 Frilled Shark

32

Biogenic Sediment

36

Megamouth Shark

40

Coelacanths 44 Azoic Hypothesis

50

Cambrian Creatures

52

Giant Spider Crab

58

Ophthalmosaurus 62 Vampire Squid

66

Nautilus 70 Stromatolites 74 Bathysphere 80 Diel Vertical Migration

84

Goblin Shark

88

Giant Squid

92

Cookie-Cutter Shark

98

Giant Oarfish

100

Lanternfish

104

Big Red Jelly

108

Viperfish

110

Whalefalls 114

•• •• •• •• •• •• •• •• •• •• •' • •• • !

!

Hagfish

118

Gulper Eels

122

Orange Roughy

126

Brachiopods 128 Anglerfish

132

Hydrothermal Vents

136

Yeti Crabs

140

Methanogenic Bacteria

142

Giant Tube Worms

144

Chimaeras 148 Blubber 152 Cuvier’s Beaked Whale

156

Paleodictyon 160 Foraminiferans 164 DSV Alvin 168 Abyssal Plain

174

Sea Squirts

176

Sea Spiders

182

Dumbo Octopus

186

Giant Isopods

192

HMS Challenger 196 Crinoids 202 Trieste 208 Mariana Trench

212

i

Glossary 216 Index 218 Picture Credits

223

Timeline of Discovery 1817

1884

Diel vertical migration discovered in Daphnia.

Dumbo octopus described by naturalists.

1836

1898

Giant spider crab described by naturalists.

Goblin shark discovered off Japan.

1843

1898–99

Azoic hypothesis proposed by Edward Forbes.

Vampire squid discovered off Africa.

1850

1934

Fossil Paleodictyon described.

Record-breaking dive by the Bathysphere off Bermuda.

1857

1938

Giant squid named by Japetus Steenstrup.

Coelacanth caught and identified off South Africa.

1872–76

1960

Voyage of HMS Challenger.

Trieste dives into the Challenger Deep.

1879

1963

Giant isopods described by researchers.

Feeding behaviour of the cookie-cutter shark discovered.

1884

1965

Frilled shark caught in Japan’s Sagami Bay.

First deep dive of DSV Alvin.

i

•

6

TIMELINE OF DISCOVERY

1976

2006

The first known megamouth shark caught off Hawaii.

Yeti crab Kiwa named from hydrothermal vent communities.

1977

2014

Hydrothermal vents discovered off the Galapagos Islands.

Deepest dive by Cuvier’s beaked whale recorded.

1981

2018

Riftia tube worms named by scientists.

Deep-sea stromatolites discovered in the Arabian Sea.

1987

2018

Whalefall ecosystem discovered off California.

Blubber discovered in fossil ichthyosaurs.

1997

2019

Second coelacanth species found in Indonesia.

“Tethered” sea squirt species discovered in Java Trench.

2003

2020

Tiburonia granrojo jellyfish named by scientists.

Methane-eating bacteria found in the Pacific.

2003 Living Paleodictyon discovered on Mid-Atlantic Ridge.

2005 The first photographs taken of a giant squid in its natural habitat.

7

Introduction ........................ ................ ................ ....................... ................ .................. ..................... ................ .................. ...... .............. ................ .................. ..................... ................ ....................... ................ ................ ...

We live on an alien planet. That might seem like a strange sentiment given that our species evolved on Earth and it’s our only home in the universe. But even though we’ve set foot on the moon, sent satellites into space, and considered habitation on Mars, the fact of the matter is that we barely know our home planet at all.

W

hen Looked at from space only about 30 per cent of the

Zone at 1,000 metres (3,280 feet) to the deepest part of the

surface of our planet is land. The rest is water, and those

Mariana Trench. Whales and other creatures dive deep to feed

waters run very deep. Beyond the fringes of continental shelf that

on organisms that dwell in darkness, returning those nutrients

jut from the edges of the world’s land masses, the Earth’s crust

back near the surface in their bodily excretions. This effluvium

goes deeper and deeper, ultimately reaching cold and crushing

provides sustenance for plankton, and many of those plankton

depths at 10,984 metres (36,037 feet).

eventually drift downwards to become part of the ever-shifting

Our everyday world is not typical of life on Earth; if anything,

ocean floor. The deep sea is also part of our global carbon cycle

it’s the surface environment that’s strange. Most of the planet

that is changing because of human-created greenhouse gases.

is made up of deep-ocean habitats that are home to isopods

Carbon dioxide, methane, and other gases from the atmosphere

larger than a football, devilish-looking squid that feed on

are taken up by the upper layers of the ocean and used by

plankton, sharks that migrate up and down the water column

photosynthetic plankton and creatures to make their shells. Vast

on a daily cycle to follow the microorganisms they feed on, and

numbers of these organisms sink deep to the bottom when they

burbling vents surrounded by enormous worms that together

perish, piling up as sediments that eventually are compressed into

might offer a hint at how life on our planet got its start. Most

rock and effectively bury the carbon, among other elements, they

life on the planet is adapted to living in cold, dark conditions

took up. Even if you never visit the deep waters below 200 metres

where the only lights are the ones created by the organisms

(656 feet), you’re still directly connected to it.

that live there. And yet we are inextricably connected to these mysterious

Opposite Coral reefs often form in the Photic Zone, or the uppermost layers of the seas, where sunlight penetrates.

and expansive habitats, from the boundary of the Twilight

8

9

10

INTRODUCTION

Our knowledge of the deep is still in its infancy. Despite all the

But we are learning more. Every dive and every deep-sea

innovations and technical breakthroughs in studying the oceans

creature that washes ashore tells us something new. What follows

during the last 200 years, it’s only very recently that we’ve been

in this book is a selection of snapshots – creatures, concepts and

able to visit the deep ocean. Even when explorers visit the furthest

environments – that have altered our understanding of Earth’s

reaches, like the Challenger Deep, they are only able to stay for a

natural history. Some were named centuries ago but have only

matter of minutes due to the immense pressure. It was only about

recently been understood. Others are new discoveries that have

150 years ago that marine scientists realized that there is life to

shaken up what researchers previously assumed. All are part of

study below our familiar upper layers, and it’s been less than 100

a story that we are just starting to piece together. As you peruse

years since experts started to view the expansive abyssal plains –

each chapter, wondering over the behaviour of lanternfish or

about half of the Earth’s entire surface – as more than underwater

the biology of giant squid, remember this – all these organisms

deserts. Even when experts go searching, they are not always sure

and environments are sharing our planet, right now, clothed in

what they are actually looking at. It can take years for researchers

a deep darkness, their lives unfolding unseen in places that we

to recognize that a striking jellyfish or fuzzy-looking crab is

can only briefly visit.

something no one has ever seen before. The fossil record of the deep sea is even more mysterious. Rocks that preserve life in deep

Opposite Oceans cover about 70 per cent of the Earth’s surface and contain over 90 per cent of the world’s water, making ours the “Blue Planet”.

habitats are very rare – partly because the deep sea is constantly creating new rock and recycling old rock – and so investigating

Above Phytoplankton form the basis of marine ecosystems. These photosynthesizing microbes are the foundation for food webs from the surface to the deep sea.

this area is like trying to understand the history of life on our planet through a battered flipbook missing most of its pages.

11

Zones of the Ocean Look at the world around you. The surface of the Earth is covered with mountains and valleys, plains and plateaux, from continental depressions over 400 metres (1,312 feet) below sea level to mountain peaks that reach over 8,800 metres (28,870 feet) in the air. And yet all of this, the entirety of Earth’s terrestrial topography, could easily be subsumed by the sea.

T

he Mariana Trench is deeper than Mount Everest is tall by

to the lower depths, but migrate up and down in the water column

thousands of metres/feet. As striking as they are, the world’s

in search of food, light and mates. Nature does not fit neatly into

continents only make up about 30 per cent of the Earth’s surface.

boxes. Nevertheless, if we are to explore the deep sea, it’s worth

There is far more ocean – and deep ocean – than there is land, and

taking a moment to consider what deep truly means.

the mysteries of these depths have led us to wonder “What’s down there?” for century upon century. To humans, the deep sea may

Above Advanced SCUBA divers can descend to 40 metres (131 feet).

as well be another planet – a strange and even hostile place that

Opposite above The Great Barrier Reef, off the east coast of Queensland in Australia, lies in the Photic Zone.

requires special equipment to visit for even a few moments. The ocean is constantly changing. Even the organisms that live

Opposite below Oceanographers generally recognize five major ocean zones, from the surface to the world’s deepest trenches.

within the deep sea, as we’ll learn, do not always remain confined

12

ZONES OF THE OCEAN

ft

'

656

• m

Continental Shelf

Epipelagic Zone – The Sunlight Zone Mesopelagic Zone – The Twilight Zone

3000 6600 Continental Slope

Sperm whale maximum depth 3,300ft / 1,000m

1000 2000

Bathypelagic Zone – The Midnight Zone

3000

9900 13100 16300

200

Continental Rise

Depth at which RMS Titanic rests 12,500ft / 3,800m

19700

4000 Abyssopelagic Zone – The Abyss

5000

Ocean Basin

6000 7000

23000 26300

Hadal Zone – The Trenches

29600 32800

Depth James Cameron reached 35,756ft / 10,898m

8000 Height of Mount Everest 29,028ft / 8,848m

9000 10000 11000

36100

13

Oceanographers and marine scientists often divide the oceans

The Sunlight Zone (Epipelagic Zone) comprises the top 200

into five major zones, each with subdivisions within them.

metres (656 feet) of the ocean. A great deal of ocean biodiversity

It’s also worth noting that these divisions are primarily

– from plankton to great toothy sharks – lives in this top layer.

applied to parts of the oceans that are away from the coasts,

This top layer receives by far the most sunlight, which provides

beyond the continental shelves that skirt the edges of Earth’s

the raw energy photosynthesizing plankton need to make food

land masses. While both the coast and the open sea have a

and support so many of the oceans’ food webs.

Photic Zone – the depths where light is still visible – the

Sunlight begins to fade with depth. In fact, the Sunlight Zone

terminology for the deeper parts of the seas only come into play

is the shallowest of them all. At this zone’s deepest extent, only

beyond the nearshore environments that experts know as the

about 1 per cent of the available sunlight is still visible. Little

Neritic Zone.

wonder that oceanographers consider this the border with the next ocean division – the Twilight Zone.

So let’s say that you’re on a boat far from shore, on the open ocean beyond the reach of the continental shelf. Below you are

Technically called the Mesopelagic Zone, the Twilight Zone

five major ocean zones that correspond to increasing depths.

extends 200 to 1,000 metres (656–3,280 feet) below the ocean

Each has technical terms that may be used interchangeably or to

surface. Many famous deep-sea creatures live in this zone, from

emphasize a certain aspect of the depth, so to keep things simple

jellyfish that light up with bioluminescent colours to the still-

we can call them by their common names.

mysterious giant squid. Comprising about 20 per cent of the entire

14

ZONES OF THE OCEAN

oceans’ volume, this is the part of the seas that we often think of

Zone (Abyssopelagic Zone). The comparatively few organisms

– a dark place where remote operated vehicles (ROV) shine their

that live here exist in total darkness. Temperatures are about

lights on otherworldly invertebrates and snaggle-toothed fish.

2°C (35°F) and the very bottom waters are often so depleted in

Yet the Twilight Zone is not particularly deep in the context

oxygen that nothing can live there. Creatures that manage to

of the oceans’ entire depths. Below this zone, from 1,000 to

survive in this hostile place tend to be so adapted to the cold,

4,000 metres (3,280–13,123 feet) underneath the surface, is the

dark and pressure that they can’t survive in the oceans’ upper

Midnight Zone. Known as the Bathypelagic Zone to specialists,

zones, and many feed on the detritus – or “marine snow” – that

sunlight is not even a glimmer here. It’s also incredibly cold. The

falls from above.

average temperature remains about 4°C (39°F), with all the weight

Below that, at depths greater than 6,000 metres (19,685 feet),

of the overlying water creating incredible pressure. And without

lies the Hadal Zone (Hadalpelagic Zone) - the deepest reaches of

sunlight, there is no photosynthesis. The organisms that live here

the sea that can only be accessed by venturing into ocean trenches.

must either feed themselves by consuming other organisms or by an alternative energy pathway called chemosynthesis – turning

Opposite Remote operated vehicles – or ROVs – have been essential for exploring and mapping the seas.

molecules such as carbon dioxide and methane into energy. The ocean goes deeper still. Below the Midnight Zone, from

Above Jellyfish can be found from the oceans’ surface to over 3,700 metres (12,139 feet) down.

4,000 to 6,000 metres (13,123–19,685 feet) down, is the Abyssal

15

How Much of the Deep Sea is Unexplored? ........................ ................ ................ ....................... ................ .................. ..................... ................ .................. ...... .............. ................ .................. ..................... ................ ....................... ................ ................ ...

in The deep sea, The dark, the chill and the pressure present challenges for all forms of life – not least to ourselves. Yet, as oceanographer William Beebe once wrote, “One thing we cannot escape – forever afterward, throughout all our life, the memory of the magic of water and its life, of the home which was once our own – this will never leave us.” We are fascinated by what is down there, and what precious little we know drives our curiosity still further.

A

ccording to the United States National Oceanic and

back to the surface. Another estimate proposes that up to 91 per

Atmospheric Administration (NOAA), more than 80 per

cent of the species that live in the oceans are undescribed and have never been seen.

cent of the world’s seas are uncharted. That estimate might seem shockingly high, but makes sense when you look below

Even though the oceans have been a critical part of our planet

the surface. Even though humans have been travelling across

for billions of years, we have only just begun to visit and study

the ocean for thousands of years, much of what we know comes

them. It wasn’t until 1930, when naturalists William Beebe and

from areas close to shore or relevant to our travels between land

Otis Barton were lowered to a depth of 435 metres (1,427 feet),

masses. We know even less about the oceans below the surface

that anyone even saw the deep ocean with their own eyes (see

waters, into the dark Twilight Zone and below.

pages 80–83). That is less than 100 years of exploration and innovation as we’ve tried to dive deep.

So far, NOAA estimates, only about 10 per cent of the world’s seafloor has been mapped with modern sonar methods. And

Naturally, submersibles like Beebe and Barton’s Bathysphere

that’s just telling us about the topography of the sea bottom, the

are not our only sources of information about the deep ocean.

seamounts and trenches and Abyssal Plains that lie far below the

Everything from deep-sea fish that wash up on the seashore

surface. We know even less about the organisms that live in these

to samples trawled up in nets to satellites capable of tracking

habitats. In 2022, researchers from the Natural History Museum

ocean temperatures have informed our understanding of what’s

in London announced that about 60 per cent of DNA sequences extracted from deep-ocean sediments could not be identified

Opposite An artist’s impression of a bathysphere or deep-diving vessel. Oceanographers have envisioned a variety of ways of visiting the deep, from diving suits to submersible vehicles.

as animal, plant, bacteria, or something else. And that’s just one study, based on what little matter experts have been able to bring

16

HOW MUCH OF THE DEEP SEA IS UNEXPLORED?

17

happening down below. Even so, the very nature of the deep sea

astronaut going into space wouldn’t feel any pressure at all. But

makes it a difficult place to study.

the deeper you venture in the ocean, the greater the pressure.

Scientists sometimes comment that it’s easier to send someone

Even deep-sea animals can be limited by the increasing pressure

into space than it is for someone to visit the deep ocean. Pressure

– with ever-deeper species requiring specific adaptations to the

is a critical factor. We’re used to the air pressure on land, and an

harsh conditions – to the point that species living at the bottom

18

HOW MUCH OF THE DEEP SEA IS UNEXPLORED?

80°W

70°W

60°W

of the Mariana Trench (see pages 212–215) are under a thousand times more pressure than we experience at the surface. Designing

40°S

remote and human-operated vehicles that can withstand

45°S

the pressure and return safely to the surface is an incredibly challenging, delicate and expensive task. But we must find out more about the deep ocean. Especially as humans have an ever-greater impact on the planet, we need to know what lifeforms are in the depths to better conserve

45°S

50°S

and protect them. Even if shipping noise or human-caused climate change don’t directly touch the deep seas, the depths are still connected to the surface through phenomena such as the daily migration of plankton and nutrient cycles, during which detritus and organic matter from the surface drifts

55°S

50°S

down to feed life far below (see pages 20–25). Sometimes it seems that every time researchers venture into the deep sea, they find something new – an impression close to the mark, given all that remains to be discovered.

chlor_a (mg m^-3)

60°S

0.059

80°W

70°W

60°W

0.38

2.43

15.58

99.79

These pages Today’s satellite images and data reveal a wealth of information about our seas and oceans, from tidal currents (opposite), to immense phytoplankton blooms (above), to temperatures (left).

55°S

50°W

19

Nutrient Cycling ----·· ···················-----·· ........................

........................ ----·

.................... ----·

the oceanic depths are not disconnected from life near the surface. The two are closely connected, not just by the flow of currents or the migration of plankton but also through the behaviour of animals such as whales. This phenomenon is called nutrient cycling, a biological pump founded on whale poop.

W

hales are permanently tied to the surface because of their

Where the whales release all that nitrogen, phosphorus and

need to breathe air, but many of the foods that cetaceans

iron matters for the health of the seas. So far as marine biologists

rely upon are found in the deep ocean. Sperm whales often feed

know, whales tend to poop closer to the surface. Their faeces are

on squid that live hundreds of metres/feet below the surface, and

often cloudy, or what one biologist has referred to as “oversteeped

many baleen whales dive deep to sift krill out of the water column.

green tea”, and they are released in a large plume through the

These deep-water creatures are rich in nitrogen and iron, which

water column. The enriched faeces disperse in the upper levels of

end up becoming part of the whales’ faeces as the invertebrates

the ocean, where sunlight reaches, and become critical resources

are digested.

for plankton.

20

NUTRIENT CYCLING

not to mention that more than half the oxygen in our atmosphere

The whale pump – as biologists sometimes call it – is the

is generated by phytoplankton through photosynthesis.

opposite of another important ocean phenomenon. Small particles of biological debris and organic matter are constantly

But the way whales and other creatures nourish the seas has

drifting downward from the surface waters towards the bottom.

changed over the past several hundred years. Large-scale whaling

This is called “marine snow,” because it looks like flurries in the

decimated cetacean populations around the world, and despite

water column. This organic material often serves as food for

conservation progress many populations have never recovered

deep-sea creatures, like the krill, and so the way whales feed

to historic levels. That means fewer whales to perpetuate the

concentrates and returns essential components back near the

nutrient-cycle work, and fewer deep-sea compounds making it

surface to maintain the ecosystem.

back up to the surface. Some studies, like one carried out based

What the whales and other deep-diving marine mammals leave near the surface helps to grow a garden. Phytoplankton – tiny

Opposite Humpback whales at the surface.

organisms in the ocean that can photosynthesize, like algae –

Below Whales are an important part of nutrient cycling in the oceans, feeding deep and then leaving nutrient-rich waste products near the surface.

benefit from the nitrogen and iron released by the whales. This plankton is the foundation for much of the oceans’ ecosystems,

Zooplankton, Fish

Marine Mammals

Phytoplankton

Phytoplankton

Phytoplankton

NH4+

Krill Zooplankton (e.g. copepods)

Fish

Faeces, urea

Nutrients Faeces, migration, death

Zooplankton (e.g. copepods)

Base of the Sunlight Zone Biological pump

Whale pump

Bottom fish Benthic detritus Microbes

21

Above Humpback whales can dive over 200 metres (656 feet) below the surface in search of food. Opposite Centuries of intense whaling have dramatically affected the nutrient cycling in the oceans. Following pages Plankton are the most important organisms of the ocean. Everything from armoured amoebas to tiny fish hatchlings form the basis of ocean food webs.

22

NUTRIENT CYCLING

on the whale pump in the Gulf of Maine, off North America,

sifting krill in the ocean dark is important to our terrestrial

estimate that whales and other marine mammals such as seals

realm. Whales help feed life in the surface waters, and in turn

used to contribute three times more nitrogen to the surface before

some creatures such as ospreys and other fish-eating birds

commercial culling. Another study found that nutrient cycling in

take ocean fish and bring them inland – scattering those ocean

the Southern Ocean, off Antarctica, is only at about 2 per cent of

nutrients on land. Those nutrients then become part of the

its former abundance.

terrestrial nutrient cycle that helps plants to grow, which feeds

Marine biologists have only recently come to understand the

herbivores, and so on, with organic matter from the land being

importance of large whales to the oceans’ productivity and health.

washed back out to sea in a never-ending cycle. In the past,

For decades, whales were thought to be large creatures that

researchers estimate, this interconnected system cycled over

primarily consumed food in the ocean; we now understand them

150 million kilograms of phosphorus every year between the

to be ecosystem engineers. That history has been going on for

sea and land – an amount far greater than detected today. But

at least 40 million years, when whales began living permanently

there is good news. Through conservation and allowing sea life

in the seas, which raises questions of how other creatures – like

populations to climb, the oceans could return to a state closer

the marine reptiles of the Mesozoic era – might have affected the

to what they were like before whaling, harmful insecticides like

nutrients in ancient seas.

DDT, and other ecological hazards. The oceans’ past tells us what kind of future we can cultivate.

Naturally, life on land is connected to the seas. A baleen whale

23

24

NUTRIENT CYCLING

25

Bioluminescence ........................ ................ ................ ....................... ................ .................. ..................... ................ .................. ...... .............. ................ .................. ..................... ................ ....................... ................ ................ ...

If you stand on the beach at night, you might get treated to one of nature’s more spectacular light shows. Waves sometimes spread towards the shore with vibrant hues of neon blue lighting up the dark surface. This isn’t an optical illusion: it’s a common form of bioluminescence, a widespread natural phenomenon that takes place from our back gardens to the deep sea.

R

educed to its simplest expression, bioluminescence is light

creatures like lanternfish have photophores along the sides of

produced by a living thing. Many different organisms can

their bodies to help disrupt the silhouette of their body.

bioluminesce, ranging from bacteria to fungi to fireflies. In short,

Bioluminescent animals can pull some other flashy deep-sea

light-emitting molecules called luciferins interact with enzymes

tricks. Not only do the arms of the squid Octopoteuthis deletron

called luciferases. But that’s hardly all. These compounds are

emit light, but the cephalopod can jettison parts of an arm at will

usually in bacteria that colonize the tissues of organisms, often in

– and the glowing, twitching chunk can distract a predator while

specialized light-emitting cells called photophores. From a firefly

the squid makes its escape. A deep-sea shrimp called Acanthephyra

on a summer night to the glowing waves on the shore, it’s this

purpurea uses a different technique to achieve similar ends. In

interplay that allows life to make light.

addition to having photophores on the outside of its body, the crustacean can ooze a bright bioluminescent fluid, much like a

Sometimes bioluminescence is meant to advertise and attract,

glow-in-the-dark version of squid ink.

as in insects that flash lights to entice mates. But especially in the dark of the deep sea, where sunlight never reaches,

Of course, no glowing organism in the seas is quite so famous

bioluminescence can take on different roles – including

as anglerfish. These fish are not a singular species, but an entire

camouflage. Even though lighting up bright might seem to

order – called lophiiformes – that use specially evolved lures to

make an organism more conspicuous, creatures that live in the

help entice their prey. These striking fish have larger females that

Twilight Zone and below can emit light to startle or throw off

come to mind when we think of “anglerfish”, while the males are

their predators. Cookie-cutter sharks (see pages 98–99), for

tiny fish that only seek to attach to and parasitize the female (see

example, have a strong glow along their undersides – likely a way to make predators below them confuse the brightness of the shark’s underbelly with the tone of the lighter waters above.

Opposite above Firefly squid are masters of ocean camouflage. The bright spots help break up their outline and confuse their shape.

Firefly squid use the same camouflage technique, and other

Opposite below Firefly squid glow at the water’s edge during mating.

26

BIOLUMINESCENCE

27

28

BIOLUMINESCENCE

pages 132–135). And situated on the heads of these females, above

species. Midwater is almost like space – expansive and seemingly

a mouth full of pointed teeth, are lures that they can wiggle just

borderless. Many species that live in midwater spend their entire

so to entice prey. Among deep-sea species, those lures often glow.

lives in the ocean void. But the bottom is often murky and strewn

In the case of the anglerfish, the bioluminescence comes from

with rocks and other obstacles that makes visual communication

bacteria that contain the light-emitting compounds. The relationship

less effective, not to mention that many animals can hide by

between fish and bacteria is an example of symbiosis – when two

digging in rather than flashing.

different organisms become biologically reliant on each other in the

There are probably many more deep-sea species that can glow

same body – and the tie is so tight that some anglerfish bacteria can’t

and flash that are still to be discovered. Of the species we do

survive outside this environment. How this relationship started is

know about, those that can give off light often only do so as a

unknown, but researchers have detected that the bacteria inside the

form of defence. By spending more time in the dark water, we

anglerfish lure are still evolving and losing genes.

may eventually be able to shed light on all the incredible ways these creatures make and use bioluminescence.

Scientists have recorded an entire aquarium’s-worth of glowing deep-sea species – squid, fish, corals, jellyfish and more. But as common as bioluminescence is, the sea isn’t entirely aglow from

Opposite Anglerfish use bioluminescence to catch prey.

top to bottom. In midwater, below the Sunlight Zone, about three

Above A bioluminescent tunicate. The light is created by the interaction between compounds called luciferins and enzymes called luciferases.

quarters of known species can emit light. Along the sea bottom itself, the ratio of bioluminescent species drops to less than half.

Following pages A lanternfish with bioluminescent fins and tail to disguise its shape.

That makes sense for how the habitat shapes the lives of deep-sea

29

100 metres

T Frilled Shark In 1884, American ichthyologist Samuel Garman reported on a strange fish caught in Japan’s Sagami Bay. This creature, Garman wrote, was “An Extraordinary Shark”, an eel-like species with odd, multi-cusped teeth that looked like little pitchforks. Odder still were the shark’s gills, six seemingly “frilled” pairs instead of the five slits most sharks have.

G

arman codified these strange features in the shark’s name – Chlamydoselachus anguineus, the “eel-like shark with frills”.

Marine biologists weren’t entirely sure what to make of the

shark at first. The long, slender fish had a number of ancient traits that seemed to have more in common with fossil sharks than the likes of tiger and white sharks. Depending upon whose authority you relied, the frilled shark might be a surviving relative of early sharks such as the fossil Cladoselache, the spike-headed fossil shark Xenacanthus, or some other prehistoric group. In time, however, biologists realized that the frilled shark is a relative of today’s cow sharks – or hexanchiformes – that are often found in the deep sea. Even though frilled shark fossils have been discovered, these are from the Pleistocene era or Ice Age, and indicate that the shark isn’t quite the “living fossil” it’s often been portrayed as. Much like the distinctive goblin shark (see pages 88–91), the frilled shark can be found off the coast of most continents. Specimens have been spotted from New Zealand to the East Coast of the United States. The sharks seem to favour waters between 50 to 100 metres

Above Samuel Garman was the first ichthyologist to describe the frilled shark.

(164–328 feet) deep along the continental shelves, although they don’t stay put in the deeper parts of their range. The sharks feed

Opposite Frilled sharks often spend the daylight hours in the depths and come closer to the surface at night.

on fish, squid, smaller sharks, and other deep-water creatures that

32

FRILLED SHARK

But the shark might have a sneakier method. The multiple rows

migrate up towards the surface at night. During the day, or when

of multi-pronged teeth lining the frilled shark’s jaws are so densely

the upper water layers grow too warm, the sharks go deeper. Studying the feeding habits of this unusual shark has been a

packed that they appear lighter in colour, even in deep waters,

difficult task, but marine biologists have been able to piece a few

acting as a kind of lure to small prey that might be attracted to or

things together about the predator’s behaviour. The frilled shark

confused by the light. Once the prey gets close, the shark can open

is not a fast swimmer and doesn’t even have a particularly strong

its jaws quickly enough to create suction and slurp the prey inside.

bite, but instead focuses on squishy prey like squid, or organisms

The sharks are often seen as solitary hunters, but, like many

that might be exhausted after spawning. Despite being a fluid

other deep-sea creatures, they do come together to socialize for at

medium, water is still viscous enough that frilled sharks can

least one important event – mating. In 2008, researchers reported

spread their pectoral fins to brace against the water and throw

on more than 30 frilled sharks captured along the Mid-Atlantic

their spiky jaws forward in a rapid strike.

Ridge over an undersea mountain. Such an aggregation of frilled

33

34

FRILLED SHARK

sharks had never been seen before. And encountering such an

by palaeontologists. Some gaps in the fossil record of deep-sea

event truly was by chance. While not the deepest-dwelling sharks,

animals – like the 66 million years between fossil and living

frilled sharks still live deep enough that they’re not directly

coelacanths – is created by an imperfect geological record. In the

affected by changing seasons above. Changes in light levels and

case of frilled sharks, most fossils are from ancient, shallow-water

temperatures from the surface don’t regulate when they breed.

environments. When the sharks began inhabiting deeper waters,

The sharks reach sexual maturity when they reach about 1 metre

they were not preserved as readily. The deep sea is also less susceptible to the perturbations that

(3 feet) or more in size, although how these sharks determine

are common at or near the surface. There are no strong ocean

when to congregate is still a mystery. Why is the deep ocean home to so many primitive-looking animals

currents, dramatic seasonal changes in light and temperature, or

like the frilled shark, coelacanth (see pages 44–49) and vampire squid

direct interference by humans. Deep-sea niches may last longer

(see pages 66–69)? There’s no single explanation, but rather several

and be more stable, requiring less change for creatures suited to a

factors that affect our perceptions of evolution in the deep.

particular way of life. Today’s frilled shark is not unchanged from its ancestors, but its very characteristics and adaptations still suit

Despite the fact that most of our planet is ocean, and watery

a life in the dim and the dark.

environments often have plenty of sediment to bury animal remains, fossils from deep-water environments are very rare.

Opposite Frilled sharks can often be identified by their distinctive, multi-cusped teeth. The bottom image shows a tooth row from the lower jaw.

Sediments that turn to rock layers more commonly accumulate closer to shore, and become compressed over time. Those rock layers then shift with the continents and sometimes are

Above While most species of living sharks have five gill slits, the frilled shark has six.

brought back up to the surface, where they can be investigated

35

100 metres

T Biogenic Sediment Where did the seafloor come from? It might be easy to think that the seafloor has always existed, an undersea landscape that remains virtually undisturbed compared to our terrestrial realm.

B

ut the seafloor is constantly, imperceptibly changing. From

in the seas – not just the ocean giants or creatures visible to the

undersea volcanoes to dust carried out to sea by the wind,

naked eye, but the plankton and other microorganisms that are

the sea bottom comes together from a variety of different sources

so numerous as to be beyond counting. It’s the remnants of these

– including the organisms that live in the oceans. A great deal of

organisms that make up much of the muck on the seafloor. A portion of the world’s biogenic ooze is made up of hard

ocean sediment is what researchers call biogenic ooze. Even though a great deal of Earth’s sediments are made up of

parts from large animals, or at least ones big enough to easily

older stone that has been broken down into tiny pieces, biogenic

see. The beaks of squid, the scales of fish, the teeth of sharks, the

ooze is the remnant of life itself – a slurry of biological titbits

exoskeletons of crustaceans and more can become part of the

that are more resistant to breaking down. Think of all the life

sea bottom as they are shed or discarded and drift down into the

36

BIOGENIC SEDIMENT

abyss. But all of those larger organisms rely on a much broader

days. Depending on how close to shore plankton or other hard

and prolific array of tiny creatures to survive, many of which

parts begin to sink, the components of the biogenic ooze might

form their bodies or protect themselves with hard tissues.

travel kilometres/miles down before touching the bottom. The

Earth’s seas are absolutely brimming with armoured life

process can turn into a journey of more than a decade, acting as

forms. Foraminiferans, for example, are essentially amoebas

a record of what life was like in the upper zones of the ocean. In

that grow shells around themselves and are part of the oceans’

fact, geologists and other researchers interested in Earth systems

plankton. Coccolithophores are almost like an algal equivalent,

often sample biogenic ooze to better understand how phenomena

plants that form hard discs and are often arranged in balls

such as climate have shifted over time.

called coccolithospheres. And, as gardeners might know, the

When organisms like foraminiferans and coccolithophores make

oceans are also full of diatoms – a single algae cell that is

their shells, they incorporate isotopes of oxygen from seawater into

enclosed in a shell – that are sometimes sold as “diatomaceous

their hard parts. The nature of these oxygen isotopes is affected

earth” in garden shops. These organisms and more – such

by local seawater, which is in turn influenced by how much fresh

as tiny crustaceans called amphipods, or protozoans called

water is frozen into ice sheets and glaciers. During colder climates,

radiolarians – live and die by the billions upon billions upon

when there is a greater amount of ice at the poles, planktonic

billions, and when they perish, their hardened bodies sink towards the bottom. They are part of a constant rain from

Opposite The white chalk cliffs on England’s southeast coast were formed from calcareous oozes during the Cretaceous period.

above called marine snow, and, like snow, they accumulate in soft drifts as the seafloor is constantly remade.

Above Foraminiferans are so numerous that their hard “tests” can form sediments in the deep sea.

This accumulation doesn’t happen in the span of hours or

37

shell-builders incorporate O18 into their hard parts. When the climate warms and glacial meltwater changes the ocean chemistry, however, seawater has more O16, and so the ratio shifts. Based on this relationship, experts can look at samples from biogenic oozes – either fresh or ancient – and track how the global climate has shifted between warm and cool conditions through time. Each of the hard-bodied organisms in the seas uses different minerals and molecules to create their tough outer coverings. Diatom tests are often made of silica (SiO2), while foraminiferans and coccolith shells are made of calcium carbonate (CaCO3). Biogenic ooze that’s primarily made of foraminiferans or coccoliths is often called calcareous ooze; it can be compressed and transformed into chalk over time. The world-famous White

Top The ocean is full of invertebrates with hard shells, such as amphipods.

Cliffs of Dover, for example, are calcareous oozes that formed at the bottom of the sea during the Cretaceous period – a term

Above Coccolithospheres are made up of many individual coccoliths, or disc-shaped algae.

that itself means “chalk”. Even though the surface of the sea might seem uniform or plain, these cliffs are a cross section that testifies

Opposite Many deep-sea sediments are principally made of diatoms that have drifted to the bottom.

to the ongoing accumulation that underlies our oceans.

38

BIOGENIC SEDIMENT

39

120 metres

T Megamouth Shark On 15 November 1976, the US naval vessel AFB-14 was off the Hawaiian island of O’ahu when something became tangled in the ship’s anchor line. Something big. When the line was raised to the surface, a shark 4.5 metres (14 feet 9 inches) long was caught in it – a shark that couldn’t immediately be classified. It had a passing resemblance to some other sizeable ocean sharks, but instead of large, serrated teeth, the new shark had rows of tiny, triangular teeth that better fit the lifestyle of a filter-feeder. Formally described for the first time in 1983, this was

Megachasma pelagios – the megamouth shark.

"

,,

40

MEGAMOUTH SHARK

R

esearchers are still puzzled by this shark. It’s one of several

feet). But at night, as plankton rose closer to the surface, the shark

large, filter-feeding sharks alive today – like whale and

followed and stayed between 12 and 25 metres (39–82 feet) down, before returning to the depths in the morning.

basking sharks – but evolved its method of sieving small prey from the water entirely independently. Even stranger, the megamouth

While streamlined, the megamouth shark doesn’t look quite so

belongs to the same group of sharks as the famous great white

sleek and lithe as other shark species. Many sharks have stabilizing

and mako sharks, the lamniformes, and has fossil relatives dating

features near the base of the tail called caudal keels, for example,

back at least 34 million years. As far as marine biologists presently

and the megamouth lacks these. But that makes sense for a slow-

know, adult megamouth sharks can get to be about 5.5 metres (18

moving filter-feeder. Despite following plankton up through the

feet) long and live between the surface and depths of 1,000 metres

water column at night, megamouths don’t chase food – all they

(3,280 feet) in tropical and semi-tropical waters around the world.

have to do is open their mouths, and the specialized rakers on

Part of what makes this shark so difficult to understand is

their gills strain plankton and other small prey from the water.

that much of what researchers have been able to observe comes

They live at such depths, and are so big, that adult megamouths

from dead specimens rather than glimpses of the living animal.

are not usuallly in danger from predators – much like the giant

Examinations of dead megamouths have revealed that the inside

oarfish (see pages 100–103). While other sharks have adapted to

of the shark’s upper lip seems to be a bright whitish colour. At first,

be warm-bodied, supercharged carnivores, the megamouth lives

experts thought that this strip glowed in the deep – a bioluminescent

a slow-and-steady lifestyle reliant on abundant prey.

lure for plankton to come closer. But later studies found that the

The sharks live such a relaxed lifestyle, in fact, that there isn’t

strip doesn’t produce light and instead is very good at reflecting it.

much genetic difference between megamouth sharks found in

It’s possible that these reflectors help megamouths find each other

different oceans. This is often a major query for biologists – how

in the deep, or maybe they play some role in feeding, or perhaps

many species or distinct populations of a species are there? However,

something else entirely, but it’s difficult to tell when unobtrusively

in the case of the deep sea, the conditions far down are often so stable

observing the sharks is so challenging. So far, only about 100

– and relatively similar around the world – that large animals can

megamouth sharks have either been seen or caught.

venture far and wide and be part of a global population rather than

Nevertheless, a few chance encounters have given biologists

differentiated pockets. But there are some blank spots in the fossil

clues about how megamouths spend their time. While Megachasma

record of megamouth sharks, so the next “new” Megachasma species

can certainly be called a deep-sea shark, the filter-feeder doesn’t

is more likely to be found in the rock than in the seas.

spend all of its time below the Sunlight Zone. In 1990, researchers radio-tagged and released a megamouth shark and analyzed the data sent back. The shark never moved particularly fast, cruising

Opposite The first megamouth shark was discovered when the fish became accidentally entangled in a US Navy ship’s anchor.

along at 1 or 2 kilometres (about 1 mile) per hour, and it spent

Above The megamouth shark is a filter-feeder.

most of the daylight hours between 120 and 160 metres (393–525

Following pages Living megamouths have rarely been photographed.

41

150 metres

T Coelacanths There was a strange, rarely seen fish that lived off the coast of South Africa. People there knew the odd creature as “gombessa” or “mame”, a fish that seemed to live deep down and only occasionally made an appearance in fishing nets. But it wouldn’t be until 1938 that Western scientists would know of the gombessa, an animal they thought long extinct.

W

hat unfolded on 23 December 1938 would soon turn the gombessa into a star. That morning, trawler captain Hendrik

Goosen called the curator of the small museum in East London, South Africa – Marjorie Courtenay-Latimer. His nets had brought up a particularly strange fish and he had set it aside for CourtenayLatimer in case she might want it for the museum. The crew took great care with the fish, trying to preserve it as best they could for their arrival at the harbour, despite the fact that the original dark blue of the fish’s scales was fading to grey on their approach. Courtenary-Latimer immediately knew that the fish was unlike anything in the museum, though she wasn’t entirely sure what it was. With the local fish expert out of the office for the end-ofyear holidays, she had a taxidermist preserve the fish as best they could. When James Leonard Brierley Smith eventually saw the

sarcopterygians have many large, hand-like bones inside fleshy

taxidermized mystery, he recognized it as a fish that was thought

fins. This anatomical setup actually makes coelacanths more

to have been extinct since the time of Tyrannosaurus Rex. For

closely related to land-dwelling vertebrates – including our

scientists, the fish was proof that coelacanths still lived.

amphibious ancestors – than other fish.

Coelacanths have a very long history. These bony fish first

Despite being prolific and sometimes reaching fantastic sizes

evolved about 410 million years ago, part of a diverse family

– such as the Cretaceous coelacanths that grew to be as large

called sarcopterygians. While they had interior skeletons made of

as today’s great white sharks – the fossil record of coelacanths

bone, like many other fish of that time, their fins were markedly

almost entirely vanishes at the 66-million-year-old mark. (There

different. Instead of the fleshy fins of a shark, or fins made of a

have been some supposed coelacanth fossils dating to the past 66

membrane stretched over fin rays, like most fish alive today,

million years, but these are rare and still questioned by experts

44

COELACANTHS

Opposite Marjorie Courtenay-Latimer’s quick thinking and persistence were essential to the scientific discovery of the coelacanth. Top Coelacanths have an extensive fossil record, stretching back over 410 million years. Above Preserved coelacanth (Latimeria chalumnae) found off the Comoro Islands, Indian Ocean. The specimen has been bleached out by the preserving effects of formaldehyde.

45

46

COELACANTHS

given the difficulty in uncovering deep-sea fossils.) The discovery of a living coelacanth was like discovering a living descendent of Triceratops, a still-surviving remnant from the deep past. Smith named the coelacanth caught off South Africa Latimeria chalumnae, a fish that could grow to 2 metres (6 feet 6 inches) in length, and eventually wrote a book about it called Old Fourlegs. But what no one knew was that the events of 1938 would be repeated. There was another living coelacanth species that would be discovered decades later. On 18 September 1997, an American ichthyologist and his wife were browsing the stalls at a fish market in Indonesia while on honeymoon when they spotted a weird – but familiar – fish. It looked like the gombessa, just with a brown body colour. When the couple posted photos from their trip online, ichthyologists immediately began to speculate that this was a second coelacanth species. Additional specimens eventually confirmed that guess – there is a second living coelacanth species, Latimeria menadoensis. In fact, despite looking so similar to each other, the last time the two coelacanth species shared a common ancestor was over 30 million years ago. Genetic analyses have also indicated that coelacanths evolve slowly, despite how long ago they split into different species, and this may account for why fish that have been evolving independently of each other for so long retain so many similarities. Modern coelacanths seem to live around the border of the Sunlight Zone and the Twilight Zone, around 90–150 metres (295–492 feet) below the surface during the day. They often rise at night, hunting for cephalopods and fish in waters about 55 metres (180 feet) deep, before returning to deeper water. Based upon where they live and how they spend their days, it seems that coelacanths prefer dim or dark waters which are neither warm nor cold – around 18–20°C (64–68°F). The temperature range seems to be important for the fish’s physiology, yet coelacanths have a little trick to keep them from being too ecologically inflexible. If food seems scarce or the right conditions are hard to find, coelacanths can significantly slow their metabolisms to get by on less food and sink to lower depths to go into a sort of hibernation until conditions improve. If deep water has been a refuge for coelacanths since the last days of the dinosaurs, such a strategy might have allowed them to persist through the ages. Left In life, coelacanths are a striking royal blue in colour. Following pages Coelacanths belong to a group called sarcopterygians, or “lobe-finned” fish that have fins which are more anatomically similar to our limbs than to the ray fins of other fish.

47

48

COELACANTHS

49

550 metres

•

~

Azoic Hypothesis On the surface, a paper titled “Report on the Mollusca and Radiata of the Aegean Sea” might not seem to be an especially thrilling document. Presented by naturalist Edward Forbes to the British Association for the advancement of science in 1843, the document covered the various bivalves, cephalopods, starfish and other invertebrates found in the pocket of ocean between southern Europe and Asia.

S

uch taxonomic lists were common in the age of colonialism,

with now. The uppermost parts of the Aegean were full of brown

when various parts of the world were being mapped and

kelp, fish, oceanic invertebrates and other forms of life. Forbes’

documented. But Forbes didn’t shy away from the theoretical.

next layer was the corraline zone, where plants became scarce

His report also contained a hypothesis that would frame people’s

due to diminished sunlight and corals were more common.

ideas about the seas for over two decades. The deep sea, Forbes

Below that, Forbes thought, were deep-sea corals that acted as a

suggested, was almost devoid of life.

last holdout for the few species that could survive the darkness

Forbes based his idea on his experiences aboard HMS Beacon in

and pressure. And below that? Seemingly nothing. Even though

1832. Acting as the ship’s naturalist, Forbes set about dredging the

Forbes was not the first to suggest the idea, he had found what

sea at various depths and locations within the Aegean Sea as the

he thought was the direct evidence of how sea life faded out with

Beacon made its survey. His goal was to better understand where

each successive metre.

ocean species were found, both geographically and at depth – or

Forbes was not able to sample the deepest zones of the sea, his

what biologists call the distribution of species. Forbes noticed

being a time long before submersibles or any appreciation of how

something curious. The deeper he dredged, the variety of species

truly deep the world’s oceans are, but, based upon his samples and a

coming up seemed to shrink – not to mention the size of the

little mathematical wrangling, Forbes proposed that depths below

creatures themselves. The deeper the water, it seemed, the more

550 metres (1,804 feet) would contain no life at all. The idea became

sparse life became.

known as the azoic hypothesis, azoic meaning “without animals”.

In Forbes’s view, the depths of the ocean seemed to be

The azoic hypothesis – sometimes called the abyssus theory

organized into a different set of zones to those we’re familiar

– could have been a blip on the scientific radar. At the time,

50

AZOIC HYPOTHESIS

our understanding of the deep sea was incredibly minimal, not

found life even deeper down, dredging up evidence of organisms

least because researchers could only get a surface view (many

from below 4,000 metres (13,123 feet). If that wasn’t enough, the

nineteenth-century books present illustrations of sea life stranded

voyage of HMS Challenger between 1872 and 1876 would come

on the beach, because knowledge of what the animals looked like

back with evidence of life from some of the deepest parts of the

underwater, in their natural habitat, was extremely limited). But

ocean, more than 8,000 metres (26,246 feet) down.

other experts helped to bolster Forbes’s notion. Naturalists were

Naturally, Forbes was working with what he had. The Aegean is

beginning to understand that pressure in the ocean increased

not the most biodiverse area of the world’s seas, and the dredges

with greater depth. In 1867, for example, geologist David Page

that he used were relatively simple. Then again, decades before

noted that water became ever more compressed the deeper the

his pivotal paper, naturalists had been finding invertebrates such

ocean got. “At this rate of compression,” Page wrote, “we know

as worms and starfish from lower depths than those that Forbes

that at great depths animal and vegetable life as known to us

suggested were lifeless. He probably just didn’t know about it

cannot possibly exist – the extreme depressions of the seas being

because not all scientific results at the time would become widely

thus … barren and lifeless solitudes.”

known. But, as historians of science have noted, there was a

Page’s confidence was misplaced. Some creatures that were

benefit to Forbes’s conjecture. It got people to go out and look,

already familiar to naturalists of the time, like the giant squid,

to double-check and explore, and those explorations eventually

lived at greater depths than Forbes proposed. Experts just didn’t

revealed an abundance of life that would have likely thrilled such

know how deep because it would be over a century and a half

a pivotal figure in the history of oceanography.

before anyone would see a healthy giant squid in its natural habitat. But even ship- and shore-based surveys were starting to turn up evidence that the seas didn’t follow Forbes’s expectations. Around the time of Page’s considerations of pressure, Norwegian

Above left Edward Forbes proposed the azoic hypothesis in 1843, based on observations of creatures in the Aegean Sea.

biologist Michael Sars reported more than 400 different species found at depths below 800 metres (2,624 feet) – far below

Above right Charles Wyville Thomson was among the experts who would eventually disprove the azoic hypothesis.

Forbes’s cutoff. Scottish naturalist Charles Wyville Thomson

51

several hundred metres

•

~

Cambrian Creatures For most of Earth’s history, the oceans might have seemed empty. Bacterial life and organisms like cyanobacteria – which helped oxygenate Earth’s atmosphere – abounded, but there were no multicellular organisms or animals. Life evolved by about 3.22 billion years ago, but there was nothing more than single-celled organisms for over a billion years after that – palaeontologists even call the time period between 1.8 billion years ago and 800 million years ago “The Boring Billion”, as life seemed to go through a long, grinding lull.

B

ut by 541 million years ago, something astounding began to

Kangaroo Island, off the south coast of Australia, is another

happen. Not only had early animals evolved, but they also

hotspot for Cambrian fossils. The Emu Bay Shale contains fossils

began to flourish into an incredible variety of forms. This was the

of many soft-bodied animals preserved in fine sediment. The

“Cambrian Explosion”, and it included creatures of the deep sea.

creatures here come from deeper waters, estimated to be several

The most famous fossil site documenting the Cambrian

hundred metres/feet below the surface, and the rocks formed

Explosion is British Columbia’s Burgess Shale. It’s taken decades

at greater depth than the Burgess Shale. These fossils are also

for palaeontologists to comprehend what they’re looking at

geologically younger, about 515 million years old, and include

when they study these fossils, with some creatures mistakenly

different species than those found elsewhere.

restored upside down as part of the learning curve. There were

Among the finds of the Emu Bay Shale are eyes from creatures

spiky worms, animals that looked like pincushions, predators

called anomalocaridids. They were often the predators of their

with compound eyes and grasping appendages set in front of a

time and were related to early arthropods. Encased in tough

shutter-like mouth, all while our own predecessors were pencil-

exoskeletons, these animals could grow to more than 1 metre

long, worm-like swimmers that didn’t even have a backbone yet.

(3 feet) long, had mouths like camera shutters, grasping arms in

But the Burgess Shale represents a shallow-water reef out on the continental shelf. Palaeontologists have had to look elsewhere to

Opposite The famous Burgess Shale is exposed in the mountains of British Columbia.

find out what was going on in the deep sea.

52

CAMBRIAN CREATURES

53

54

CAMBRIAN CREATURES

the lower Sunlight and upper Twilight Zones of today’s seas.

front of those mouths, and moved about by flapping wing-like fins along their sides. In fact, palaeontologists have speculated that

Fearsome as “Anomalocaris” briggsi might have looked, though,

such creatures might have helped set off the Cambrian Explosion.

experts think that this animal fed on some of the ancient oceans’

Anomalocaridids had compound eyes that were much better at

smallest inhabitants. Unlike some other anomalocaridids, the

seeing prey, which required that other species evolve new defences.

eyes of this particular species were not on stalks but set into

It’s a wonder that the Emu Bay Shale fossils were preserved at

the exoskeleton of the head. The arms of the animal were better

all. The Cambrian was a world of invertebrates and soft-bodied

suited to filtering plankton out of the water column than grasping

creatures. Bone, the tissue that makes up most of our skeletons,

worms or other small prey, as other Anomalocaris species did.

had not evolved and so the hardest materials were structures like

Palaeontologists think that “Anomalocaris” briggsi looked upwards

the keratin covering the bodies of ancient Australia’s invertebrates.

to detect plankton glinting in what little light penetrated the deep

The corpses of these animals had to be buried rapidly, and even

ocean waters, and sieved its meals from such planktonic clouds.

then experts might only find a partial fossil. At Emu Bay, though,

Animals like “Anomalocaris” briggsi were new on Earth. There

palaeontologists have found anomalocaridid eyes that are so well

had never been large filter-feeders before. But the animal helped

preserved that individual lenses of the predators’ compound eyes

to pioneer a niche that other organisms would evolve to fill time

can be seen. Experts have found more than 30 of these eyes so far,

and time again, beginning interactions that can still be found

some of which are 4 centimetres (1½ inches) in diameter: together,

in our modern seas, not unlike today’s vampire squid or other

these specimens help to outline the lives of these unusual arthropods.

invertebrates that pluck their meals from the water column.

Fossil eyes from one species in the Emu Bay Shale, temporarily

Opposite Exceptional Cambrian fossils have been found in the Burgess Shale.

called “Anomalocaris” briggsi until it is officially described, are very large compared to those of its relatives. The eyes also seem to have an

Above Anomalocaris and its relatives were among the largest animals of the Cambrian.

“acute zone” of larger lenses in the centre, where the eye’s resolution is enhanced. Together, these facets of the animal’s anatomy hint that

Following pages Life in the Cambrian ranged from sponges and worms to creatures with strange anatomies, such as Anomalocaris.

“Anomalocaris” briggsi could see in relatively dim waters like those of

55

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CAMBRIAN CREATURES

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600 metres

•

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Giant Spider Crab No major aquarium seems complete without giant spider crabs. Known to researchers as Macrocheira kaempferi, these orange-and-yellow crabs look otherworldly. Their bodies are not particularly large, about the size of a watermelon, but their four legs and two arms have an incredibly impressive span – up to 3.7 metres (12 feet 2 inches) from claw to claw. The crabs are also quite heavy, up to 19 kilograms (41 pounds). As everyday as they might seem, they are truly exceptional invertebrates.

K

nown to the Japanese as taka-ashi-gani, giant spider crabs did not get their scientific name until 1836. In that year,

Dutch zoologist Coenraad Jacob Temminck described the huge invertebrate – the species name “kaempferi” referring to German doctor Engelbert Kaempfer, purportedly the first European to see this creature. The crabs principally live around the Japanese archipelago at depths between 20 and 600 metres (65–1,968 feet), wandering around the soft sea bottom in search of food. These crabs are huge – the largest crustaceans known – but they’re still on the shrimpy side compared to science-fiction and horror-movie visions of enormous crabs. There’s a good reason for that. Crustaceans wear their skeletons, made of a tough but relatively flexible material called chitin, on the outside. All of

crab’s large size comes from a relatively compact body with very

the crabs’ internal organs – the nervous system, vital organs,

long arms makes sense given the mechanical constraints of how

musculature – is enclosed in this armour. That means that as

these invertebrates build their bodies.

crabs get larger and larger, they have more internal volume to

Naturally, living large comes with a mix of advantages and

decreasing surface area. There’s a limit to how large they can be

disadvantages. While larval Macrocheira start off life very small,

without becoming so heavy as to exceed the stress limits of their

the adult crabs are large enough that many potential predators

own exoskeletons. While it’s possible that there could be as-yet-

are too small to eat them. A bumpy and spiky carapace helps offer

undiscovered crabs that are larger, the fact that the giant spider

another layer of deterrence. Yet that’s hardly all. Giant spider

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GIANT SPIDER CRAB

crabs, like some other crab species, decorate themselves with

animals, giant spider crabs start off life very small – really part of

other organisms to help them blend in with the seafloor. There’s

the oceans’ plankton. Rather than producing relatively few, well-

no real strategy in what the crab selects. Almost anything will do

developed offspring, giant spider crabs go for quantity; gravid

– sponges or anemones or tube-dwelling worms, it’s all the same

female crabs can lay over a million eggs during a mating season.

to the crab. After plucking up the animal from the sea bottom,

From there, the crabs start to go through some quick changes.

the crab fiddles with it to orient how the other organism will best

In less than two weeks, whatever eggs haven’t been eaten by filter

stick and places the animal on top of its shell, where it becomes

-feeders begin to hatch. About 15 minutes later, the crabs start to

adhered. Some of these animals even begin to colonize and live on

go through a series of growth phases, each stretching out longer

top of the crabs over time, a form of living camouflage that helps

than the previous ones. These tiny, developing crabs drift along

the crabs avoid detection as octopus swim by.

near the surface for weeks before obtaining their familiar, mature

The crabs have become a rarer sight than they used to be in

shape, though it can take a decade before the crabs get anywhere

Japan’s waters. That’s because of humans. Giant spider crabs are

close to their record sizes. Giant spider crabs are thought to live as

sometimes eaten, and historic catches declined precipitously in

long as 100 years, perhaps explaining why overfished populations

the late twentieth century. Even the crabs that are hauled up today

tend to be so small.

tend to be much smaller than in the past, with legs about 1 metre (3 feet) wide instead of nearly 4 metres (13 feet). The crabs were

Opposite Coenraad Jacob Temminck formally described the giant spider crab in 1836 in honour of colleague Engelbert Kaempfer.

being taken at a faster rate than they could reproduce, and still require a great deal of help to recover.

Above Giant spider crabs can take decades to grow to their maximum size.

The way the life cycle of the giant spider crab plays out is part of

Following pages The largest spider crabs can grow to almost 4 metres (13 feet) across their spindly legs.

the challenge that conservationists face. Like many other deep-sea

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600 metres

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Ophthalmosaurus Tens of millions of years before dolphins and seals would dive deep to snack on the fish and squid that live in the ocean darkness, there was a reptile that may have done the same. Named Ophthalmosaurus

icenicus, this Jurassic creature was an ichthyosaur – or “fish lizard” – that flicked through the seas at the same time dinosaurs dominated the land. And based on the enormous eyes of this reptile, some palaeontologists suspect that Ophthalmosaurus dived very deep.

I

chthyosaurs were not dinosaurs; they were descended

small while others grew to sizes comparable to modern sperm

from a different branch of the reptile family tree. The very

whales. Even as various forms of marine reptiles evolved and

first ichthyosaurs evolved from land-dwelling ancestors over

flourished, the ichthyosaurs were the greatest success story of

236 million years ago. They were relatively small, less than

the Mesozoic seas.

2 metres (6 feet 6 inches) in length, and looked like sinuous

Ophthalmosaurus lived about 160 million years ago, in the

lizards with pointed snouts. But within 3 million years, those

later part of the Jurassic period, in seas that covered what is

small swimmers had begun to evolve into a diverse array of

now Western Europe. These ichthyosaurs were much more

ocean-dwelling reptiles. Some ate small prey while some

streamlined than their early ancestors, and about the size of

hunted reptiles, including other ichthyosaurs. Some remained

a modern dolphin. In fact, ichthyosaurs like Ophthalmosaurus

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OPHTHALMOSAURUS

have often been used as an example of convergent evolution –

One of the most striking features of many ichthyosaur fossils

to describe species that independently evolved the same shape,

is that they are preserved with the delicate bones inside the eye,

behaviour, or other similarity despite being distantly related.

called scleral rings. These bones can be informative clues about

Both dolphins and some ichthyosaurs share similar body shapes,

a creature’s habits. How well an eye is able to see is dependent

as both groups were air-breathing vertebrates that pursued

on various conditions – such as how large it is in absolute terms,

small, quick prey in the water. Ichthyosaurs even had blubber to

Opposite Ophthalmosaurus was a marine reptile that evolved a shark-like body to swim efficiently through the seas.

help keep them warm, much like whales of all sizes today. Even though there are some important differences between the oceans

Above and below Exquisitely preserved fossils have provided palaeontologists with a detailed outline of what this reptile looked like, including the large eye socket.

of the Jurassic period and today, Ophthalmosaurus and dolphins nevertheless fill the same sort of niche.

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OPHTHALMOSAURUS

how big the aperture is in the middle, and so on – and so having

true deep-sea fossils are exceptionally rare. By looking beyond

bones that outline the size and proportions of a marine reptile’s

the eyes, palaeontologists have made a case that Ophthalmosaurus

eye can offer palaeontologists clues about Ophthalmosaurus’s

really did push the limits of an air-breathing reptile. By comparing the eyes of Ophthalmosaurus to our understanding

feeding habits. Ophthalmosaurus has big eyes, large in both absolute size and

of how animals see, the ichthyosaur was probably able to

relative to the animal’s skull. In an adult about 6 metres (19 feet)

distinguish moving prey at 300 metres (984 feet) or deeper. That’s

long, the eyes were about 23 centimetres (9 inches) wide – nearly

into the Twilight Zone, but deep enough that even the most

as wide as the eyes of other ichthyosaurs that were more than

brightly lit parts of the seas would start to darken. Furthermore,

twice that length. Given that vision is such an important factor in

as the light fades, the more prevalent bioluminescence becomes

finding prey and moving though the seas, the ichthyosaur’s eyes

– lights that might have guided these predators to prey. Likewise,

must have been proportionally huge for a reason. Some experts

drawing from the relationship between body mass and how long

suspect that that reason was diving deep to snatch small morsels

air-breathing animals can stay below the surface, Ophthalmosaurus,

from the depths.

weighing around a ton (2,000 pounds) was probably able to dive

The eyes of Ophthalmosaurus seem to be adapted to low-light

for about 20 minutes – long enough for even a slowly cruising

conditions. Their overall size and the opening for light to reach

Ophthalmosaurus to reach 600 metres (1,968 feet) below the

the sensitive cells of the retina are big and resemble those of

surface and come back up again. While other ichthyosaurs and

nocturnal species. Perhaps this means that Ophthalmosaurus

marine reptiles likely stayed close to the surface, Ophthalmosaurus

hunted at night, pursuing nocturnal creatures that rose to feed in

may have avoided competition by diving deep.

the upper zone of the ocean after darkness. One of the fossil beds in England where Ophthalmosaurus fossils have been found was Zone. But where a fossil is buried doesn’t necessarily reflect where

Opposite The eye contained fragile bones arranged in a ring. This might have helped prevent it from distorting under pressure when the reptile dived.

that animal primarily lived or regularly visited, especially because

Above Ophthalmosaurus had a long snout and conical teeth.

probably about 50 metres (164 feet) deep, well within the Sunlight

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•

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Vampire Squid In the entire history of zoology, there may not be a more evocative name than Vampyroteuthis infernalis, the “vampire squid from hell”. Even better, the title is an irony. Only a threat to small plankton, the vampire squid looks far more menacing than it truly is.

T

he discovery of the vampire squid came during a time when oceanography was only just beginning to come

into its own as a science. In the mid-nineteenth century, some ocean experts thought that there wasn’t much life at all below 550 metres (1,804 feet). Trawls from greater depths turned up little, and so much of the ocean deep was thought to be azoic, or without life (see pages 50–51). The findings of the Challenger expedition in the 1870s (see pages 196–201) changed that picture, documenting many new deep-sea organisms and inspiring naturalists such as German researcher Carl Chun to go searching for even more clues about what lived far below the waves. In 1898–99, Chun was aboard the SS Valdivia, leading an expedition of the same name off Africa, when an odd cephalopod was brought to the surface. Upon closer study, the cephalopod was extremely difficult to classify. It didn’t seem to resemble any known species. In overall form, Vampyroteuthis looked like an octopus – more bulbous and less streamlined than the squid of the shallows. The cephalopod had eight arms with flexible, thorn-like projections down the

Right German naturalist Carl Chun was the first to scientifically describe a vampire squid. Opposite Illustration of the vampire squid, based on Chun’s work during the 1898–99 expedition.

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VAMPIRE SQUID

_)

67

middle, yet lacked the specialized feeding tentacles that would

more than 23 million years old, hints that vampire squid have

be expected of a squid. But the vampire squid doesn’t feed with

been in deep, oxygen-depleted environments for at least that

its arms. Instead, in place of tentacles, Vampyroteuthis has two

long. The cephalopods may have become adapted to low-oxygen

retractile threads covered in small filaments which help the

environments documented in the deep past, and hung on in such

animal detect and gather small prey and detritus that falls from

harsh habitats ever since.

above. Even though this unique creature is now recognized as

Today, vampire squid live in the ocean dark more than 600 metres

being closer to octopus than to squid, it deviates so strongly

(1,968 feet) below the surface. Even more specifically, and perhaps

from octopus anatomy that it is categorized within its own

strangely, the cephalopods prefer a part of the ocean known as

family – the Vampyroteuthidae.

an oxygen minimum zone. These oxygen-depleted layers of the

As far as marine biologists know, there is only one living species

ocean usually occur between 200 and 1,000 metres (656–3,280

of vampire squid. Once experts knew what to look for, however,

feet), and most organisms can’t survive here. But vampire squid

they began to recognize vampire squid in the fossil record. While

can. Within this zone, remote operated vehicles have been able

there is some debate, made all the more difficult by how rare well-

to document how the vampire squid feed – floating along, their

preserved fossils of soft-bodied animals are, it seems that vampire

feeding filaments extended to hopefully capture whatever pieces

squid have been around for at least 120 million years. One fossil,

of carrion or detritus they might touch. When the squid makes

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VAMPIRE SQUID

contact with food, it quickly moves towards it and then starts the

How do vampire squid manage to procreate in such a distant

process all over again. The vampire squid definitely lives life in

habitat? What scientists expect mostly comes from other

the slow lane.

cephalopods, and might change as experts learn more. It’s

Of course, there are other creatures in the deep – and some of

probably rare for vampire squid to encounter each other so when

them are predators of the vampire squid. Vampyroteuthis does not

they do and choose to mate, a male passes a cylinder of sperm

move very fast, and even its swifter movements quickly drain the

called a spermatophore to the female, which she stores in a special

animal’s stamina, so the cephalopod has two self-defence tactics.

pouch until she’s ready to fertilize her eggs and brood. When the

One is to use the bright photophores along the tips of its arms

squid hatch, they are as small as the plankton that the adults often

and at the base of each fin, setting off a disorienting light show

feed on. To avoid becoming meals, the little ones go deeper to feed

that makes it harder to locate and catch the squid in the dark

and grow until they can return to the waters they came from.

world of the deep sea. The other, which marine biologists call the pineapple posture, is to draw its arms up its body to present the

Opposite In life, the vampire squid is a deep red colour with a striking blue eye.

predator with its exposed arms covered in spines. Those spines are soft and useless as actual defences, but they might help the

Above A great deal of what’s known about vampire squid comes from dissections of specimens trawled to the surface.

squid look like too much trouble to eat.

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703 metres

•

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Nautilus Most cephalopods living in today’s seas are soft. Octopus, squid, cuttlefish, and their relatives may have internal pens or support structures, but almost all lack an external shell. That’s notably different from much of the deep past. From the time the first cephalopods appeared around 522 million years ago, many fantastic cephalopod lineages evolved elaborate and highly ornamented shells. Today, though, there is only one form of cephalopod with hard external shells like their ancient relatives – nautilus.

E

ven though we often talk about the nautilus, singular, there

and nautilus persisted. Precisely why such similar-looking

are actually six different species alive today. The most

cephalopods wouldn’t both survive is a mystery. It might have

famous of all is the chambered nautilus, Nautilus pompilius, that

something to do with differences in the way they reproduced,

bobs through the waters off Japan, Australia and Micronesia.

or changes to ocean acidity that ammonites couldn’t cope with.

Even by cephalopod standards, they look strange. The shell

Either way, by about 100,000 years after impact, nautilus were the

houses a series of chambers, each a little larger than the last, that

only shell-covered cephalopods left.

act as the nautilus’s home. Instead of sucker-lined arms, nautilus

Nautilus aren’t born with such extravagant shells. They build

have up to 90 soft, flexible appendages called cirri that are housed

them over time, throughout their whole lives. A newly hatched

in protective sheaths. And while the eyes of other cephalopods

nautilus is only about 30 millimetres (1¼ inches) across, a part

are some of the most complex and visually acute among animals,

of the oceans’ plankton. That’s a difficult spot to be in, given that

the eye of the nautilus is a simple pinhole arrangement that gives

many marine species, from small fish to massive whales, feed on

them a much blurrier view of the world. Despite jetting through

plankton. But the youngsters that survive will build their shells

our modern oceans, nautilus look just a touch prehistoric.

as they get bigger and mature. Nautilus live in the front-most

The very first nautilus species goes back to the Triassic, over

chamber of their shells, bordered along the back by a septum. The

230 million years ago. The shelled invertebrates diversified and

shell keeps building itself with the life of the nautilus, and as each

proliferated alongside their distant ammonite relatives, surviving

new chamber is added, the nautilus moves forward into the larger

millions of years as prey for the many marine saurians that evolved during the Age of Reptiles. But when a massive asteroid

Opposite Nautilus can survive to depths of about 703 metres (2,306 feet). Any lower and their shells would be crushed by the pressure.

struck the planet 66 million years ago, ammonites went extinct

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NAUTILUS

71

NAUTILUS

space (the smaller chamber behind being added to the shell’s coil).

nautilus most often feed on dead fish, the molted exoskeletons

And these shells are sturdy. They maintain their shape to about

of crustaceans and other edible detritus scattered along the sea

800 metres (2,624 feet) below the surface.

bottom. Even though nautilus in the ancient past were more varied and lived in a range of habitats and oceans, these cephalopods have

While many deep-sea creatures are world travellers, nautilus

survived by being part of the oceans’ clean-up crew.

have a more restricted range. All living nautilus reside in the Indo-Pacific, often along the deep-water edges off continental

In many ways, nautilus seem more primitive than their other

slopes. They’ve been seen in water as deep as 703 metres (2,306

living relatives. That’s not surprising given that their ancestors

feet), though they are more commonly found at slightly shallower

evolved about 100 million years before the last common ancestor of

depths than that record. And as with the coelacanth, temperature

octopus and squid. Still, in lab experiments, researchers have found

is important to nautilus. Despite living in tropical waters, they stay

nautilus to have forms of both short-term and long-term memory

deep enough to avoid temperatures above about 25°C (77°F).

that allow them to learn what a particular stimulus – such as a flash

A swimming nautilus might look a little ungainly. Gas within

of light – means, and to tailor its response with experience. Instead

the shell helps nautilus alter their buoyancy, and they also move

of merely being a holdover from deep time, nautilus hold secrets to

around by jet propulsion – expelling water to move themselves

survival that we’re only just beginning to perceive.

backwards through the water. Poor eyesight aside, nautilus cannot see where they’re going when moving backwards. survival playbook. They are largely scavengers and opportunists.

Opposite Living nautilus species are among the most archaic cephalopods, having eyes and arms that are very different from those of octopus, cuttlefish and squid.

Rather than trying to snatch prey like an octopus or squid does,

Above X-ray of a nautilus shell shows the series of chambers.

Living nautilus have also taken another leaf from the deep-sea

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730 metres

Stromatolites Even though life on Earth is constantly evolving, there are some life forms on our planet that have found a comfortable niche and are sticking with it. That’s part of the wonder of evolution by natural selection – it explains transcendent change as well as organisms that seem to vary little from their ancient counterparts. Among Earth’s greatest stalwarts are stromatolites – structures that date back to the dawn of life on our planet.

M

any stromatolites are found in shallow, sun-lit waters.

that lived in waters too saline for the amoebas to reach were able

Shark Bay in Australia, for example, is famous for the

to persist, and so the surviving structures only grow in a portion

number of pillowy stromatolites visible along the shore. The

of their prehistoric range. Then again, researchers sometimes

proximity of stromatolites to the surface makes sense. These rocky

find stromatolites where they are not expecting them – like in

mounds are not technically alive, but are instead precipitated out

the deep sea.

beneath colonies of photosynthetic cyanobacteria. At the start

In 2018, geoscientists reported that stromatolites had been

of the process, the cyanobacteria are spread over the surface of

found in 731 metres (2,398 feet) of water in the Arabian Sea.

the sediment. As they photosynthesize and release oxygen, the

Experts had not been expecting to find stromatolites so deep, well

cyanobacteria secrete sticky biochemicals that essentially glue

below the layers that sunlight penetrates. Yet there they were,

the sediment together. But the cyanobacteria need to stay on top

slowly accreting in the deep.

in order to survive. As they adhere bottom sediment particles

While stromatolites close to the surface rely on photosynthesis,

together, the cyanobacteria begin to create little pedestals beneath

those deep down rely on a different biochemical pathway. The

themselves. Most recognizable stromatolites are these advanced

stromatolites found in the Arabian Sea are chemosynthetic, or

colonies, their history glued together beneath them.

formed with the help of microorganisms that do not require

Stromatolites survive in very salty water. That’s because

sunlight. By feeding off the methane seeping from the seafloor,

lots of other organisms can eat them and break them down.

these bacteria can carry out the same kind of growth and

Scientists hypothesize that the proliferation of stromatolites

accretion as cyanobacteria do near the surface. It’s a pathway that

was curtailed with the origin of amoebas and foraminiferans (essentially amoebas with shells) that were capable of glomming

Opposite Many modern stromatolites are found near the surface in extremely salty environments.

on to the colonies and digesting them. Only those stromatolites

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STROMATOLITES

75

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STROMATOLITES

allows wildly different varieties of microorganisms to create very

was like when it was a novelty on this planet. The fact that the

similar structures.

waters the stromatolites were found in were oxygen-depleted,

The discovery raises questions about the deep history of

just like the waters of early Earth are thought to have been,

stromatolites. Fossil stromatolites, some of which date back

seems to strengthen the connection. Likewise, researchers note,

billions of years, do not preserve the species of microorganisms

the internal structure of modern, photosynthesis-dependent

that created them. Those mats of cyanobacteria – or whatever they

stromatolites seem to differ from those of fossil stromatolites.

were – are long gone, just leaving the form behind. What experts

If chemosynthesis was more important to the formation of

have been able to learn from modern stromatolites informs our

stromatolites than thought, the story of how our Earth came to

understanding of the deep past. But while it’s likely that many

be might need some major revisions. Perhaps photosynthetic

ancient stromatolites did indeed live in warm surface waters,

bacteria were not as essential for oxygenating Earth’s atmosphere

there’s also the distinct possibility that some fossil stromatolites

as was previously thought, or maybe there was a greater number

were formed in other conditions – like that of the deep sea.

of pathways for stromatolites to form. Experts are only just

Chemosynthesis has only been known to researchers for less

beginning to dig into the possibilities, following the significance

than a century, and observations of the phenomenon are even

of these modern mounds back through eons upon eons.

newer, dating to the 1970s. Ever since that time, though, scientists Opposite above Ancient stromatolites were very similar to modern forms, down to the thinly layered bands.

have wondered if this process might be related to the origin of life itself. If life did not require sunlight to originate, and instead

Opposite below Cross-section through a stromatolite shows the bands.

could survive according to alternative pathways focused on

Above Stromatolites on early Earth were probably more numerous before the evolution of organisms, like molluscs, that could eat the living colonies.

breaking down compounds like methane that naturally flow out of the Earth, then it’s possible that life didn’t begin in a warm little pool on the shore, but in the darkness of the deep sea. And if that’s

Following pages Stromatolites in Hamelin Pool in Western Australia are thought to be the oldest in the world.

the case, deep-sea stromatolites might offer a peek at what life

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79

923 metres

Bathysphere The age of ocean exploration is relatively new. Even a hundred years ago, there were only a limited number of ways you could visit and observe life beneath the waves. In the decades before SCUBA changed our relationship to the oceans, the only way to get considerable bottom time was to fit into a big, clunky, waterproof suit fitted with a heavy helmet connected to the surface by an air hose. It was either that or simply hold your breath in a shallow dive to see what you could see.

B

ut naturalist William Beebe was not content with what he

York Zoological Park office with all sorts of design plans and

could take in from the shallows. Oceanographers knew that

sketches. One such proposal came from Otis Barton, a wealthy

there was life much further down, through organisms that either

amateur naturalist, who came up with a design for a submersible

floated up to the surface in their last moments or were dredged

and was willing to fund it. Beebe was initially skeptical, especially

from the bottom. There had to be a way to get down beyond the

because he hated elaborate technology, but he was eventually won

roughly 15-metre (50-foot) range divers were constrained by. So,

over by Barton’s simple, spherical design. The Bathysphere would

with deeper waters in mind, researchers set about constructing

be a sealed ball that was lowered on a cable, supplied with air

a way to venture below the sunlight Zone – using an enclosed,

from above, as its occupants were lowered into the deep.

underwater capsule called the Bathysphere.

Perhaps such an expedition might seem quaint to us today, but

Beebe had started making shallow dives with a homemade

Beebe, Barton, and their colleagues were taking a huge risk. There

diving helmet in 1925. It didn’t take long before he started wondering about how he might explore even deeper. By 1926, he was publicly speculating about visiting deeper waters in some

Opposite Otis Barton inside the Bathysphere, which was only capable of carrying two people at a time to the deep.

kind of submersible vehicle – a disclosure that flooded his New

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BATHYSPHERE

81

was no escape hatch or even a safe way for the Bathysphere’s

922 metres (3,024 feet) down off Nonsuch Island, Bermuda. No

occupants to return to the surface in case of a problem. If the

one had witnessed the ocean at such depth, and even then the

pressure became too great for the sphere’s design, then it might

naturalists could only stay for about 5 minutes. The weight of the

collapse and crush whoever was inside. The Bathysphere did not

Bathysphere and its tether to the surface had to be treated with

have a heating system either, and it was always possible that a

great respect; if the cable snapped, there would be no way to rescue

malfunction or even an unwary animal might sever the air hose.

or recover the crew inside. In fact, such a problem did occur. While

Still, the two occupants who could fit inside would still be able

the men were still deep below the surface, the rope that guided the

to talk to the surface – relaying their condition as well as their

steel cable on to its reel had severed and there was almost none

observations – by way of a special telephone line running between

left by the time they were back on board. Still, that didn’t dissuade

the sphere and the support ship above.

them and the Bathysphere made repeated dives.

All the research and preparations dictated that the iron

Beebe took his explorations and observations to the popular

Bathysphere had to be cast twice, as the first was too heavy

press rather than scientific journals, a move that inspired

for any ship to carry. Then Beebe and Barton ran several test

contempt among colleagues. Then again, the Bathysphere was

dives, with crew and without, to make refinements and begin

sealed and no specimens could be collected during the dives –

gathering information on the creatures they could view through

only observed. Nevertheless, the Bathysphere and its explorations

the Bathysphere’s portholes. A dive on 22 September 1932 was

were famous enough to inspire the next generation of marine

broadcast live by NBC Radio Network. Then, on 15 August 1934,

scientists – researchers who can stay down deeper, longer, and

Beebe and Barton made a record-breaking and historic dive over

gather more information than Beebe could have ever dreamed.

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BATHYSPHERE

Opposite Incapable of moving on its own, the Bathysphere required a support ship to lower, raise and otherwise assist it. Above Despite the cramped conditions, the Bathysphere allowed naturalists to get some of the first direct observations of life below the Photic Zone.

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1,000 metres

Diel Vertical Migration Over decades of exploration, oceanographers have identified particular zones of the sea and refined depths where seagoing creatures live. On paper, everything can seem orderly. But the fact of the matter is that Earth’s oceans are expansive, deep, and not sharply defined. Many organisms don’t remain at a specific depth, finely attuned to its particulars, but instead travel up and down the water column. In fact, such movement is an important part of ocean biology.

E

very day and every night, plankton and the creatures that feed on these tiny organisms rise and fall following the

dark. Marine scientists know this as diel vertical migration, a regular pattern of the seas. Naturalists weren’t aware that such a pattern existed until the early nineteenth century. In 1817, the famed French anatomist Georges Cuvier noticed that tiny crustaceans called Daphnia could be found at the surface at some times and not others. The pattern wasn’t because the Daphnia were sick or dying – like some giant squid or oarfish that come closer to the surface at the end of their lives – but was a real part of their daily cycle. Experts didn’t know just how many organisms made this daily migration. It wasn’t just Daphnia. During the Second World War, for example, US Navy experiments with sonar kept detecting strange reverberations in the deep sea. While military minds fretted that these signals were being created by enemy submarines, researchers from the Scripps Institution of Oceanography discovered that the sonar was picking up dense pockets of plankton that lived at depth. And once marine scientists became aware of this layer, they found that it moved. Many, many species

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DIEL VERTICAL MIGRATION

of plankton migrated up and down the water column according

plankton and their predators stay in the deep and dark during

to light levels – as did some creatures that fed on the plankton.

the day, but rise towards the surface during dusk before sinking

Naturally, the oceans are full of organisms belonging to so

again with the dawn. This affects large creatures as well as small

many different kingdoms, phyla, classes, and more that there is

ones – the megamouth shark (see pages 40–43) feeds on plankton

no single great migration. There are several forms of migration

Opposite The daily migration of marine organisms was accidentally discovered by the US military using sonar.

made up of varied species. The most common and most well-known form of the

Below Daphia provided the first evidence that some sea creatures migrate daily through the water column.

phenomenon is the daily nocturnal vertical migration. Deep-sea

85

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DIEL VERTICAL MIGRATION

and so follows their migration pattern. Other organisms rise during the day rather than at night, some might rise and sink according to the seasons, and some rise in the evening, sink, rise again in the morning, and sink again to make two trips in a day. Some organisms – such as giant spider crab larvae (see pages 58–61) or hatchlings of giant oarfish (see pages 100–103) – spend the earliest parts of their lives closer to the surface before going lower as they increase in size. For one reason or another, the oceans’ plankton are almost always in motion through the layers of the seas. But how do these organisms know when to rise through the water column and when to sink? It may not be a sense of knowing so much as responding to particular cues. Some cues come from the environment and are part of the oceans’ daily rhythms, like changes in light or shifts in temperature. Organisms may simply follow the conditions where they feel most comfortable. But there are likely some internal triggers for these daily migrations, too. Experiments with tiny crustaceans called copepods have found that these tiny animals continue to migrate up and down through the water column each day when they are kept in total darkness in the lab, and a few other organisms have been shown to do the same – moving regardless of the light. It might, in part, be their biological clock that makes them rise and sink no matter the surrounding conditions. In other cases, small animals may seek refuge at different depths – where predation is lessened – and will change where they live as they become larger. The various forms of migration are critical to ocean health. Life in the deep ocean is largely fed by detritus and decaying organic matter that falls from the upper zones. If all those nutrients just stayed at the depths, then life in the higher zones might be sparser. But in addition to animals – like some whales – that feed at great depth and excrete some of the nutrients back near the surface (see pages 20–25), deep-dwelling plankton that migrate upwards also become food for organisms that dwell in those upper layers. This interaction helps return some of the nutrients that fall to the deep sea back to creatures in the Sunlight Zone. Even though the nature of these migrations is still mysterious, we know that they are essential to the wellbeing of the ocean.

Left Copepods and other plankton form the foundation of ocean ecosystems, so many animals that feed on plankton follow them up and down between night and day.

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1,000 metres

Goblin Shark Not all strange fish are first seen in the depths. The world’s fossil record retains patchy evidence of the deep through the ages, and sometimes scientists find the fossils of strange creatures before they realize such species are still with us. The sleek, strange goblin shark that swishes through the modern-day deep is one such case.

I

n 1887, British naturalist and fossil fish expert James William

still true that goblin sharks – like today’s Mitsukurina – have

Davis described a strange fossil shark found in Sahel Alma,

been around for a very long time, since before the days of Tyrannosaurus and Triceratops.

Lebanon. It was a stunning specimen, complete from nose to tail and with an outline of the shark’s body – much more informative

Like many other large, carnivorous members of the deep-

than the handfuls of fossil teeth that many ancient sharks are solely

sea community, goblin sharks live in deep water off the world’s

represented by. Davis named the shark Scapanorhynchus lewisii, a

continental shelves. Goblin sharks have been observed or caught

fish that had lived millions of years ago and was presumed extinct.

off the coasts of North and South America, Africa, Europe, Asia

Just over a decade later, in 1898, the American ichthyologist

and Australia, often at depths between 200 and 1,000 metres

David Starr Jordan studied an odd shark that had been caught

(656–3,280 feet), although some go deeper. A goblin shark tooth

in Japan’s Sagami Bay. The fish didn’t look quite like anything

was once found embedded in an undersea cable at about 1,370

anyone had seen before. The shark had a long, tapering body and

metres (4,494 feet) down.

a flat, shovel-like snout that left its needle-toothed jaws hanging

Why a goblin shark might try to bite a chunk out of an

below. Jordan named the shark Mitsukurina owstoni; the common

undersea cable might have something to do with how sensitive

name is a translation of its Japanese name, tenguzame, reflecting the shark’s likeness to Japan’s mythological, long-nosed tengu. Opposite above While many photos of goblin sharks show them with their jaws extended, most of the time the shark’s jaws fit neatly beneath its long snout.

Other naturalists soon recognized the resemblance between the fossil shark and the goblin shark caught in Sagami Bay. In fact, some experts even thought that they might be the same

Opposite below left Naturalist David Starr Jordan described the goblin shark about a decade after the first fossil shark was found.

genus – an example, such as the duck-billed platypus or the coelacanth, of a creature seemingly changing little over time.

Opposite below right The tengu – a creature from Japanese folklore – provided inspiration for the shark’s common name.

The specifics of that idea were eventually discounted, but it’s

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89

this deep-sea shark is. In addition to senses like taste and touch, sharks have a special electromagnetic sense all their own. Jellyfilled pores called ampullae of Lorenzini run along the snout of the goblin shark, as well as sharks in general, and help the fish detect the weak electrical fields that living things emit. The electricity running through an undersea cable might have intrigued or irritated the shark – a problem that companies such as Google still have to contend with, as deep-sea sharks have bitten telecommunications cables so fiercely that it’s led to internet outages. Like many other sharks, the goblin shark bites by swinging its jaws forward and away from the base of its skull to better grip and snatch its preferred meals of rattails and dragonfishes. But this shark has taken the feeding method to an extreme, in what may be an adaptation to life as an ambush predator that can certainly make the most of some extra reach. While the shark’s jaws are snugly slotted into its long snout most of the time, making its head look like a long paddle, those jaws can jut forward in an instant. The shark has special ligaments that are usually kept under tension as the shark swims around in the dark. When the goblin shark detects prey, those ligaments relax and, as with a rubber band, they help the lower jaw spring forward extremely fast, with the upper jaws close behind. Many dead and preserved specimens of goblin sharks demonstrate this arrangement, which sometimes makes the shark look more grotesque than it truly is. No one really knows how many goblin sharks there are in the deep sea. The shark is so rarely caught, in an environment so far away from humans, that it is listed as being of little concern to conservation groups. But these fish may be highly sensitive. In 2003, over 100 goblin sharks were caught off Taiwan. No one is sure why. Some experts think an earthquake just before the record catches might have disturbed the fish. Goblin sharks have been swimming the seas for 100 million years, but we still know remarkably little about them.

Right Goblin sharks have thin, needle-like teeth best suited to nabbing slippery prey like small fish and squid.

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1,000 metres

Giant Squid The creature wasn’t supposed to exist. The creature that nineteenthcentury naturalist Japetus Steenstrup set about describing seemed like the closest thing science had found to a living legend: a giant squid.

B

y the time of Steenstrup’s study in 1857, the Age of Exploration

Despite sparking the imaginations of scientists, sailors and

was proving sensational tales of sea serpents and gigantic

the general public, the giant squid largely remained a mystery

monsters to be unfounded. All the creatures that were supposed to

for decades after Steenstrup gave the squishy animal a scientific

dwell on the margins of nautical maps were either being brought

name. Almost everything naturalists knew about the animal

into the realm of scientific inquiry or dismissed as myth. And yet,

came from corpses that washed ashore, were found dying near

time and again, stories persisted of enormous squid washing up

the surface, or were reduced to sucker hooks and beaks in the

on beaches. Ship captains sighted odd creatures near the surface

stomachs of slaughtered sperm whales. No one knew what the

that seemed awfully squid-like. By chance, Steenstrup had been

giant squid’s natural habitat was because no one had seen a healthy

able to acquire the beak of a gigantic cephalopod that had washed

one alive, much less anything else that couldn’t be gleaned from

ashore. That beak was the key. Such a specimen, made of two

decomposing carcasses. The squid seemed to live in every ocean,

keratinous halves that came together to nip and punch at prey,

and bodies kept floating up to the surface, but even as marine

was the tangible proof that gargantuan cephalopods truly dwell

biologists began to use remote operated vehicles, submersibles,

in the deep. “From all evidences,” he wrote, “the stranded animal

and even cameras attached to squid-hungry whales, seemingly no

must thus belong not only to the large, but to the really gigantic

one could catch a glimpse of Architeuthis. It took until 2005 to get the first pictures of a living giant squid

cephalopods, whose existence has on the whole been doubted.” Steenstrup gave this mythical creature a name, Architeuthis dux.

in its oceanic home. In that year, marine biologists Tsunemi

And even if other experts doubted Steenstrup’s conclusions, further

Kubodera and Kyoichi Mori debuted the first still images of a giant

proof of the enormous animal soon appeared. In 1861 the French war

squid they had photographed trying to remove some bait from a

ship Alecton was plying the waters near the Canary Islands when the

line the researchers had slipped down to a depth of 900 metres

crew happened upon a moribund giant squid floating at the surface.

(2,952 feet) below the surface. The fact that the squid actively

This was a truly enormous poulpe (octopus), so big that attempts to

tried to snag a snack – accidentally leaving a tentacle behind in

haul the entire animal aboard caused the squid’s many-armed head

the process – was useful information by itself. Biologists weren’t

to be separated from the rest of its body. All the same, there could no longer be any doubt. Somewhere out there, in the forbidding sea,

Opposite The crew of the Alecton attempt to haul the body of a giant squid on board.

there dwelled squid far larger than any found in a fish market.

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93

sure how the squid caught their meals. Some thought they were

These cephalopods can reach lengths of 12 metres (39 feet) or

active predators, like many of their smaller relatives, while others

more, and they live in every ocean at depths between 300 and

proposed that giant squid might drift along in deep-sea currents

1,000 metres (984–3,280 feet). While some researchers used to

with their tentacles extended, waiting for an unlucky morsel to

speculate that there were multiple giant squid species, genetic

blunder along. The snapshots showed that squid actively went in

analysis indicates that there is only one, global giant squid –

search of their meals, scavenging when necessary.

Architeuthis dux. Gut contents indicate that giant squid eat fish

Researchers didn’t have to wait long for additional information

and other, smaller squid, which they spot thanks to the largest

about the giant squid to surface. Other researchers from spots

eyes in the animal kingdom. Nevertheless, no matter how large

around the world began to successfully locate and film living

the squid looms in our imaginations, we barely know this

giant squid. In 2013, marine biologists at long last recorded video

celebrity cephalopod.

of a live giant squid in its natural habitat off Japan’s Ogasawara archipelago in about 700 metres (2,296 feet) of water. In 2019,

Above Most of what we know about giant squid comes from carcasses that wash ashore.

too, footage taken in the Gulf of Mexico recorded a visit from a giant squid – which briefly wrapped its arms around the Medusa

Opposite above Chart of northern Europe, 1539, with sea monsters.

camera system used by the researchers.

Opposite below Dr Tsunemi Kubodera shows the first still images of a giant squid on his laptop, 2005.

There’s still a great deal that remains mysterious about

Following pages An injured giant squid floats at the surface.

giant squid, but biologists have come to know a few things.

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GIANT SQUID

95

96

GIANT SQUID

97

1,000 metres

Cookie-Cutter Shark Sharks are well known for their big bites. Large parts of their anatomy and behaviour are based around the ways in which these cartilaginous fish capture and consume prey. And given the hundreds of shark species known, it’s no surprise that some of these species take their specializations to extremes. While only about 50 centimetres (19 inches) in length, the cookie-cutter shark has a bite that makes a great white look like an amateur.

T

he scientific discovery of the cookie-cutter shark – also

seen with odd punctures in their flesh. In fact, these wounds were

known as the cigar shark – goes all the way back to 1824.

the inspiration for a Samoan story that skipjack tuna would leave

French anatomists Jean René Constant Quoy and Joseph Paul

portions of their flesh as sacrifices when they came into Palauli

Gaimard had described the small and unusual shark as part of

Bay. In time, marine biologists picked up on the phenomenon,

a 13-volume report on the scientific findings of the 1817–20

too. Was it some kind of bacterial infection, or perhaps a parasite?

voyage of the Uranie. They originally called the shark “Scymnus”

No one could be quite sure what was creating the crescent-shape

brasiliensis for the place it was caught, off the coast of Brazil, with

wounds that looked like some sort of bite. The picture came together slowly. In 1963, ichthyologist Donald

an American ichthyologist revising the name to Isistius brasiliensis

Strasburg reported that Isistius brasiliensis does not shed teeth one

some years later. But the true nature of the shark wouldn’t become clear for over

at a time like most sharks do, but instead replaced its entire lower

a century and a half. The shark spends the day in the deep, over

tooth row all at once as if it were some kind of razor cartridge.

1,000 metres (3,280 feet) down, and comes much closer to the

Strasburg wondered what kind of lifestyle could necessitate such

surface at night. Given that the fish spent almost all of its time

a strange adaptation that allowed the little shark to always have a

in the darkness and was practically impossible to observe in life,

perfectly even set of large, sharp teeth. The answer would come

no one really knew how it sustained itself – or its connection to

in 1969, during a strange moment of discovery aboard the R/V

strange wounds found on various sea creatures.

Townsend Cromwell as it trawled the Pacific for deep-sea fish.

Despite a great deal of time spent at depth, the cookie-cutter

The nighttime trawls brought dead and dying cigar sharks

shark seems to prefer warmer latitudes in the world’s seas around

to the surface. Marine biologist Everet Jones was on board and

the equator. And in these waters, larger fish and dolphins could be

recalled Strasburg’s question about the shark’s teeth and the

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)teuthisgemm ato

COOKIE-CUTTER SHARK

possible connection to the mysterious wounds on fish and whales.

another for its food without making a permanent attachment to

Jones remarked on the idea to research assistant John Fowler, who

or killing the host. This makes the cookie-cutter shark a kind of

then took a nearly dead cigar shark and pressed its mouth against

flesh grazer, taking chunks out of various animals but not causing

the side of a dead fish to see if the shark might bite with a reflex

debilitating injury in the process.

action. The shark did, and scooped out a crescent-shaped wound

Naturally, the way the shark feeds has been its biggest claim

just like the ones that had so mystified scientists. The researchers

to fame. But that’s hardly all. The cookie-cutter shark is also

had their culprit, and closer inspection of photographed wounds

bioluminescent, and, in fact, might have the most intense

on tuna, whales and swordfish matched up with the teeth of the

underwater glow of any known shark. The photophores that

cookie-cutter.

create light on the shark’s body – a kind of camouflage that

Marine biologists have learned a great deal more about the

disrupts the shark’s silhouette against would-be predators – can

cookie-cutter shark since that first nighttime experiment. These

continue to shine for hours after death. In habitats where light

sharks are not especially strong swimmers, and, alone or in small

rarely reaches, a little glow can help disguise the cookie-cutter.

schools, practically hover in the water column as they wait for large prey to pass by them. When the cookiecutter strikes, the shark uses a specialized set of lips to briefly suck on to the surface

Top left The cookie-cutter shark is also known as the “cigar shark” for its small size.

of its prey and quickly bite down to scoop out a large chunk of skin, blubber, muscle, or whatever else it can get a mouthful of. Zoologists call this way of feeding facultative ectoparasitism,

Above left The triangular teeth fit in an almost razor-like arrangement and are shed all at once instead of one by one.

to describe when an organism is specialized to rely on part of

Above right The formidable bite of the little cookie-cutter shark.

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1,000 metres

Giant Oarfish In mid-October 2013, a strange fish washed up on Oceanside Harbor beach on the California coast. Almost 4 metres (13 feet) long, the sinuous creature was quickly identified as a giant oarfish – the longest bony fish in the sea. Thought to be the inspiration for some tall tales about sea serpents, the fish is so big and so rarely seen that it’s a living legend.

T

here are at least two species of oarfish in today’s oceans. The

straight and propelled itself by undulating the long, red dorsal

smaller of the two, the streamer fish, lives at depths below

fin atop its back. This is called amiiform locomotion, similar to

below 500 metres (1,640 feet) and has a ribbon-like ornament

that used by freshwater bowfin fish. Then again, giant oarfish

jutting from its head. But it’s the giant oarfish that often makes

have also been seen swimming vertically, perpendicular to the

headlines when it’s seen, a huge and sinuous fish that is still

ocean surface. Precisely why they move this way is unclear, but

poorly known.

when you spend your entire life underwater with thousands of metres/feet of depth, there are many different directions and

Called Regalecus glesne by specialists, the giant oarfish is an

ways to move around.

open-water species. The largest verified individuals get to be 8 metres (26 feet) long, though there are rumours that 11-metre

Much of what marine biologists have been able to discern

(36-foot) oarfish have been seen, as well. The individuals that

about giant oarfish comes from individuals that become stranded

wash up on shore are actually far from their usual home. These

or wash ashore. The fish is toothless, with more than 40 gill

fish live deep below the surface of the open sea, up to 1,000 metres

rakers inside its throat to help filter out small plankton and other

(3,280 feet) down and across a broad range of the world’s tropic

morsels from the water column. Gut contents from stranded fish

and semitropic oceans. The fish’s preferred depth – like many

indicate that they eat shrimp, jellyfish, small squid and other tiny

deep-sea organisms – makes it challenging to study. Despite

prey. And despite what you might think for a fish of such length,

being named in 1772, the first camera footage of a giant oarfish in

most vital organs in the giant oarfish are crammed close by the

its home habitat didn’t surface until 2010.

head and so the majority of the fish’s body is tail. This might be a

The fish is so seldom seen that marine biologists aren’t even

defensive adaptation. If a shark or other ocean predator were to

entirely sure how the sinuous giant moves through the water

attack, the oarfish would be able to survive if it lost a little bit of

column. One oarfish spotted in the Bahamas kept its body

its tail.

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GIANT OARFISH

Top Giant oarfish are immediately recognizable from the bright red “mane” running along their backs. Above Giant oarfish live too deep to be found easily. Marine biologists have had to learn a great deal from stranded specimens, like this fish discovered by a US Navy installation in 1996.

101

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GIANT OARFISH

Despite the potential dangers, the giant oarfish is best adapted

into the ocean plankton. From there, it’s a matter of luck. Many

to life in the deep sea. Oarfish seen near the surface, despite

of the eggs will be eaten by other creatures that inhabit the deep

making a striking impression upon any people who might spot

ocean. But the few that manage to hatch will be tiny ribbons that

them, are often sick or dying. The surface waters are a harsh

dwell just below the surface, where they can suck up detritus and

place for these fish. Down deep, there are no strong currents

plankton smaller than themselves. They swim with long pectoral

to buffet the fish about and so they don’t develop the kind of

fins – not the iconic dorsal fin seen in adults – and their mouths

sturdy musculature that would allow them to navigate the

stay open to take in any nutritious specks they need to grow. It’s

more turbulent waters near the surface. The relatively calm and

only as the oarfish mature and become larger that they begin to go

consistent conditions through the deep sea, across latitudes and

deeper, and are rarely seen at the surface again.

longitudes, may be what allow this fish to range worldwide, but at restricted depths.

Opposite Gut contents from giant oarfish washed ashore often contain jellyfish, squid and shrimp.

But these ocean giants start off life very small. When giant oarfish spawn, which may be several times over the course of a

Above Juvenile oarfish spend much of their time near the surface feeding on plankton, only inhabiting greater depths as they grow larger.

month or two, the fertilized eggs from the female fish drift out

103

1,500 metres

Lanternfish Sonar technicians were confused by the readings. During the Second World War, as navies began to use sound to navigate the deep sea and detect submarines, the operators listening in kept finding that the seafloor was in the wrong place – and that it moved. In daylight hours the sea bottom seemed to be up to 500 metres (1,640 feet) deep, yet at night the same readings were coming up closer to the surface.

B

oth seemed wrong compared to oceanic surveys, until

per cent of deep-sea fish biomass is lanternfish – more than 550

researchers realized that what they were reading as the

million tonnes of these sleek little swimmers.

seafloor wasn’t really the bottom at all. They had found the

Lanternfish have been around for a very long time. Tiny, hard

deep scattering layer – not so much a level of the ocean but of

structures that aid fish in hearing and balance – called otoliths –

innumerable small creatures, including millions and millions

have allowed palaeontologists to track the origin of these fish back to

of fish. The air-filled swim bladders of these little fish were

more than 55 million years ago. Back then, the ancestors of today’s

causing the sonar signals to be misread, and many of these tiny,

lanternfish didn’t dwell in deep water. Their remains are found over

confounding swimmers were lanternfish.

the continental shelf, in relatively shallow water. It wasn’t until about

Known to experts as myctophids, lanternfish get their name

33 million years ago that lanternfish started going deeper, their

from the fact that these fish bioluminesce. The placement of their

otoliths appearing in deeper sediments. Even then, these fish weren’t

glowing tissues varies from species to species, ranging from the

behaving like their modern counterparts. The daily migration of

underside of the belly to the tip of the snout. And there are a

lanternfish from deep to shallower waters didn’t start until about

lot of these fish. Marine biologists have counted more than 246

15 million years ago, a time when changes to nutrient cycling in

species since the late nineteenth century, ranging from 2 to 30 centimetres (¾ to 11¾ inches), and these fish might be the most

Opposite Lanternfish get their name from the prominent bioluminescent organs along their bodies.

numerous vertebrates on the planet. Experts estimate that 65

104

LANTERNFISH

105

106

LANTERNFISH

the oceans allowed plankton to bloom and provide ample food for

placements are likely to act as camouflage – causing the fish to

creatures ranging from whales to the tiny lanternfish.

look darker from above and lighter from below – others help these fish keep to schools of their own species or allow the fish to

Much like the megamouth shark (see pages 40–43) and other

find mates in the darkness.

deep-sea creatures dependent on plankton, lanternfish spend daylight hours down deep. Many lanternfish swim through the

In fact, having such a unique and malleable way to communicate

dark of the Twilight Zone and into the Midnight Zone, between

might explain why there are so many species of lanternfish

300 and 1,500 metres (984–4,921 feet) below. But because these

compared to other deep-sea fish species. The deep sea is more

fish feed on tiny zooplankton, they need to follow the food. As

like a void than any environment on land. There aren’t as many

their preferred morsels rise towards the surface at dusk, the

geographical barriers that cause populations to become divided

lanternfish follow. This migration also means the small and

and evolve in different ways. But the way lanternfish communicate

abundant fish have less risk of becoming meals themselves. Not

with each other allows for other evolutionary pressures – like

that all lanternfish follow this pattern. Some reside in the deep for

sexual selection – to play a role and generate a greater number of

almost their entire lives. And it iss these differences that may have

unique species. When lanternfish want to attract or communicate

spurred lanternfish to evolve their characteristic illumination.

with members of their own species, their light can be seen from

If lanternfish only used their bioluminescence to blend into the

about 30 metres (98 feet) away, a form of deep-sea advertisement

sea or avoid predators, then we might expect most species to have

that these swimmers have mastered. If you see a light in the ocean

similar arrangements of photophores to best distract or deceive.

deep, chances are it’s a lanternfish.

But that’s not the case. Diaphus lanternfish have photophores near Opposite Lanternfish are considered to be one of the most common deep-sea creatures, making up about 65 per cent of all the deep-sea fish biomass.

their eyes, often likened to headlights, while others have glowing spots near their fin bases or under their bellies. The light can be yellow, blue or green, and sometimes the details of their light

Above Different lanternfish species have various arrangements of photophores, suggesting that some of these bioluminescent organs are for communication as well as camouflage.

patterns differ between males and females of the same species. All this diversity is an important clue. While some photophore

107

1,500 metres

Big Red Jelly Sometimes new deep-sea species are hiding in plain sight. That’s how the big red jelly Tiburonia granrojo was discovered – not through immediate recognition but through careful scientific detective work.

I

n 1998, marine biologist George Matsumoto got a call about a

own evolutionary group, the Tiburoniinae, and the name comes

strange jellyfish that had been seen on an underwater geology

from the name of the remote operating vehicle the 1998 geology

expedition. This isn’t all that unusual. Scientists with varied

crew was using, the Tiburon (meaning “shark”). To date, the

backgrounds study and explore the deep sea, and sometimes a

jellyfish has been seen in deep waters off California, the Hawaiian

crew looking at one phenomenon – such as the geology of the

Islands and Japan. With such a broad range, the big red jelly might

ocean floor – spot unusual creatures or phenomena they need help

show up in other places, too. If Tiburonia does appear on other dives around the world,

to identify. In this case, the geology crew spotted a large, reddish

marine biologists should be able to identify it pretty readily. First

jellyfish that didn’t seem quite like any known to biologists. Matsumoto thought the jellyfish might be new, but proclaiming

of all, Tiburonia is very large. The bell of this jelly can span 1 metre

a new species is not as easy as it was in the eighteenth and

(3 feet 3 inches) across and the entire animal is a deep, vibrant red.

nineteenth centuries. Marine biologists have to comb through

Stranger still, the big red jellyfish doesn’t have any tentacles. That’s

the literature to make sure no one has previously described the

especially odd, because most jellyfish – at least those familiar to

same animal, even offhandedly, and compare the anatomy and

us from the seaside and aquariums – have tentacles and oral arms

behaviour of the mystery species to what’s already documented.

equipped with specialized stinging cells trailing beneath their

In this case, Matsumoto and his colleagues didn’t just have a paper

bell. When an unlucky fish swims into the oral arms, harpoon-like

trail to pore over to see if anyone else had seen this jelly, but also

stingers pop out and injure or incapacitate the fish with venom as

15 years of videos taken during deep-sea explorations.

it is drawn upwards towards the mouth. But Tiburonia is different.

Others had. Researchers had sighted Tiburonia by 1993, at least,

Rather than having oral arms and stinging cells, Tiburonia

but no one had taken particular interest in it at the time. Perhaps

instead possesses between four and seven flexible and fleshy arms

they didn’t quite realize what they were seeing. After extensive

that likely allow the jellyfish to grasp its food. What that food is,

research, Matsumoto and colleagues were able to discern that

though, is as yet a mystery, but it’s likely to be small morsels that

Tiburonia granrojo – or “big red” – really is a unique jellyfish that

are more readily available at depth.

lives between 650 and 1,500 metres (2,132–4,921 feet) down. In

Watching Tiburonia move through the water is an almost

fact, it’s so unlike other jellyfish that the species was placed in its

hypnotic experience. Like other jellyfish, the big red jelly primarily

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BIG RED JELLY

moves by flexing and relaxing rings of muscle within its large bell.

even some that have previously been seen but not recognized as

The arms flex and undulate beneath, the entire animal seeming to

unknown. Tiburonia was seen at least as far back as 1993, came

move in slow motion.

to scientists’ attention in 1998, and was formally named in 2003. How many other possible new species have been seen in that

Despite being seen multiple times and in many parts of the

same time-frame but await their scientific recognition?

ocean, there’s still much that remains unknown about this deepsea giant, and only one specimen has been collected for study at the surface. But the new species was also a reminder to scientists that

Above The big red jelly was seen several times by undersea explorations before it was conclusively identified as a new species.

the deep sea is still full of organisms awaiting discovery – perhaps

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1,520 metres

Viperfish Life in the deep sea can often seem foreboding. It’s a cold, dark place where bizarre creatures float and drift through the water column. Some even have nasty-looking teeth, like the sleek viperfish

Chauliodus. But when you get past the fish’s shock value, you can see that the viperfish is a predator that is just as beautifully adapted to its role in the undersea ecosystem as any brightly coloured reef fish.

F

rom a photo or video brought back from an underwater exploration, viperfish might seem menacingly enormous.

In truth, these predators are pretty small. The Pacific viperfish, Chauliodus macouni, is only about 30 centimetres (11 inches) long. Unlike anglerfish and some other deep-sea hunters, these fish are not after prey larger than themselves. Instead, viperfish tend to feed on small squid, fish, crustaceans and worms. Rather than using their needle-like teeth to impale squirming prey, viperfish use a different strategy. The teeth of viperfish are extremely long. In fact, the teeth don’t really even fit inside their mouths – part of what contributes to their striking appearance. If the fish were to impale small prey on their teeth, then, those meals might actually be inaccessible, as they’d be stuck outside the mouth. Instead, viperfish open their mouths extremely wide to surround and engulf the shrimp, squid and other prey, their teeth forming a kind of net that prevents prey from escaping. The teeth are also firmly attached to the jaw and are not flexible, which requires these fish to have the impressive gapes they do. Even though viperfish aren’t biting into their prey so much as trapping and swallowing it, these fish have still evolved some key

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VIPERFISH

Opposite The teeth of viperfish are not meant to impale prey so much as form a net to prevent small prey from escaping. Above Viperfish can open their jaws extremely wide, over 90 degrees.

111

adaptations to assist their way of feeding. The first vertebra in the fish’s spine, just behind the skull, has been modified to act as a kind of shock absorber to help prevent viperfish from injuring themselves from the incredible forces of opening their jaws wide – to about a 90-degree angle – and quickly slamming them shut. Even though researchers have calculated that viperfish are able to eat prey up to 63 per cent larger than themselves, and have even been photographed with bellies distended by huge prey, there’s no evidence that these fish typically go after such hearty meals. Much like the gulper eels (see pages 122–125), the wide gapes of these fish have more to do with their strategy for nabbing large amounts of small prey. Studies of Chauliodus sloani, a viperfish found from the Atlantic to the Mediterranean Sea and Pacific, has been found to principally feed on lanternfish (see page 104–107). Experts estimate that viperfish need to eat about one lanternfish every 12 days to survive – not too difficult given the sheer abundance of the flashing little fish. Rather than following lanternfish or other prey up and down the water column, researchers think that viperfish stay in darker depths and generally lie in wait for prey to come close to them. If lanternfish don’t come by, fish eggs or even algae will do. But the viperfish must also be wary. There are bigger and hungrier animals in the deep, some of which consider viperfish food. Viewed in the dark, the bellies of viperfish might seem to light up as if they are runway lights. Like many other deep-sea creatures, these photophores camouflage the viperfish by way of counterillumination. Their light undersides help the fish hide – to a predator lurking below, the undersides of viperfish blend in with the lighter waters above. Some species have photophores on their fins, too, which probably act as social signals that let these fish find each other when it’s time to mate. Like lanternfish and vampire squid, viperfish also have a fossil record. Fossil viperfish have been found in rocks more than 5 million years old in both California and Russia. The fossil from Russia, in particular, resembles the living species Chauliodus macouni, albeit with a few differences in the spine and body proportions. It’s possible that there are other fossil viperfish out there that might help fill in their long history, but the particulars of how deep-sea fossils are formed and become exposed (see page 35) means that – as with deep-sea coelacanths – such finds are relatively rare. Right Despite the terrifying appearance, viperfish are relatively small and use photophores to hide from larger predators.

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VIPERFISH

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1,674 metres

Whalefalls In 1987, during a deep dive off southern California’s Catalina Islands, the crew of the DSV Alvin discovered an ecosystem that no human had ever seen before. Deep down, over 1,200 metres (3,937 feet) below the surface, the team spotted the bones of a large whale resting on the seafloor.

B

ut this was not simply a whale carcass that had sunk to the

scavengers such as sleeper sharks and large crabs pick at whatever

depths and fallen apart. The bones supported an entire

flesh remains on the whale. This period of skeletonization can

ecosystem of creatures that lived off the dead whale’s largesse –

last between a few months to several years depending on where

from slinky hagfish feeding on scraps of flesh to strange new worms

the whale’s body lands and what species live in the area. These

that bored into the very bones of the whale. This was not just an

scavengers are usually itinerant and are feeding on a glut of food

ocean oasis, the researchers realized, but an entire ecosystem based

that almost literally fell into their laps. In fact, there’s so much

around the carcasses of deceased cetaceans. They came up with a

to feast on that even a mostly denuded whale still has plenty of

special name for these peculiar and temporary habitats: whalefalls.

scraps and oil for scavengers in the second stage. During this

Whalefalls are defined by the very creatures that have given

enrichment opportunist phase, snails, crabs, worms and other

their names to the phenomenon. Across the seas, where whales

invertebrates pick at whatever tissues remain and often burrow

live and migrate, whalefalls form. Marine biologists have learned

into the sediment under the whale’s increasingly exposed bones. The third stage is what makes whalefalls unique. Researchers

a great deal about them since 1987. Each whalefall goes through a series of stages. When a whale

have named this the sulphophilic stage, a period when bacteria

perishes, blubber and gases from decomposition cause the whale

start to break down fats and oils inside the whale bones. The

to float at the sea’s surface. As sharks and other scavengers feed

process creates a great deal of sulphur which, in turn, helps feed

on that carcass, the whale’s blubber begins to be eaten away and

more bacteria and the creatures that feed upon them. There are

the decomposition gases escape. The whale sinks. This is the start

also some worm species – known as Osedax – that happen to land

of a whalefall community.

on the whale’s bones and burrow in, secreting acid to break down and feed on the whale’s skeleton. This stage can last half a century

During the first stage, called the mobile scavenger stage, sizeable

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WHALEFALLS

Top Whalefalls go through several stages that are marked by what organisms are feeding on the carcass, from “mobile scavengers” to bacteria that feed on sulphur. Above Whalefalls can occur at a variety of depths, from the shallows to the deep sea.

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WHALEFALLS

and is usually followed by an indeterminate reef stage during

The antiquity of whalefall organisms and communities

which encrusting organisms settle and grow on the whale’s bones.

indicates that these ecosystems have formed around various

Experts have learned so much about whalefalls that they’ve

seagoing animals through long periods of time. It would seem

actually been able to identify that the phenomenon predates

that whalefalls started as more general deadfalls of large marine

the earliest seagoing whales by millions upon millions of years.

reptiles that drifted down to the sea bottom. And even though

The first whales evolved about 55 million years ago, but lived

many of these marine reptiles went extinct at the end of the

on land or were amphibious. It wasn’t until about 40 million

Cretaceous period, 66 million years ago, some lineages survived.

years ago that whales were living full time in the oceans. Yet

Sea turtles persisted through the mass extinction and, researchers

palaeontologists have found evidence of bone-boring worms

speculate, these reptiles helped deadfall communities survive in

and whalefall-like communities in even older rock strata dating

the millions of years between the mass extinction and the first

to the Age of Reptiles.

wholly aquatic whales. The repeated evolution of seafaring

Around 235 million years ago, during a time period called

vertebrates formed the basis of a still-mysterious ecosystem that

the Triassic, many forms of reptiles started to adapt to life

has existed for over 100 million years but was only discovered

at sea. These lineages included the ancestors of the fish-like

in 1987 – a reminder that the deep sea still has many secrets to

ichthyosaurs, the long-necked plesiosaurs, and sea turtles, all

dredge up from the dark.

of which thrived through the Mesozoic in the millions of years

Opposite above Peculiar worms called Osedax are often found in whalefalls, leaving tell-tale burrows in the exposed bones.

that followed. And, it seems, these creatures formed the basis of early whalefall communities long before the origin of whales. In

Opposite below Hagfish are found at whalefalls in the early stages, feeding on the carrion clinging to the bones.

2015, for instance, palaeontologists described damage created by Osedax-like worms on the bones of sea turtles and plesiosaurs

Above The bones of some plesiosaurs have been found with the same signs of burrowing worms and other creatures found at whalefalls today.

found in 100-million-year-old rocks.

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1,700 metres

Hagfish Evolution is often presented as a story of progress, of creatures becoming more complex and adding new features through time to keep up with an ever-changing planet. But that’s an illusion. Evolution has no inherent drive to be bigger and better, and, in fact, sometimes major adaptations or anatomical breakthroughs are reversed. Hagfish are a great example of this: despite being vertebrates, these fish have almost entirely lost their backbones.

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ven though they are often spoken about as if they were just one strange species, “hagfish” actually refers to several

different groups of archaic fish in a family called the Myxinidae. Exactly who these snake-like swimmers are mostly closely related to has been something of a headache for biologists. Hagfish don’t have jaws, and so early classification schemes placed them close to the jawless lampreys on the tree of life. Both were thought to be leftovers from truly ancient times, hundreds of millions of years ago, before jawed fish evolved. But more recently, researchers have questioned this view, especially because hagfish appeared to lack any vertebrae – a trait that lampreys have. The new scheme put lampreys closer to vertebrates –

can detect light and dark but little else, which makes sense for

including humans – while hagfish seemed to represent something

creatures that spend their entire lives in the ocean dark. For a

much more primitive. But fossil, genetic and anatomical evidence

long time, it was thought that such rudimentary eyes meant that

changed the picture again. Despite their differences, lampreys and

hagfish were extreme survivors from the earliest days of vertebrate

hagfish truly are close relatives. The strange traits in the hagfish

evolution. But the discovery of fossils of hagfish from over 300

are evolutionary reversals, undoing some previous adaptations,

million years ago indicates that hagfish used to have complex

making these fish seem much more archaic than they actually are.

eyes capable of seeing far more. The change likely has something

Look at the strange, pink face of a hagfish and you won’t find

to do with a shift towards deeper, darker environments where detecting light is not as critical for survival.

any eyes. In fact, only some hagfish have eyespots – pinholes that

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HAGFISH

Opposite Zoologists have debated for decades where hagfish fit into the tree of life, with recent analyses hinting that hagfish are vertebrates. Above Lampreys are jawless fish that are closely related to – though significantly different from – hagfish.

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HAGFISH

The various changes have made modern hagfish easy to recognize at a glance. Most are around 50 centimetres (1 foot 7 inches) long, with the largest getting to about 127 centimetres (4 feet 2 inches), and all have long, sleek bodies tipped with an oar-like tail fin. The anatomy of hagfish gets even stranger on the inside. They don’t have a full spinal column, but rather remnants of vertebrae around a flexible notochord (considered the forerunner to the backbone) and their skulls are almost entirely made of cartilage. Although hagfish have no jaws, they do possess tooth-like structures in their mouths made of keratin, the same stuff your fingernails are made of, and use these to help grasp food and pull it inwards. As if all that weren’t remarkable enough, hagfish are famous for their slime. Along the sides of hagfish are dozens of little pits, or invaginations, that house slime-producing glands. The slime itself it full of proteins and extremely sticky, viscous enough to muck up the gills of a predatory fish that might want to take a bite. And even if such a predator gets a hold, hagfish can tie themselves into a slipknot, the friction scraping the mucus off their skin and into the face of their attacker. Not all hagfish live deep down. Some prefer the shallows. But others can be found over 1,700 metres (5,577 feet) below the surface – cold and dark environments where hagfish sift sandworms from the bottom or strip small pieces off whalefalls. Hagfish may even burrow into big carcasses that sink from above, using the same slipknot technique they use to evade predators to bust up rotting flesh into more manageable and consumable pieces. And if such food is unavailable, hagfish are soft enough that they can absorb organic material through their skin – a way to obtain enough to sustain them in environments where opportunities to feed may only come around once in a while. What researchers have slowly realized about the strange nature of the hagfish is a reminder that not every organism that looks primitive or has traits in common with prehistoric species is a “living fossil”. Fossil hagfish don’t always look like their modern counterparts, and some of the most distinctive features of hagfish evolved more recently as the fish found a home in deep water and then wiggled into shallower habitats. The strange little fish is a potent reminder that life doesn’t always unfold as we expect – sometimes what’s old becomes new again. Left Hagfish have a unique feeding ability. Once they burrow into a carcass, they can tie a knot along their tail and work that knot forward to break off bite-size pieces of flesh.

121

1,800 metres

Gulper Eels Food can be hard to find in the deep sea. Dark waters can make tracking prey problematic – especially when they have bioluminescent defences to camouflage and confuse – not to mention the simple difficulties of finding potential meals in a vast, three-dimensional void. Deep-dwelling organisms often have to make good use of whatever passes by or floats down from above, and so it’s no surprise that some fish have evolved ways to make the most of every meal. With mouths bigger than the rest of their bodies, gulper eels open wide to make the most of the deep-sea menu.

T

echnically known as saccopharyngiformes by marine biologists, gulper eels are typically found between

500 and 1,800 metres (1,640–5,905 feet) below the surface. Experts have known about them since the nineteenth century, yet relatively little is truly understood about these long, bigmouthed fish. Adults are rarely seen, and those that are trawled to the surface, or otherwise collected, tend to be so delicate that it’s difficult piecing together their natural history. These fish are not quite like any others. As a group, gulper eels lack many of the characteristic features that marine biologists expect to see on a fish. Gulper eels don’t have any ribs, for example, nor do they have air-filled swim bladders to help them maintain neutral buoyancy. Even their

Above The pelican eel Eurypharynx pelecanoides has a specialized, light-emitting organ at the tip of its tail.

muscles are unusual. In most fish, blocks of muscle have a characteristic “W” shape, while gulper eels have V-shaped muscle

Opposite above Gulper eels are easily-identified by their enormous mouths at the front of relatively thin and sinuous bodies.

segments. And that’s to say nothing of their mouths. At a glance, gulper eels are mostly mouth with a thin, sack-like body and a

Opposite below The eel’s big mouth might be an adaptation to eating lots of small creatures, similar to how baleen whales filter food.

long, trailing tail behind.

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GULPER EELS

One of the better-known gulper eels is the pelican eel,

the body. But that’s not the case with the pelican eel. Its lower jaw

Eurypharynx pelecanoides. This fascinating fish was named back in

seems to simply hang free of the rest of the body, a loosely hinged

1882, yet is still seldom seen by marine biologists. Part of what

joint that can open incredibly wide.

makes this eel look so unusual is the way its jaws are set up. In

While the size of its mouth has sometimes been taken as an

many fish, the lower jaw is in front of and connected to the rest of

indication that the fish must be eating large prey – whatever

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124

GULPER EELS

can fit inside the gaping maw – gut contents from pelican eels suggest a different strategy. These eels are not menaces that regularly gulp up entire struggling fish, but instead may be filterfeeders. Pelican eels are often found with small crustaceans in their stomach. No one has definitively documented how these fish feed, but, based on stomach contents, marine biologists hypothesize that gulper eels regularly swim through aggregations of shrimp, amphipods, or other crustaceans and open their jaws like a net to catch as many as they can – not unlike a baleen whale feeding on shoals of fish. While pelican eels certainly can and do swallow larger fare, such as deep-sea squid, the core of their diet may be many tiny invertebrates that they capture in bulk with their net-like maws. A great deal of what marine scientists know about gulper eels comes from dead specimens that are caught at depth and brought to the surface – many deep-sea organisms, adapted to the cool and pressure of the deep, don’t fare well in the upper zones of the ocean. It wasn’t until 2018 that marine biologists were able to observe a gulper eel searching for food near the Azores, indicating that these eels hunt rather than simply waiting for prey to come their way. Still, what researchers have witnessed only answers one question among many. There are still many aspects of these eels’ lives and biology that remain poorly known or seem to hint at tantalizing possibilities that have yet to be verified. While the mouth of pelican eels has garnered much attention, there is also a mystery at the other end of this particular gulper eel species. At the termination of the fish’s whip-like tail is an unusual organ made up of small tentacles that glow pink and can flash red. No one knows what this organ does for the eel or precisely why such a structure evolved. One possibility is that the light helps attract prey, but then the eel would have to take a strange and as-yet-unseen posture to bring its mouth close enough to its tail. It’s more likely that the tail has some other function, a mystery that can only be solved through luck and time in the realms where these eels sinuously swim.

Left The stomachs of gulper eels, such as this Saccopharynx lavenbergi, can expand to accommodate whatever food they come across in the deep sea.

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1,800 metres

Orange Roughy The deep sea can feel like a distant and forbidding place, a world of darkness where strange squid flash and slow-moving sharks patrol. But there are some elements that are familiar and can even be found on the dinner table. A peculiar fish called orange roughy is one of these ties between the land and deep waters, a culinary connection that has raised big questions about how we can better preserve life that lives deep down.

A

lso known as red roughy, the deep sea perch, and the less-

go is red. Anything red at the top of the Sunlight Zone – whether

than-flattering “slimehead”, orange roughy are known to

a wetsuit or a fish – will look darker and darker with depth. In

experts as Hoplostethus atlanticus. These fish can be found between

fact, a fish that is red at the surface will likely look pitch black at

180 and 1,800 metres (590–5,905 feet) in spots as distant from each

the boundary of the Sunlight and Twilight Zones, and so many

other as the coast of Iceland to the waters off Chile. The term “red

deep-sea fish and other species are technically red because they

roughy” might be the most apt, as they are a deep red colour when

appear as nothing but shadows in their natural habitat. One of the other names for the orange roughy – the slimehead –

alive, but fade to yellow or orange when brought to the surface. The deep red of the living fish might be a form of deep-sea

comes from the mucus they excrete. Many fish have a lateral line that

camouflage. At the surface, sunlight contains all the colours in

runs from the head to the tail, a series of pits that act as pressure and

the visible spectrum. But with depth, the energy from sunlight

vibration detectors. Lateral lines allow fish to school, for example,

decreases and different wavelengths within the spectrum begin to

as they can feel how their neighbours are moving. In the case of

disappear. Blue and violet are among the last to fade, but first to

the orange roughy, though, those sensory pits include muciferous

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ORANGE ROUGHY

canals – small pores that ooze mucus. The precise function of their

going on to hatch, and a fraction of those growing large enough to

slime isn’t clear, but it might be related to the orange roughy’s ability

avoid being eaten by plankton-focused predators, and so on. Even

to sense motion in the water and evade predators.

though orange roughy can live to be about 200 years old, their

Rather than living in the open void of the deep sea, orange

slow reproduction has made them especially vulnerable to the

roughy are demersal – a term for animals that live along or

overfishing that has caused their populations to crash.

near the sea bottom. The fish seem to show a special fondness

Prior to the 1970s, when the fish was primarily called the

for undersea canyons, rises and other geological features, where

slimehead, orange roughy was not on the menu. But researchers

they often rest between searching for food. In fact, during these

discovered what seemed to be large schools of fish that were

rest periods the fish temporarily fade in colour and simply float,

easily caught off New Zealand. The fish started to make their

almost oblivious, which may be a way to conserve energy and

way to market, with the US National Marine Fisheries Service

needed resources in between feeding forays.

rebranding the fish as orange roughy and marketing them as a

Orange roughy live life in the slow lane. These fish take about

new source of seafood that appeared to be abundant. But no one

20 years to reach sexual maturity, at which time they spawn for

at that time knew just how long it takes these fish to reproduce,

a few weeks each summer. Even so, they don’t produce as many

which turned this species from an “underused” fish to one that is

offspring as other fish species. Even though the numbers might

now considered vulnerable to extinction even as it still appears

seem high to mammals like us, the fact that female orange roughy

on dinner plates.

typically produce about 22,000 eggs per kilogram of body weight is actually low compared to other fish. A 5-kilogram (11-pound) orange roughy will release about 110,000 eggs. Of that pool, only

Opposite Orange roughy have multiple pores that secrete a mucus-like substance, which gives them the alternate name “slimehead”.

a fraction will be fertilized, with a tiny proportion of those eggs

Above Freshly landed roughy from a deep-sea trawl.

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2,000 metres

Brachiopods In fiction and fantasy, the deep sea is often thought of as a refuge for bizarre, ancient species. The idea isn’t all that far off the mark. Creatures such as the goblin shark, the vampire squid and the coelacanth are all modern creatures that have close fossil relatives and seem to inhabit peculiar niches which last much longer in deep-sea habitats than in waters near the surface.

B

In whatever way brachiopods got their start, they were an

ut not all of these modern relatives of prehistoric wonders are quite so immediately astonishing. Though easy to take for

evolutionary hit. Palaeontologists have named over 12,000 distinct

granted, it’s a wonder that brachiopods still live in the deep ocean.

brachiopod species so far. They are sometimes so numerous and

At first glance, a brachiopod might look quite a bit like a

so specific to particular slices of geologic time that experts rely

mussel or a clam. These animals also have soft bodies held safe

on brachiopods for an entire science called biostratigraphy. The

within shells with two halves. But while many familiar seashore

concept is simple. Brachiopods were abundant and diversified

creatures are bivalves – usually having two equally sized shells

readily, meaning each species existed within a confined span

that are joined together – brachiopods are different. These

of time. If a palaeontologist finds a particular species in rock on

animals have one shell, or valve, that is larger than the other, and

one side of a valley, then they can look in the rock layers on the

have their hinge at the rear end. They’re sometimes called “lamp

other side for the same species to determine which rock layers go

shells” for their resemblance to the oil lamps of Ancient Greece.

together and represent the same time period. This can be done on a

As a group, brachiopods are very ancient. The earliest

global scale as well, and combined with absolute dating techniques

known brachiopods date all the way back to the early part of

to determine a prehistoric timeline in places where it might not

the Cambrian period, more than 530 million years ago, when

otherwise be possible. If absolute dating techniques indicate that a

animal life was a new phenomenon on Earth. Precisely what organisms brachiopods evolved from is still being investigated by palaeontologists. At present, it seems that brachiopods are related

Opposite Brachiopods belong to an entirely different group of molluscs than clams or mussels, defined by having two shells of different sizes.

to creatures called phoronids – which still live in the seas – that support their soft bodies with a sheath of hardened keratin.

128

BRACHIOPODS

129

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BRACHIOPODS

brachiopod lived 200 million years ago, for example, then experts

living brachiopods. The deep sea is not necessarily a bad place

can hypothesize that any ancient environment in which the same

for brachiopods to take hold. They can survive on little food,

species is found is about 200 million years old – handy when a rock

using a specialized organ called a lophophore – or a bunch of

layer might be difficult or impossible to get a direct date from.

small tentacles – to circulate water through their shell and sieve

Brachiopods were incredibly successful for about the first 280

out their food. They don’t have to move much or find prey.

million years of their history, during the Palaeozoic era – or 541

Brachiopods can simply sit on or in the sea bottom, circulating

to 251 million years ago. Ancient reefs were sometimes built

the water to extract the food they need.

primarily by brachiopods, and many of these ancient species were

Deep water seems to suit brachiopods. Many of them are found

filter-feeders that strained plankton and detritus from the water.

in places where there is some sort of shelter from rough water

But the worst mass extinction of all time cut back the brachiopods’

or turbulent currents. Without sunlight or interference from the

success. Around 252 million years ago, intense volcanic activity

waves above, brachiopods can readily make a home at depth –

caused the climate to rapidly warm, the oceans to acidify, and

often populating the same spot for so long that young brachiopods

atmospheric oxygen to drop. The effects reached far into the seas

sometimes grow atop the shells of older ones. Perhaps it’s not the

and, though they survived, brachiopod numbers would never be

most dramatic lifestyle for creatures that have been around since

as abundant as they once were.

the dawn of animal life, but it’s worked for them.

Still, brachiopods have hung on even as bivalves have become much more common. You can still find them, if you know what deep ocean floor. To date, about 63 species of brachiopods live

Opposite Brachiopod fossils are important touchstones for palaeontologists. They are so numerous that experts can track evolution and extinction across time by studying these ancient shells.

at depths below 2,000 metres (6,561 feet) – about a third of all

Above Brachiopods have existed for over 541 million years.

to look for, from the shallows to the continental shelf to the

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2,000 metres

Anglerfish Much like the giant squid, anglerfish are iconic creatures of the deep. Few animals seem to encapsulate the nature of their environment quite like these toothy, bioluminescent fish that look like little more than swimming mouths. Yet, as researchers have gotten to know them, these fish have proved remarkable examples of how life can adapt to suit extreme and stringent conditions.

E

to their deadly trap.

ven as they might inspire nightmares of glowing teeth in the

But there is more to life in the deep sea than feeding. Depictions

ocean dark, anglerfish are beautifully adapted to their deep,

of deep-sea anglerfish almost always display the females. That’s

dark home.

not because we don’t know what the males look like, but because

Even though the humpback anglerfish, Melanocetus johnsonii,

they are practically parasites that live off the female’s body.

might be the best-known anglerfish, it’s hardly the only one. Anglerfish belong to a group of fish called lophiiformes, and

Just like finding food in the deep sea can be a challenge, so

fossil evidence indicates that they’ve been around for at least

is finding a mate. Anglerfish don’t school, and so meetings

130 million years – about as long as birds with beaks. Different

between two anglers of the same species is a relatively rare

anglerfish species live at various depths – the red-lipped batfish

occurrence. To get around this problem, some anglerfish – like

is found in the shallows off Costa Rica and the striated frogfish

those in a group called the ceratiidae – evolved a different way

is primarily found in the Photic Zone around equatorial coasts –

of mating. Instead of resembling each other, the males and

but the most striking of all are those who spend their entire lives

females are wildly different. The females are the anglerfish that

in darkness. Of the more than 200 anglerfish species known, most

match our visual impressions, relatively large and toothy, while

of them live deep.

the males are much smaller in comparison. The only objective in the male’s life is to find a female to attach to – otherwise,

Naturally, anglerfish get their name from the characteristic lure

he perishes.

jutting out from above their mouths. The lure is really a modified fin ray with a decorative, luminescent end. Specialized bacteria live within this organ, which gives the lure an ability to glow and catch the attention of unwary prey. Anglerfish can even twitch

Opposite Not only do anglerfish have large jaws, but their stomachs can expand to hold prey twice as large as the anglerfish itself.

and wiggle their lures, adding just that little bit more enticement

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ANGLERFISH

133

The relationship between males and females in these anglerfish

While some big-mouthed fish – like gulper eels – use their

has required some substantial anatomical modifications. Males

mouths like nets to catch large quantities of small prey, anglerfish

often have a strong sense of smell and specialized eyes to help

often seek out larger morsels. These fish not only possess large

them locate a female. Many cannot eat – their jaws and even their

jaws full of prominent teeth, but their bellies can expand to

throats are effectively vestigial, making it impossible for them

accommodate prey twice as large as the anglerfish itself. Such a

to feed. But if a male finds a female, he attempts to bite her and

meal can nourish an anglerfish for a long time, a way to make the

attach himself. If successful, the immune system of the female

most of whatever they might find in deep water. These fish don’t

anglerfish doesn’t even realize that it’s being attacked. The male

chase their prey, but instead try to bring the prey close enough to

stays latched, releasing an enzyme that erodes the female’s skin

strike – a much more energy-efficient strategy when food is hard

and tissue to allow the male to fuse to her body. Sometimes, in

to come by. And if an anglerfish finds a good fishing spot, they

fact, multiple males may fuse to a single female at once, tapping

might stay there. At least one deep-sea anglerfish has been seen

into her blood vessels to gain their life support. The males then do

hanging upside down in the water column, with its lure hovering

nothing more than hitch a free ride and are immediately available

above the burrows of small creatures. These fish not only have

when the female is ready to spawn.

lures, but sometimes they go fishing themselves.

Not all anglerfish reproduce this way. Some species have

Above From the shallows to the deep sea, anglerfish are defined by their specialized lures that help entice prey closer to their jaws.

females and males that are able to catch their own food and spawn more like other bony fish. But the symbiotic method used by some

Opposite Some anglerfish species show extreme sexual dimorphism, with females being large, free-swimming predators and males living a parasitic lifestyle on the larger females. Here, two males hitch a ride.

species speaks to the challenges of living deep, when the basics of life cannot be taken for granted.

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2,000 metres

Hydrothermal Vents The geologists had a hunch. In 1976, working from previously discovered undersea activity, researchers aboard the R/V Melville outfitted a deepsea, remote-operated vehicle to detect temperatures at depth near the Galapagos Islands. The scientists suspected that there might be hydrothermal vents – points on the seabed where molten rock came close to the surface and created extreme temperatures – but no one had ever documented such a phenomenon before.

A

deep-sea tow would help gather preliminary evidence, and so the remote-operated “fish” went down to take readings

and snap photographs. At first, the gathered data seemed inconclusive. The expedition geologists found a slight rise in ocean temperature, but not an extreme one. There seemed to be many large clams in the area of the rise, as well, but the experts weren’t sure that the clams were alive or that the location was their natural habitat. The clams could have come from another source – the experts labelled the site “Clambake” after a far-fetched idea that a party ship had dropped shucked clam shells overboard. But these early glimmers would result in a discovery the following year that fundamentally changed our understanding of our planet and its life. In February 1977, marine scientists returned to the possible hotspot and lowered another rig capable of taking more photos –

Right Hydrothermal vent from James Cameron’s documentary Aliens of the Deep, 2005. Opposite “Black smoker” chimneys caused by iron sulphides at a hydrothermal vent.

136

HYDROTHERMAL VENTS

137

138

HYDROTHERMAL VENTS

over 3,000 during the course of 12 hours. Many were of seemingly

the minerals precipitate out and sometimes lead to the formation

lifeless seafloor made up of relatively fresh lava. But 13 depicted

of chimney-like structures given names like “white smokers”.

an area absolutely covered in mussels, an abundance no one ever

But the most startling aspect of hydrothermal vents couldn’t

expected to see so deep down. Some of the photos also showed a

immediately be detected. The higher water temperatures around

strange shimmer, a possible distortion caused by high heat.

the vents were not the only reason researchers found far more

A trio of researchers quickly decided to visit the site for

life than they were expecting. As experts began to study vent

themselves in Deep Submergence Vehicle (DSV) Alvin. Nothing

organisms – like the wonderful Riftia tube worms – they realized

could have prepared them for what they saw. There were cracks in

that these organisms had evolved an entirely different food web,

the lava field where super-hot water spewed out, turning cloudy

one which is based upon bacteria that are able to feed on the

as minerals in the heated water began to precipitate back out and

chemical compounds spewed out by the vents. The mineral-rich

fall to the seafloor. The crew found clams, crabs and octopus in

water provides ample food for bacteria, particularly compounds

the area, and subsequent dives uncovered additional sites with

rich in sulphur, and organisms like the tube worms are colonized

other forms of life – including a place they named the “Garden

by these bacteria. Many vent organisms don’t need to hunt or eat

of Eden” that was positively covered in huge tube worms with

food in the same way other deep-sea creatures do because they

bright red plumes (see pages 144–147). The experts had not only

are fed by the byproducts of the chemical-hungry bacteria inside

discovered hydrothermal vents, but that many forms of deep-sea

them, a process called chemosynthesis. This process is how life

life had adapted to make the most of these undersea hot spots.

can thrive in a world that never sees sunlight.

Marine scientists had unknowingly stumbled upon traces of

Hydrothermal vents are so new to science that we are only just

such vents before. Research in 1949 and 1960 found extremely

beginning to understand their implications. Life on Earth isn’t

hot and salty depths in the Red Sea. The records were treated as

wholly dependent on the sun, but instead can evolve alternative

anomalies until after the vents were rediscovered in the 1970s –

ways of feeding and surviving. The fact that evidence of

with many more to follow. To date, researchers have identified

hydrothermal vents have been found on Saturn’s moon Enceladus

over 200 hydrothermal vent fields in oceans around the world.

and Jupiter’s moon Europa, for example, has raised the possibility

There are certainly hundreds more that have yet to be recorded.

that chemosynthetic life exists elsewhere. And that may return

No two hydrothermal vents are quite alike in all details, but

experts to the origin of life on Earth itself. Perhaps life did not

their basic formation is the same. The vents are most often

begin in the sunlit shallows, but deep in the ocean dark. The only

found along mid-ocean ridges where magma comes close to the

way to know is to keep going back down.

seafloor. Cracks and fissures in the seafloor allow water to come in contact with rocks beneath the surface that have been heated

Opposite above Mussels and shrimp at a hydrothermal vent.

by the magma, the heat causing the previously chilly seawater to

Opposite below Photograph from the NOAA Submarine Ring of Fire 2006 expedition, which explored submarine volcanoes in the Pacific, shows life around an active vent (top right).

soak up more minerals before the water is vented back out above the seafloor. As the water mixes with the cold surrounding water,

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2,200 metres

Yeti Crabs until recently, no one knew that yeti crabs existed. Among the latest deep-sea creatures to be recognized by science, these crustaceans were given the genus name Kiwa in 2006. But these invertebrates aren’t like the ghost or fiddler crabs you might see scuttling along the shore. Not only do these long-armed, bristly crabs live deep, but they are principally found among hydrothermal vents and methane-rich environments called “cold seeps”.

D

espite several species being identified and named so far,

the crab can then eat in between lucky meals of decomposing

marine scientists didn’t discover the first-known yeti crab

organic matter. One Kiwa puravida crab has even been observed

species until 2005. Researchers aboard the DSV Alvin were 2,200

moving its arms in a repetitive and cyclic motion. Experts suspect

metres (7,217 feet) below the surface off Easter Island when

this wafts mineral-laden waters towards the bacterial colonies on

experts aboard noticed the unusual crustaceans. The name

the crab’s arms, thus feeding them and providing future snacks

“yeti crab” immediately came to mind because of the decapod’s

for the invertebrates.

long, almost hairy-looking arms, and analysis of collected crabs

Some yeti crab species look relatively similar to each other, like

confirmed that the invertebrate represented a new species,

spinier versions of the squat lobsters found elsewhere in the deep

genus and even family. This first crab was named Kiwa hirsuta,

sea. But others seem to stand apart, suggesting that there may be

and it didn’t have to wait long to gain company. Just a year later,

even more yeti crab forms waiting to be found. In 2015, marine

researchers on a dive off Costa Rica found what would eventually

biologists named Kiwa tyleri, which they nicknamed the “Hoff

be named Kiwa puravida, with several more added to the group

crab” because the setae on the underside of this species reminded

since those first finds.

them of actor David Hasselhoff’s hairy chest during his time

Like many crabs, Kiwa are scavengers. They use their short and

on Baywatch. This particular crab was found over 2,394 metres

powerful claws to snip off parts of whatever carrion falls to the

(7,854 feet) down in the southern Atlantic, the only yeti crab yet

bottom. But that’s not all. The arms of yeti crabs are covered in

found outside the Pacific Ocean.

setae – bristly projections that give the crustaceans their common

The fact that the “Hoff crab” has its bacteria-cultivating setae

name. Bacteria that can break down sulphur compounds have

on its underside rather than its arms has puzzled biologists,

been found on the setae of Yeti crabs, suggesting that the spines

which may indicate a difference in feeding strategy that’s

are not for protection but instead act as gardens for bacteria that

evolved over vast spans of time. Genetic studies of yeti crabs

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YETI CRABS

hint that they have been evolving apart from each other for

rocks around the hydrothermal vents. Often, little could be

millions of years. That makes sense given that hydrothermal

seen of them beyond the tips of their arms. Once the experts

vents open and cool over time, being temporary spots on the

knew what to look for, however, they began to notice the crabs

seafloor, and they are widely dispersed. The eggs and larvae of

foraging for open mussel shells and holding their hairy arms over

yeti crabs travel far and require enough good fortune to settle

warm water. Those distinctive arms are important for another

near a vent ecosystem in order to survive – almost like islands

reason. Yeti crabs don’t have eyes and cannot see, meaning that

underwater. Different vent systems have different particulars, or

the setae on their bodies have to detect the chemical signals and

at least act as somewhat isolated evolutionary pockets, and so

changes in pressure that allow crabs to navigate and forage in

even organisms of the same family can evolve distinct ways of

their undersea habitats. The crabs live in a way that is entirely

tackling the same biological requirements.

alien compared to what we’re familiar with on the surface, and yet they have been down there, surviving in the lightless depths

The way these crabs live may have helped conceal their presence

of the ocean.

even as marine scientists became increasingly enchanted with hydrothermal vents. The crabs are relatively large, about 15 centimetres (6 inches) long, but the first expedition to find

Below The fluffy projections along the arms of yeti crabs give these crustaceans their name.

them noted that yeti crabs often hide behind or underneath

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2,600 metres

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Methanogenic Bacteria No organism is an island. Even a self-contained cell, like a foram in its spiky shell, relies on other organisms for food. Many organisms rely on symbiosis – when two different species share space or even the same body, usually to the advantage of both – such as the sponges a giant spider crab sticks to its shell or the E. coli in the gut of a whale.

M

icroorganisms, especially, often live within the bodies

In 2020, marine scientists announced that they had found a

of animals and can do everything from helping digest

way in which some tube worms can use methane-eating bacteria

food to creating bioluminescent lures. Researchers are still

to feed themselves. In deep water off the coasts of California

discovering such interactions in the deep ocean, including among

and Costa Rica, researchers found methane-eating bacteria in

microorganisms known as methanotrophs that survive on

the plumes of the tube worms Laminatubus and Bispira. In fact,

methane.

what drew the attention of biologists to these two species in

Microorganisms that rely on methane are key to a great deal

particular is that their plumes seemed a bit fluffier and puffed

of the deep sea’s biodiversity. In addition to the hydrothermal

out than other species. Marine scientists have begun taking this

vents, marine geologists have also found deep-sea methane seeps

characteristic as a sign that deep-sea organisms are increasing

– fissures in the seafloor where the gas bubbles up from deeper,

the surface area of their bodies – much like the setae on the

carbon-rich rocks. They are important sites in the Earth’s carbon

arms of yeti crabs (see pages 140–141) – to cultivate colonies of

cycle, where microorganisms feed on carbon in rocks below the

chemosynthetic bacteria.

seafloor and release methane in the process. That methane, in

Methanotrophs aren’t only found in the deep sea. Wherever

turn, becomes food for other bacteria that then can become a

you can smell a natural methane source – such as from a salt

food source for animals or become incorporated into the bodies

marsh – there are methanotrophs present. But those that live in

of sea creatures. And much like Riftia (see pages 144–147) and

the dark parts of the oceans have garnered special attention for

other animals around hydrothermal vents, small tube worms of

two reasons. The first is that methanotrophs that live on and in

the methane seeps have found a way to make the most of bacteria

other organisms provide food to species that might otherwise

that can convert natural compounds into food.

not be able to exist in such hostile habitats. Just like the bacteria

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METHANOGENIC BACTERIA

around hydrothermal vents, they are an essential part of deep

sea surface

habitats that rely on chemosynthesis. But the second is far more important to us. the air, methane is more than 25 times as effective at trapping heat in our atmosphere than carbon dioxide. If all the methane

200

from the bottom of the sea were to bubble up and be released, the effects could be swift and disastrous. Thankfully for us,

~350 m (~1,150 ft)

100

Methane is a potent greenhouse gas. When released into

300

methanotrophs and the creatures they live inside alter methane and prevent the gas from reaching the surface, instead keeping it within ocean habitats. Researchers have estimated that these

methane plume

seafloor

400

bacteria might trap and transform about 90 per cent of the methane seeping from the seafloor, an essential ecosystem

500

service for all life on Earth. The relationship between methanotrophs and the organisms they live within goes back a very long way. Even though fossils of deep-sea organisms are rare, palaeontologists have nevertheless

and the bacteria – an ancient case of symbiosis that has helped to

found evidence of tube worms like Laminatubus and Bispira around

protect the terrestrial world from excess greenhouse gases since

prehistoric methane seeps preserved in Jurassic rock. Their

the time Stegosaurus walked the Earth.

presence there was not understood until the discovery of the methane-dependent worms at the bottom of our modern oceans. The mere presence of the ancient worms in the seep environment

Top Small tube worms are among the deep-sea creatures that rely on methane-hungry bacteria.

hints at a similar, if not the same, relationship between the worms

Above Sonar image of a methane plume in the Atlantic Ocean.

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2,600 metres

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Giant Tube Worms In film and fiction, we often wonder what it would be like to meet an alien species – an organism whose biology is so fundamentally different from our own that we would be nothing less than astonished. While life elsewhere in the universe has yet to be discovered, researchers have nevertheless found earthly species that have caused them to reconsider what they thought they knew about biology on our planet. One of these creatures is Riftia pachyptila – giant tube worm of the deep sea.

R

iftia are immediately recognizable. Aside from being

At first, the abundance of the worms around the undersea

enormous, reaching lengths of over 3 metres (9 feet 10 inches),

hydrothermal vents was a mystery. The deep sea is very cold, about

these cousins of the average beachside sandworm have a ghostly

4°C (39°F), but the water around the vents was incredibly hot,

white outer tube from which their blood-red plumes extend. They

over 350°C (662°F). These worms weren’t just hanging on, they

often live in great colonies, dozens and dozens of tubes growing

were thriving – along with crabs, clams and other invertebrates

next to and atop one another, over 2,600 metres (8,530 feet) below

found among the nests of Riftia.

the surface. The worms are responsive, able to retract their red

Dissections of the worms only revealed them to be stranger

plumes into their bodies if bothered like other tube worms do, but

still. Riftia, it turns out, do not have a digestive system. How

the fact that they make permanent homes near undersea vents was

could these worms survive without one? The answer, biologists

a clue to just how unusual these invertebrates are.

eventually discerned, is chemosynthesis.

No one had seen anything quite like Riftia until 1977. In that

Thanks to the outpouring of the thermal vents (see pages

year, the crew of the DSV Alvin (see pages 168–173) was studying

136–139), the water in these deep-sea habitats is loaded with

deep-sea hydrothermal vents off the Galapagos Islands when they

carbon, sulphur, nitrogen and oxygen. These create an abundance

spotted vast colonies of the worms around the openings in the

of carbon dioxide, sulphide, and other molecules that the worm

ocean floor. The expedition was led by geologists – not biologists – but they took enough samples for zoologists to get a better look

Opposite Enormous tube worms with bright red plumes were among the most striking early discoveries around hydrothermal vents.

at these unexpected annelids (or segmented worms).

144

GIANT TUBE WORMS

145

retains in its feathery, bright red plume and moves them to another part of its body called a trophosome – a vascular organ inside the worm that is absolutely brimming with bacteria. As the bacteria feed on the chemicals provided by the worm, they give off byproducts that the adult worm, in turn, feeds on. Strange as it might seem, Riftia do not spend their entire lives glued to the rocks around hydrothermal vents. In fact, that would be a terrible survival strategy. Hydrothermal vents open and close over time, often with the movements of the tectonic plates that make up the Earth’s crust. If a hydrothermal vent is pushed away from the underlying hot spot that created it, then the organisms that rely on the heat and outflow of the vent would entirely perish. Fortunately for Riftia, they start life as swimming larvae. The entire lifespan of Riftia is a remarkable example of co-evolution, not just between the worm and its life-giving bacteria but between the worm and its environment. A larval Riftia doesn’t look like much more than a small blob with little hairs called cilia to push it around. These larvae swim through the ocean depths, roving distances over 100 kilometres (62 miles) if necessary, and many never find a suitable home. But a lucky larva may settle near a hydrothermal vent and glom itself on to the sea bottom nearby, ready to change into a large, redplumed adult. Microorganisms around the vent are crucial for the transformation. When a larval Riftia finds a suitable place to settle, the worm doesn’t have its essential bacteria. Riftia only get the bacteria they need from the surrounding environment. The bacteria colonize the inside of the worm and cause its anatomy to change in response, forming a trophosome that will provide the worm with the bacterial byproducts it needs for food. Within two years, the Riftia become adults and are sexually mature, creating vast mats tens of metres/feet wide of worms ready to reproduce. When the time is right, triggered by an as-yet-unknown cue, the male worms release sperm into the water that then enter the tubes of the females to fertilize their eggs. The swimming larvae soon leave to find new homes in the dark of the ocean, continuing the life cycle of this unusual annelid.

Right Riftia worms get their nutrition from specialized bacteria in their bodies that feed on chemical compounds in the water.

146

GIANT TUBE WORMS

147

2,600 metres

• i

Chimaeras When we think of fish with skeletons made of cartilage, sharks and rays are the most familiar. Many live along the coasts and near the surface, easy to spot in the water or washed up on the shore. But these famous, flexible fish aren’t the only swimmers of their kind. Sharks and rays have an entire group of deep-sea relatives. They’re variously known as spookfish and ratfish, among other names, but many of us know them as chimaeras.

148

CHIMAERAS

O

ne look at a chimaera and it’s easy to understand why

have three sets of tooth plates that help them crush and grind

they’re sometimes called “ghost sharks”. They share a lot in

food, similar to some rays and other bottom-feeding fish. In a

common with sharks – from their triangular dorsal fins to their

sense, chimaeras are a bit of a mix of a shark body shape with the

streamlined shape – but the resemblance begins to fade from

feeding preferences of a ray.

there. Modern chimaeras are almost universally small, the largest

These strange fish have been swimming around the seas of

of known species being about 1.5 metres (5 feet) long. Chimaera

our planet for a very long time. Even though the earliest fossil

species often have large eyes and blunted snouts that make some of

chimaera is around 330 million years old, biologists suspect that

them look much more adorable than their toothy shark relatives.

they evolved even earlier – around 420 million years ago. They

Then again, male chimaeras have a special, grasping sexual organ

didn’t start off as deep-water fish. Many chimaeras lived in the

called a tentaculum on their heads.

shallows, and some were incredibly strange. Helicoprion was a

Marine biologists have been fortunate enough to observe

cousin of the modern ratfish that could grow to the size of a large

how the tentaculum works. Odd as it may seem to have a sexual

shark and had a circular-saw-like whorl in its lower jaw that it

organ on the head, far from the claspers of the male or vent of

used to shuck ancient cephalopods out of their shells. It was only

the female, the placement of this structure works for these fish.

over time, as chimaeras went extinct in the upper ocean waters,

During courtship, males use their tentaculum to press down and

that they became dedicated denizens of the deep. Surviving in deep water often relies upon making the most

hold on to the pectoral fin of the female, locking the two fish

of whatever happens to drift by, fall to the bottom, or live in

together for the duration of their encounter. There are a few other features that help distinguish chimaeras

Opposite The enigmatic whorl-tooth fish Helicoprion was an ancient relative of modern ratfish.

from sharks. While most sharks have five gills – with a few exceptions having six or seven – chimaeras tend to have four. And

Above Chimaeras are sometimes called “ghost sharks” for their spooky appearance.

instead of rows and rows of teeth that pierce or stab, chimaeras

149

the sand. Chimaeras use electroreception – a skill shared with

so, there are some chimaeras that marine biologists have been

sharks (see goblin shark, pages 88–91) – to pinpoint small prey

able to discern a little more about. In the waters of the Pacific

such as worms, octopus and crustaceans, sucking them into their

Northwest of North America, divers sometimes encountered

mouths and crushing the titbits with plate-like teeth. Chimaeras

spotted ratfish, Hydrolagus colliei. These chimaeras grow to about

won’t turn down carrion, either, and sometimes remote operated

97 centimetres (3 feet 2 inches) long, with males being smaller

vehicles encounter their haunting silhouettes around whalefalls

than females. They’re immediately recognizable by a dappling

and other sources of deep-sea carrion. Some chimaeras even have

of white spots against the red of their body. And though many

specialized anatomy to help them better find and snaffle up tiny

ratfish move themselves about by flapping their pectoral fins, the

prey from the sea bottom. The Australian ghostshark lives off the

spotted ratfish takes it a bit further, with underwater acrobatics

coast of Australia and New Zealand, and uses a shovel-shaped,

that have been compared to barrel rolls. Even in the darkness of

trunk-like extension of its nose to probe through the muddy

the sea, some fish show off.

bottom for food. Dozens of chimaeras have been named by researchers, but many

Below The elephantfish is a species of chimaera that uses its peculiar snout to search for invertebrates in the sand.

remain poorly known. Studying the anatomy of specimens taken from the deep or that wash up on shore is one thing, but trying

Opposite Male chimaeras have a small grasping organ called a tentaculum on their foreheads that helps them hold on during mating.

to investigate the behaviour of the living animals is another. Even

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CHIMAERAS

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2,500 metres

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Blubber Where would whales be without blubber? The fatty tissue is insulation, fat storage, a buoyancy assistant, an energyrich source of food for predators, and more, all hidden behind the body walls of many creatures whose ancestors transitioned from life on land to life in the seas.

A

mong modern animals, you can find blubber beneath the

resemblance isn’t just in the bones. In 2018, palaeontologists

skin of whales, seals and sea lions, penguins, and manatees.

announced that the Jurassic, 180-million-year-old ichthyosaur,

That’s astonishing. None of these creatures are close relatives

Stenopterygius had blubber. The fossil, found in a quarry in

of each other – penguins and manatees last shared a common

Holzmaden, Germany, preserves portions of the marine

ancestor more than 312 million years ago – and yet they have

reptile’s skin. Palaeontologists have recently confirmed that

all evolved the same solution to the challenges of living at sea. In

such fossils often retain traces of their original biomolecules,

fact, not only has blubber evolved multiple times among different

and, in this case, the ancient skin retained some of the hallmark

seagoing vertebrates, but it’s far older than anyone expected.

biochemical indicators of blubber. The fatty tissue likely helped

Fish-like reptiles called ichthyosaurs proliferated through the world’s oceans between 236 and 96 million years ago. Some of

These pages Many different organisms have independently evolved blubber, including whales, penguins, seals and sea lions, and even ichthyosaurs.

them, like Ophthalmosaurus, have often been cited as examples of convergent evolution with dolphins (see pages 62–65). But the

152

the ichthyosaur maintain a warm body temperature – estimated

with these insulating coats is that they trap air, which can then

to be about 35°C (95°F) – especially if the reptile ventured below

be squeezed out with increasing depth. Blubber, being squishy

the sunny surface waters.

and internal, can compress with pressure, and as an added bonus,

Instead of evolving just once, blubber has originated time

the blood vessels around the blubber can squeeze shut to keep all

and again among groups of land-dwelling vertebrates whose

the warm blood circulating at the animal’s core. Blubber is part

descendants made a home in the seas. In most cases, the lipid-rich

of what allows cetaceans like Cuvier’s beaked whales (see pages

tissue covers almost the entirety of an animal’s body, except the

156–159) to make their astonishing dives into the Twilight Zone.

limbs, and is connected to the underlying structure of the body

Blubber also helps whales and other creatures to save energy.

with tendons and ligaments. And some animals really pack it on.

Part of the reason why a dolphin – or an ichthyosaur, for that

Depending on time of year and age, for example, blubber might

matter – seems so streamlined is because the blubber beneath

make up fully half of a whale’s body mass.

their skin helps to give them a smoothed, sleek form that water

Understanding what blubber does helps to explain why this very

can more easily pass over. On top of that, fat is a buoyant tissue. It

useful tissue has evolved time and again. For one thing, marine

can help animals with large blubber stores stay near the surface to

mammals and other creatures wrapped in blubber – like penguins

feed, for example, or reduce the amount of energy required for a

– often rely on the fat’s ability to store energy for their survival.

deep-diving animal to return to the surface.

Mother elephant seals, for example, often build up as much blubber

This is not to say that all creatures with blubber use it in the exact

as they can before the pupping season. They have to protect and

same way. Pinnipeds – seals, sea lions and walruses – usually have

feed their offspring while on shore for 8–10 weeks, unable to return

both fur and blubber, which take on different roles. Fur seals have a

to the sea to eat without risking the survival of their babies. Instead,

greater density of hairs on their pelts than many of their relatives, for

the mother elephant seals subsist by burning off their blubber, a

example, and so their fur insulates them and their blubber mostly acts

source of energy, but also of hydration, as metabolizing the fats also

as energy storage. Most other pinnipeds, by contrast, tend to have

releases enough water to prevent the seals from drying out.

more blubber and rely on the fats for both insulation and energy.

And for diving deep down, where temperatures plummet and water pressure increases with every metre/foot of depth, there

Below For walruses, blubber also acts as energy storage.

could hardly be a better adaptation than blubber. While some

Opposite Even in warmer waters, blubber can assist with buoyancy underwater.

diving animals keep warm with fur or feathers, the problem

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3,000 metres

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Cuvier’s Beaked Whale How long can you hold your breath underwater? For most people, the answer is somewhere between 30 seconds and 2 minutes. With a lot of training and some assistance from breathing pure oxygen, some people have been able to stretch that meagre amount of time to 24 minutes. But that’s still nothing compared to Cuvier’s beaked whale, known to scientists as Ziphius cavirostris. These snouty, medium-sized whales can stay below for 3 hours and 42 minutes, long enough to slide into the oceans’ midnight Zone around 3,000 metres (9,842 feet) below the surface.

E

ven though Cuvier’s beaked whales aren’t nearly as famous as the great baleen whales or playful dolphins, they are

still a common and widespread whale species. These whales are found in all but the coldest of ocean waters worldwide and don’t look quite like most other familiar cetaceans. They have almost porpoise-like faces on long, tapering bodies topped with a small dorsal fin near the base of the tail that gives them something of a long cigar shape. Even though Cuvier’s beaked whales are still swimming through the seas today, the first scientist to describe them thought they were extinct. In 1823, the French anatomist Georges Cuvier wrote about an unusual whale skull found on the Mediterranean coast that didn’t match any recognized species. Given that Cuvier believed that much of the world had already been well explored and most large animals had been documented, he assumed that the skull must be from a long-extinct cetacean species and gave the whale its scientific name. It wasn’t until 1850 that another anatomist found a skull from the same species on a beach and realized that Cuvier’s beaked whale was still very much alive.

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CUVIER’S BEAKED WHALE

Opposite Cuvier’s beaked whales are named after the French anatomist Georges Cuvier. Top Skull of a Cuvier’s beaked whale. While they are technically “toothed whales”, they only have vestigial teeth along the jaw. Above Cuvier’s beaked whales often feed on squid. One individual had more than 200 squid in its stomach when it died.

157

Among whales, Cuvier’s beaked whale is what’s called an

squid from the Twilight Zone. The whales will eat fish, shrimp,

odontocete – a toothed whale like dolphins, porpoises and orcas.

crustaceans, and other food, but squid are clearly a favourite. One

But the name is a little misleading in this case. Both males and

particular whale from the California coast was found with 200

females of Cuvier’s beaked whale have a set of small teeth that

squid in its stomach, food likely found by echolocation as the

are thought to be vestigial, slowly evolving away, while the males

whale navigated in the dark. Precisely what allows Cuvier’s beaked whales to break diving

have a set of tusks on their lower jaws. Rather than impaling fish and other small prey on their teeth

records isn’t fully understood. The whales can dive much faster than

like some other toothed whales do, Cuvier’s beaked whale feeds

scientists can, even in specialized equipment, and are notoriously

in an entirely different way. As the whale approaches a morsel –

hard to observe as they descend. One hypothesis is that the whales

let’s say a small squid – the mammal opens its jaws and sucks its

are able to collapse their rib cages and lungs to cope with the

tongue back to create a small vortex that draws the prey into the

intense pressure as they hold their breath. Another possibility is

whale’s mouth. This is called suction feeding, and it’s a strategy

that the whales have a slow metabolism which allows them to ease

that Cuvier’s beaked whales use way down in the dark parts of the

the build-up of lactic acid as oxygen is used up on a dive. Food isn’t the only reason that these impressive cetaceans go

ocean, where light entirely fades out. So far, Cuvier’s beaked whale holds the record for the deepest-

deep, however. The longest dive for a Cuvier’s beaked whale yet

diving mammal. The record-setting dive was recorded off the

recorded is about 222 minutes, an incredible feat. But the whale

California coast in 2014 when a whale being tracked by scientists

was probably not seeking out food. Less than a month before

dived to about 3,000 metres (9,842 feet). That’s over 700 metres

the record dive, the individual whale had suffered exposure to

(2,296 feet) deeper than sperm whales. But that’s not the only way

intense sonar signals from the US Navy. The whale might have

that researchers know that these whales reach incredible depths

been diving deep to avoid the noise again, a reminder that what

for an air-breathing mammal. They also look at the stomach

we do near the surface can have profound consequences.

contents of stranded whales. What Cuvier’s beaked whales eat varies from place to place. The whales off the California coast feed on different prey than those

Below Stranded Cuvier’s beaked whale, La Jolla, California, 1959.

in the Mediterranean, and, naturally, a deep-diving whale will

Opposite Cuvier’s beaked whales are the deepest diving mammals on the planet, reaching over 3,000 metres (9,842 feet) below the surface on a single breath of air.

have to choose among what it finds on any particular deep-water foray. In general, though, Cuvier’s beaked whales appear to prefer

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CUVIER’S BEAKED WHALE

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3,500 metres

• i

Paleodictyon The deep sea is full of mysteries. There are species researchers know little about, creatures that have yet to be glimpsed, and longstanding enigmas that continue to evade attempts to solve them. Among these puzzles is a creature – if it even is a creature – which researchers call Paleodictyon nodosum.

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PALEODICTYON

I

n 1850, the Italian naturalist Giuseppe Giovanni Antonio

would belong to the ranks of many other fossil oddities that are

Meneghini described an odd, honeycomb-like fossil. The

difficult to understand from across such a broad span of time. But

polygons in the rock were what palaeontologists would later

Paleodictyon traces are not just found in Cambrian rocks. They

identify as trace fossils – indentations in sediment that record

have a fossil record that stretches across hundreds of millions of

the behaviour of prehistoric life, such as dinosaur tracks. These

years. The youngest Paleodictyon fossils are about 50 million years

are different from body fossils, which record the form of ancient

old, an incredible range for any organism. But that’s not all.

organisms themselves. But what might have seemed like just

For over a century, Paleodictyon was thought to be extinct.

another fossil curiosity has gradually turned into a persistent

The trace only appeared in the fossil record. But in 1978,

conundrum that continues to nag at experts hoping to classify

oceanographers Peter Rona and George Merrill published a

what Paleodictyon is and understand what sort of organism creates

report on Paleodictyon sighted on the modern sea bottom. These

the structure.

traces were not exposed fossils, but had been freshly made. Even now, in the deep sea, something is making the characteristic

Paleodictyon fossils are among the earliest known traces in the

honeycombed patterns of Paleodictyon.

fossil record, dating back 541 million years – and perhaps even more – into the Cambrian period. This was a time when animal life was in its infancy on Earth, a time when many of the earliest

Opposite Fossils of Paleodictyon show a distinctive, honeycomb pattern.

creatures looked strange and entirely unconventional to our

Above Map showing the Mid-Atlantic Ridge, where samples of Paleodictyon were taken in 2003.

modern eyes. And if Paleodictyon was just another odd fossil, it

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Palaeontologists have been striving for decades to understand what Paleodictyon represents. The entire fossil is made up of hexagon or hexagon-like divots separated by small ridges only 1–2 centimetres (up to ¾ inch) across. This makes up a kind of mesh that looks almost like scales on patches of the sea bottom. Some experts have proposed that these structures are burrows created by small, as-yet-unknown creatures. Then again, these structures might represent the pathways of foraging creatures, a way to trap food, or traces left by the growth of an unidentified species that lives in the sediment on the ocean bottom. At present, it seems that Paleodictyon probably does not represent a burrow or is in any way excavated from the sediment. It’s more likely that the fossil is either some kind of imprint created by a living thing – or that these structures are made by some nonliving geologic phenomenon that has yet to be recorded. The fact that Paleodictyon is still found in ocean habitats about 3,500 metres (11,482 feet) down makes the case all the more frustrating. This prehistoric enigma, which has been around for over half a billion years, is still here, yet no one has been able to observe how these structures are made. That’s not for lack of trying. During a 2003 expedition along the Mid-Atlantic Ridge to investigate hydrothermal vents, researchers aboard the DSV Alvin (see pages 168–172) found and took samples from Paleodictyon on the sea bottom. The hope was that the scientists might be able to capture the organism that creates the burrows, or some sort of evidence – be it body part or organic byproduct – that would offer a clue. But no sign was found of the trace’s creator. This led experts to propose that whatever is creating Paleodictyon made the mesh to trap bacteria the creature could later feed on, but this idea has yet to be verified. The slow pace life can take in the deep ocean might confound attempts to find and identify what Paleodictyon truly is. Perhaps, researchers speculate, the mesh represents the structure of a sponge or similar creature that has perished and been slowly eaten away by bacteria to only leave an outline behind. Organisms called xenophyophores – essentially armoured amoebas that are known to live in the deep (see pages 164–167) – are also candidates. Despite appearing fresh, there’s really no telling how old any given Paleodictyon “burrow” is. With how little the deep seabed gets disturbed, such traces might last for centuries. It’s like chasing a ghost. Right The oldest Paleodictyon fossils are about 541 million years old, but no one yet knows what these traces really represent.

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PALEODICTYON

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4,000 metres

Foraminiferans Around 55 million years ago, the deep sea suffered an extinction event. At that time, which palaeontologists describe as the Palaeocene–Eocene Thermal Maximum, vast amounts of greenhouse gases were released by volcanoes and deep-sea methane pockets. The influx of these gases caused a sharp warming spike that dramatically altered life on Earth. On land, humid forests became drier, and mammals became smaller due to environmental disturbance.

B

ut the hot temperatures didn’t just affect life on land. The

While not all forams have them, the most distinctive part of

warmer climate was so intense that it altered the nature of

many forams is their shell – technically called a “test”. The test

ocean currents, causing warmer waters near the surface to be

can have one or several chambers and, depending on the species,

shunted deeper down. The effect shocked some of the creatures

can be made of different materials. But the test is not an external

that lived there, most of all a curious group called benthic

home, like a hermit crab’s shell. The test grows within the cell

foraminifera. These deep-dwelling microorganisms were like

membrane of the foram, enclosed within the animal’s body. It’s

amoebas inside shells made of calcium carbonate, and about 37

like an internal skeleton, with the chambers housing the nucleus,

per cent of their species disappeared from the deep in short order.

and organelles like mitochondria. The test also has holes that

The foraminiferans – or forams – did not disappear entirely. In

allow the pseudopods – or “false feet”, much like the extensions

fact, they are among the hardiest and most resilient of organisms

of an amoeba – to extend out into the water and move the foram

in the seas. The earliest forams evolved more than 650 million

along or gather food. Forams have different ways of obtaining

years ago, long before the first recognizable animals, and they can

nutrients from filter-feeding to penetrating the tests of other

still be found in habitats ranging from the surface to the deepest

forams, making this group of ancient organisms incredibly

oceans. Scientists have recognized over 4,000 living species, and

adaptable.

there are almost certainly many more.

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FORAMINIFERANS

This page Foraminiferans are amoeba-like organisms with a hard shell inside their bodies, and they are found from the surface of the seas to the deepest trenches.

165

166

FORAMINIFERANS

A few foram species, about 40, float as part of the oceans’

rapidly isn’t because of the land-lubbing dinosaurs, but because

plankton. Most, however, are tucked between grains of sediment on

the fossil record of forams show a sharp and abrupt response to

the sea bottom and pull themselves around with their thread-like

the impact’s aftermath.

appendages. They can be so numerous that sometimes the ocean

But that’s just one application of the deep history of forams.

sediment itself is primarily made up of their shells, the basis for the

Forams that live as plankton versus those that live on the sea

calcareous ooze that can eventually become vast accumulations of

bottom are often anatomically different and can be distinguished

chalk, like the famous Kansas chalk of the American Midwest that

from each other even in the fossil record. When geologists drill

often preserves the bones of ancient marine reptiles.

ocean cores, forams can act as proxies for the depth of a particular

Despite their small size and the fact that they almost never get

rock layer – with more benthic species indicating a deeper habitat

the spotlight, forams are an essential part of the deep ocean. A

– and even how salty the water was at a particular site. The fact

wide selection of oceanic organisms – from sand dollars to fish

that forams have existed for so long – and, with their shells

– eat forams. The small morsels are incredibly numerous, and

constantly falling to the sea bottom, have created what may be the

that abundance has assisted palaeontologists in their efforts to

best and most continuous fossil record of any group of organisms

study the deep past. Foram species are so distinctive and evolved

– means that the fleeting lives of today’s forams are tied to a

so quickly that some of them can be used as a kind of biological

history spanning hundreds of millions of years.

marker tied to particular time periods, and changes in which

Opposite Foraminiferans can move themselves around and capture prey by using arm-like projections called pseudopods.

species are present can document the speed of mass extinctions. Part of why we know the mass extinction that struck the Earth

Above After death, foraminiferans sink down through the water column and can accumulate into biogenic sediments on the sea bottom.

66 million years ago was caused by an asteroid and occurred

167

4,500 metres

• I

DSV Alvin The ocean is hostile to humans. We lack the fins, the gills, the blubber, and other adaptations that seagoing creatures rely on to navigate their world. The deep sea is inhospitable. Even with the help of scuba gear, there is only so far we can descend before the cold, the dark and the pressure prove to be too much. so glimpsing the deep sea has required inventions and vehicles that can withstand the extremes other organisms survive in, and few are as celebrated as deep submergence vehicle (DSV) Alvin.

T

o date, Alvin has made more than 5,000 dives and

During the time that Alvin was commissioned in the mid-

collected data from a range of undersea environments –

twentieth century, researchers who were curious about the deep

from hydrothermal vents to the Mid-Atlantic Ridge (see below)

sea were facing a problem. Undersea vehicles called bathyscaphes

– that have been incorporated into thousands of scientific

– such as the Trieste (see pages 208–211) – had allowed scientific

papers. Since the time of its first descent in 1965, Alvin has had

teams to reach incredible depths. But bathyscaphes were not very

an incredible undersea career.

manoeuvrable underwater. They could go up and down, but they

168

DSV ALVIN

Opposite Alvin on its first deep dive, 20 July 1965. Above Alvin on the deck of a support vessel. The mechanical arm folded on the front was used to gather specimens from the ocean floor.

169

170

DSV ALVIN

weren’t especially suited to having a look around or exploring

Alvin was given an update and a refit to be able to descend to

the initial area of the descent. Alvin, by contrast, was designed by

greater depths and was soon diving even deeper. This extended range allowed researchers to take the

General Mills’ electronics division to be able to wander and also

submersible to places humans had never seen. Scientists curious

collect specimens with the help of two robotic arms. Commissioned for use by the US Navy and the Woods Hole

about the Mid-Atlantic Ridge – where new rock pours out of the

Oceanographic Institution in Massachusetts, Alvin is crewed

ocean floor to spread the adjoining North America Plate from the

by a pilot and up to two scientists. Launched from the support

Eurasian and African Plates – used Alvin to dive there in 1974. It

ship R/V Atlantis, the submersible can descend to 4,500 metres

was Alvin’s crew who first discovered hydrothermal vents, and the

(14,763 feet) – just into the Abyssal Zone – during a nine-hour

strange lifeforms that live around them, in 1977. And Alvin was

dive. Alvin was also designed with a quick-escape option in case

the vehicle of choice to visit the wreck of the RMS Titanic in 1986.

the crew runs into trouble at depth. In the case of an emergency,

Yet it would be a mistake to say that Alvin is the same vessel

the titanium sphere containing the crew can be released to float

today as it was in 1967 or even 1986. Every three to five years,

to the surface while the outer shell of the vessel can fall away for

Alvin was completely taken apart so each piece could be inspected,

later retrieval.

replaced or updated. Even though the deep submergence vehicle

Soon after its construction and certification dive, Alvin was

retains the same name, every single part has been replaced or

put to work. In 1966, the US Navy deployed Alvin off southern

changed out at least once – a constantly shifting submersible

Spain to retrieve an unexploded hydrogen bomb that had been

that’s had its own evolution as technology and scientific needs

lost when the plane carrying it collided with its fuelling tanker.

have progressed. The last major update was in 2014 – which

Alvin located the bomb 910 metres (2,985 feet) below the surface

changed out the titanium sphere surrounding the crew while also

and brought it back up.

adding new cameras and lights – and Alvin was quickly put back into service to assess the damage of the 2010 Deepwater Horizon

But not all Alvin’s early forays into the deep went so smoothly.

oil spill in the Gulf of Mexico.

On 6 July 1967, the submersible was 610 metres (2,001 feet) below the surface when the it was attacked by a swordfish. The

Even all these years later, Alvin is still making dives. Who knows

fish’s irritation was so great that it accidentally became caught in

what the storied submersible will find on its next foray beneath

the Alvin’s outer shell and caused the crew to abandon the dive.

the surface?

They consoled themselves by cooking the swordfish for supper. Nor was that the last mishap. A little more than a year later, Alvin was being lowered into the water from its support ship when two

Opposite above Alvin exploring the deck of RMS Titanic, 1986.

cables snapped. The crew hatch was still open when this happened,

Opposite below In July 1967, a swordfish became caught on Alvin during a dive.

leaving the crew little time to escape before Alvin plummeted 1,500 metres (4,921 feet) to the bottom and couldn’t be recovered

Following pages Refitted and updated every few years, Alvin continues to ferry researchers into the deep.

until June of 1969. Despite the expensive and frustrating mishap,

171

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172

DSV ALVIN

173

6,000 metres

Abyssal Plain Discussions of the deep sea often focus on what lives in the void, the inky black space where strange creatures float and flash in the cold and dark. But all of that water overlays some fantastic geology and topography, entire landscapes of mountains and rises, valleys and trenches, created and altered by the motion of the Earth’s crust. among these features, some of the most important are abyssal plains.

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174

ABYSSAL PLAIN

I

f you were able to look at Earth without its oceans, to the ungarnished face of the planet’s geology, you’d find that most of

our planet is abyssal plain. Oceanographers estimate that abyssal

Opposite Abyssal plains rest in deep water off the continental shelf.

plains cover about half of our planet’s surface – more common than any terrestrial habitat we can name. Found at depths between 3,000 and 6,000 metres (9,842–19,685 feet), these broad,

Left Abyssal plains often form broad, relatively flat habitats between the continents and mid-ocean ridges.

flat spaces form most of the rocky basin that our oceans rest in. In simple terms, an abyssal plain is exactly what it sounds like. They are relatively flat expanses that are often found between continental rises – where the sea bottom gets ever shallower approaching shore – and mid-ocean ridges where new rock is formed and extruded where water meets stone. A lack of

our attention, many as-yet-unrecognized species in the oceans

strong bottom currents or other forces that might shape these

are single-celled microbes, worms that dig into the soil, isopods

environments mean that abyssal plains are some of the flattest

that crawl over the bottom, and more. The organisms that exist on the abyssal plain live in a very

and most uniform environments on the planet. The way abyssal plains form isn’t due to a single phenomenon,

different world than those species that float in the water their

but several different geological factors that come together to

whole lives. Species of the abyssal plains live at the sediment–

blanket the floor of the deep sea. Part of the story has to do with

water interface – where the water meets the underlying geology.

the mid-ocean ridges that often border abyssal plains. Mid-ocean

Here, creatures either live on top of the sediment or within it

ridges are places where magma from below the Earth’s crust rises

– behaviours like burrowing being much more common in

up to the surface. The outpouring of new rock drives out the

this habitat. While swimming species like sleeper sharks can

existing ocean crust, pushing it outwards from the ridge. These

be found gliding over the bottom, most abyssal plain creatures

same forces are part of why continents move, the plates they rest

are ones that we need to scan the surface or even dig beneath

upon almost constantly nudged by both the formation of new

it to even detect. Censuses of deep-sea life have estimated that

rock and older rock becoming subsumed.

previously unknown species make up about 80 per cent of all

But that’s not all. If the seafloor were only basaltic rock, it

those observed any time an exploration makes it down to the

would look quite different, textured by the cooled lava. Instead,

abyssal plain. Forget about coral reefs – if you’re hoping to find

much of the abyssal plain is smooth and made of fine-grained

new species in the sea, the best place to look is in the oceanic

sediment like silt and the shells of plankton that have drifted to the

muck covering the abyssal plain.

bottom. And in addition to the shells of diatoms, foraminiferans,

The incredible and largely unknown biodiversity of the abyssal

coccoliths and other plankton, geologic sediment comes from

plain is part of why these environments require protection. The

above, too. Sediment carried by rivers, wind and other sources

belief that the abyssal plain is essentially lifeless or unimportant

reaches the sea. From there, swift currents along the coast pick

to Earth’s ecology has led to any number of proposed uses, from

up the sediment and channel vast amounts of it down steeply

oil drilling to dumping hazardous waste. Such ventures can do

angled chutes called submarine canyons. These waters – rich in

irreparable harm to the deep sea. The International Seabed

sediments such as clay and silt – billow out and are distributed

Authority found that even a single deep-sea mining operation

over the sea bottom, covering up all the lumpy basalt.

could disrupt as much as 800 square kilometres (308 square

Abyssal plains are not oceanic deserts, as previous generations

miles) of seabed sediment each year and damage habitats more

of oceanographers supposed. Hydrothermal vents (see pages

than five times that size, given the way disturbed sediment would

136–139) and methane seeps are often found along the abyssal

fall back to the sea. In such a situation, we wouldn’t be aware of

plains, and these expansive habitats are also thought to contain

the impact on species there because they have likely not even

far more biodiversity than is presently known. Even though

been identified. Though it may look barren, the abyssal plain is

open-water swimmers like firefly squid and anglerfish often grab

practically writhing with life.

175

6,500 metres

• I

Sea Squirts Sea squirts are not the most charismatic of deep-sea dwellers. If you don’t know what you’re looking at, you might assume that they are translucent sacs just wafting to and fro. But these animals, technically called ascidians, are actually distant cousins of ours. They have what was the forerunner of a backbone – a notochord – that places these unassuming animals closer to us than to squid or any other undersea invertebrates.

176

SEA SQUIRTS

R

esearchers have named about 2,300 species of ascidians

tissue. None of the scientific crew had seen such a species before,

so far. Some live by themselves. Others form colonies or

but, on scouring the technical literature, they found that a team of

clusters, anchored to the sea bottom. Almost all are very small,

Japanese researchers had described something similar about two

between ½ centimetre to 10 centimetres (¼ inch to 4 inches) in

decades previously. The balloon was a form of sea squirt, albeit an

length, although free-swimming colonies of such animals can

undescribed species.

stretch about 18 metres (59 feet) – occasionally popping up on

Why the sea squirt might attach itself to the bottom with a tether,

social media as bizarre “mystery animals” that are actually moving

rather than adhering its whole body to the substrate like most of its

collectives of many small animals. As far as palaeontologists can

relatives, is still to be confirmed. Almost everything that’s known

discern, sea squirts and their relatives have been around since

about the creature comes from video footage. But, its discoverers

the Cambrian period, over 508 million years ago, and occur at a

speculate that the geological instability of the area might have

range of depths. It’s some of the deepest ones that we are only just

something to do with it. The Java Trench is a place where one tectonic

beginning to encounter.

plate of the Earth’s crust is being subsumed beneath another. That means a lot of earthquakes and lesser shake-ups. A sea squirt on the

In 2019, the crew of the Five Deeps Expedition was setting about its task of visiting the deepest spots in all five of Earth’s oceans when they encountered something fascinating at a depth of

Opposite Sea squirts can be found at all levels of the ocean, from the shallows to over 6,500 metres (21,325 feet) below.

about 6,500 metres (21,325 feet). In the lowest point in the Indian Ocean, within the Java Trench, the explorers saw what looked like

Above Many sea squirts live in colonies or clusters, which can make them look like one large animal.

a living balloon anchored on the bottom by a string-like thread of

177

sea bottom might get covered up or otherwise smooshed, whereas

on the bottom, they start their lives as larvae that swim in the

the tether allows this species to better survive the tumult.

water column. They look like small tadpoles, twitching their little

Whether at the bottom of the Java Trench or in the sunlit waters of

muscles to move their tails. And in these larvae, it’s easier to spot

the Photic Zone, sea squirts share some basic characteristics. Many

their notochord – a flexible rod of tissue that, in evolutionary

of these organisms are filter-feeders. Water passes through their

terms, was a precursor to the first spinal columns. Some of our

tubular oral siphon to the mouth and throat, where organic matter

most ancient relatives, such as Pikaia, found in the Cambrian

and plankton are consumed, before exiting the body. This simple

Burgess Shale, had notochords and bodies similar to this, which

feeding method has allowed sea squirts to survive in a variety of

means that sea squirt larvae are almost like a little time capsule

ocean environments, the simplicity of their biology giving them a

of where our own vertebrate family got its start. That’s why the

much broader range than more specialized forms of sea life.

strange balloons bobbing off the bottom of the sea are our distant cousins, relatives that took a different evolutionary route more

But some sea squirts have adapted this rather passive technique,

than half a billion years ago.

especially those that live deep down. An entire family of sea squirts, the octacnemidae, live between 500 and 8,000 metres (1,640–26,246 feet) below and have siphons modified into

Above Like Cambrian creatures such as Pikaia, sea squirts have notochords, or precursors of spinal cords that define vertebrates.

grasping lips. These modifications allow them to catch moving prey when it comes close, giving the sea squirts a little more of a

Opposite A 2019 expedition to the Java Trench found a new, unusual species of sea squirt attached to the bottom by a tether.

caloric boost than the strictly filter-feeding species. Our own connection to these squishy animals can best be seen

Following pages Many sea squirts are filter-feeders, but a few are carnivorous and are capable of engulfing moving prey.

when sea squirts are young. Before settling down to their spot

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SEA SQUIRTS

179

180

SEA SQUIRTS

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7,000 metres

I

•

Sea Spiders Let’s make something clear right at the outset – sea spiders are not actually spiders. Even though most have eight legs and look vaguely spider-like, these invertebrates belong to their own group called pycnogonida.

T

hey are ancient; their fossils dating back more than half a billion

more than 7,000 metres (22,965 feet) below. Most have four pairs

years. In fact, sea spiders might represent the closest relatives to

of legs, though a few have five or six. Most of the time they crawl

all other arthropods, a glimpse at what the ancestors of insects, true

over the sea bottom in search of worms, sponges, anemones and

spiders, crustaceans and other joint-legged invertebrates were like.

other prey that’s unlikely to swim away, although when sea spiders

And there are a lot of them. So far, marine biologists have named

themselves need to get away quickly they can swim by pushing their

more than 1,300 species of these oceanic crawlers.

legs in an undulating motion that makes them look like swimming

In one form or another, sea spiders can be found almost

umbrellas. For a time, researchers called them “no-body crabs”

everywhere. They live in every ocean, from the shallows to depths

because they seemed to simply be the legs of a crab without the body.

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Most sea spiders in the shallows are relatively small. The

therefore can become large enough to be conspicuous. Food

tiniest has legs that are only 1 millimetre long. But as you go

supply could be another factor, especially because sea spiders can

deeper – or into waters that are much colder, like those around

scavenge and therefore aren’t as restricted as deep-sea specialists.

Antarctica – sea spiders become far bigger. The largest yet found

It’s likely that there isn’t one single answer, but a combination of

has legs 70 centimetres (27½ inches) long, 700 times the size of

factors that have caused deep-dwelling spiders to live large.

the smallest. Another giant, found at depths between 2,200 and

Despite looking very spider-like, sea spiders don’t eat their

4,000 metres (7,217–13,123 feet), is even named Colossendeis for

meals like their terrestrial namesakes. Instead of jaws tipped

its impressive size.

in fangs, sea spiders have a proboscis that they insert into their

Precisely why sea spiders become larger at depth and in colder

prey like a mosquito before starting to suck out the fluids within.

temperatures is a mystery. Marine biologists call the phenomenon

During observations around a whalefall off the California coast,

“deep-sea gigantism”, although that’s more of a description of a

for example, researchers noticed sea spiders on cushy pom-pom

pattern than an explanation of it. There could be multiple reasons.

anemones that had aggregated near the decomposing whale.

Biologists know that the ability of creatures to shed or retain body

Sea spiders were often crouched over the anemones, sticking

heat varies with size. The bigger you are, the more internal volume

their proboscis into anemones’ arms one at a time to suck out

you have and the easier it is to hold on to heat. That’s maybe one reason why populations of creatures in colder habitats – whether

Opposite Sea spiders are only distantly related to terrestrial spiders.

it’s elk or sea spiders – might be larger. Then again, it’s possible

Above Preserved specimen of Colossendeis shows the proboscis used to suck fluids out of prey.

that sea spiders have fewer predators in ever-deeper water and

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SEA SPIDERS

the liquids within. The affected anemones didn’t look as healthy

spiders were likely crawling over the sea bottom at the same time

as those that hadn’t been latched on to, but they were still alive.

that Anomalocaris (see pages 52–55) was swimming through the

By sucking just enough fluids to survive without killing the

water above. While many Cambrian oddities and wonders went

anemones, the sea spiders may inadvertently be ensuring their

entirely extinct, there are some – sea spiders among them – that

food supply in days ahead. Rather than consuming the anemones,

have stood the test of time and still call the seas home. When you

they were harvesting what they needed from them.

look at a sea spider crawling along the sea floor, you’re getting a glimpse at hundreds of millions of years of life’s history.

Sea spiders have been living this way for a very long time. In 2002, palaeontologists described the delicately preserved larvae of a sea spider found in the Cambrian rock of Sweden. The placement of the mouth and anatomy of the larvae’s legs matched

Opposite The sea spider species that live in cold environments – such as off Antarctica or in the deep sea – tend to be large.

up with many modern sea spiders, although there were enough differences to know that this little fossil speck was something

Below Those in shallower water, such as this one in the Bali sea, tend to be small, even tiny.

more primitive. Still, creatures very much like modern sea

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Dumbo Octopus Of all the denizens of the deep sea, dumbo octopus might be the most adorable. Not a single species, but more than a dozen described since the late nineteenth century, these cephalopods became social media favourites thanks to their rounded bodies, small eyes and ear-like fins that give them more than a passing resemblance to the Disney character that gives them their common name. But there’s much more to these deep-down octopods than their cute appearance. These softbodied creatures have thrived in dark waters around the world.

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cientists first became acquainted with dumbo octopus in

observe them in the wild. So far as experts have been able to tell,

1884. In that year, French anatomist Paul Henri Fischer

dumbo octopus live in the chilly, abyssal parts of oceans around

named Grimpoteuthis umbellata from specimens collected from

the world and have a range of about 1,000 to 7,000 metres (3,280–

deep waters off the coasts of Morocco and the Azores. These

22,965 feet). The species that live at the outer boundary of this

were not like the octopus that slip between rocks and reefs in

range are some of the deepest cephalopods known.

shallow, light-filled waters. These octopus had eight arms and no

What marine biologists have been able to glean about these

tentacles, like all octopus, but the suckers along the underside of

charismatic little invertebrates is not what one might expect

those arms formed single rows, with little spines jutting to either

from the name “octopus”. Many familiar octopus species in the

side. The large fins and stubby body were unusual, too, which

Photic Zone zip around thanks to jet propulsion, blasting water

would eventually lead to the common name of these octopus

through a tube on the body that pushes the octopus backwards,

after the release of the movie Dumbo in 1941. Over time, scientists

with its arms trailing after. Dumbo octopus might be able to do

kept finding more of these odd octopods – and still are. In 2021,

this, but that doesn’t seem to be the main way they get around.

researchers named yet another species, Grimpoteuthis imperator

Grimpoteuthis species move through the deep sea by flapping their

from the North Pacific.

large fins and by using their sensitive arms to walk themselves along the sea floor. Instead of floating in the open water, these

Despite their internet fame, however, dumbo octopus aren’t very well known to researchers. It’s difficult to study animals that live in near-perpetual darkness thousands of metres/feet below

Opposite Dumbo octopus were originally described in 1884 but only got their popular name after the release of the Disney film Dumbo in 1941.

the surface, where researchers may only have a few moments to

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DUMBO OCTOPUS

187

Above All dumbo octopus belong to the genus Grimpoteuthis, but how the species differ from each other in their behaviour and biology is still poorly known. Opposite A dumbo octopus uses its large arms to move through the water. Following pages Photograph of the underside of a dumbo octopus’s arms shows the suckers in single rows.

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DUMBO OCTOPUS

cephalopods seem to be demersal – a term for organisms that live

centre of their arms where it can be nipped at or otherwise

on the seabottom.

consumed with a beak-like structure called a radula. Some

Jet propulsion isn’t the only octopod skill that Grimpoteuthis

Photic Zone species even latch on to clams and other hard-

seems to lack. Dumbo octopus also don’t produce ink. That might

shelled prey, using their radula to effectively drill through the

seem like a great disadvantage to a mostly soft, slow-moving

defences of their prey to the softer parts inside. But dumbo

invertebrate, but it makes sense when you consider where these

octopus take a simpler approach. It seems that at least some

cephalopods live. Ink might not be much of an effective defence

species, such as Grimpoteuthis boylei of the Northeast Atlantic

in a habitat that is mostly or entirely dark. Instead, these octopus

Ocean, hover just above the surface of the seafloor and pounce

use a trick common to cephalopods – colour camouflage.

upon unwary invertebrates such as small worms and isopods.

Grimpoteuthis species have specialized cells in their skin called

They eat their prey whole.

chromatophores, which produce colour. These cells can expand

There’s a great deal marine biologists still don’t know about

or contract to help make different shades and patterns, and

dumbo octopus. No one is sure how long dumbo octopus live,

experts hypothesize that the ability to shift between shades of

or even the specifics of how they reproduce. Some species

pink, white, red and brown might help these octopus blend

photographed or filmed also seem to roll their arms up in unusual

into their surroundings and avoid detection – not to mention

ways. Experts do not know whether this is for communication or

communicate with other Grimpoteuthis.

something else entirely. Every time a dumbo octopus is spotted

The way Grimpoteuthis species feed is also better suited to

by a submersible or remote operated vehicle (ROV), there’s the

the deep than to the shallows. Octopus higher up in the water

potential to learn something new about these common but rarely

column grab prey with their arms and stuff it towards the

seen creatures.

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Giant Isopods If you’ve ever flipped over a log in your yard or a forest, you may have seen little, grey critters with segmented shells crawling around beneath it. These, depending on where you live, might be called pill bugs, roly-polys, woodlice, or other names, and they are all land-dwelling forms of a group of crustaceans called isopods – more closely related to a crab than to a grasshopper. Now imagine such a creature as large as a football and you’ll have some idea of the isopods that live in the deep sea.

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o far, marine biologists have named about 20 different species

Giant isopods are primarily scavengers. When a shark, a whale,

of giant isopods that live in the deep-water environments

a fish, or the carcass of some other creature sinks and settles on

of the Indian, Pacific and Atlantic Oceans. All belong to the

the bottom, giant isopods seek out the free meal and begin their

same genus, Bathynomus, and vary in size and other particulars

deconstruction project. Modified legs help bring food to the four

depending on their environment. There are probably even more,

sets of jaws these crustaceans use to break up their meals. But

as yet undiscovered by researchers. But the largest and most

that’s not to say that giant isopods will refuse something fresher if

famous of all is Bathynomus giganteus, an invertebrate that can

it comes along. They will slurp up worms, nibble at sea cucumbers,

grow to about 35 centimetres (13¾ inches) long. And much like

and chew up sponges if they happen across them. Fish are their

their garden-variety relatives, these giants can roll into a ball to

most favoured food. When a dead whale sinks to the bottom,

defend themselves against predators.

giant isopods of one species or another are often among the first ones at the dining table during the mobile scavenger phase (see

Despite being world-famous for its size, the largest of the giant

pages 114–117).

isopods lives in one particular part of the deep ocean. Bathynomus giganteus is found in environments ranging from 1,000 to 7,000

That these creatures – and many others – live in the deep ocean

metres (3,280–22,965 feet) deep in the Gulf of Mexico and other

is still a relatively new idea so far as the history of science goes.

parts of the Western Atlantic. These are invertebrates that are

Giant isopods were not described by scientists until 1879. Up until

well adapted to the cold and dark and are rarely seen in warm

the 1860s, much of the deep ocean was thought to be virtually

or shallow waters. Instead, they form a persistent and important

empty of life below 550 metres (1,804 feet). But this could only be

part of the deep-sea’s clean-up crew, as they patrol the muddy

based on the idea that what ships brought up in deep-sea trawls

ocean bottom.

could be taken at face value and recorded an accurate picture of

192

GIANT ISOPODS

Above Why deep-sea isopods are larger is a mystery, part of a phenomenon marine biologists know as “deep-sea gigantism”.

193

Above The eyes of giant isopods are not only large, but also have over 4,000 individual facets each. Opposite above X-ray of a giant isopod, Bathynomus giganteus. Opposite below Giant isopods are sometimes harvested for food in Taiwan, where they are served boiled with rice.

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GIANT ISOPODS

life in deep water. By the 1860s naturalists were beginning to find and describe life below the 500-metre (1,640 feet) cutoff, and the discovery of giant isopods was a significant confirmation that there were indeed large organisms and other mysteries that had yet to be uncovered. What has puzzled biologists, however, is why isopods seem to be so much larger in the deep sea than those in the shallows. This is contrary to what many naturalists expected, given that deep waters are cold, dark, and not nearly as rich in food as those closer to the surface. Even though a single explanation for the size of these crustaceans hasn’t been agreed on, scientists nevertheless have a few theories. One possibility is that the lower temperatures of deep-ocean zones cause the individual size of Bathynomus cells to be larger, therefore leading to larger body size. Another possibility is that the cold waters slow down the metabolism of the isopods such that they live for much longer and, less constrained by time, can keep increasing in size for as long as they live. Being big can also help isopods withstand undersea famines. A bigger isopod will have more fat reserves, allowing the invertebrates to gorge in times of plenty and withstand periods when juicy carcasses might be harder to find on the bottom. The answer might involve some of these possibilities, or none of them.

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8,183 metres

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HMS Challenger In the entire history of deep-sea exploration, there’s one name that bobs to the surface again and again: HMS Challenger. Even though naturalists had been fascinated with the ocean and its deepest reaches for centuries prior to the ship’s 1872–76 expedition, it’s the voyage of the Challenger that is often cited as the birth of oceanography. The ship’s name is even immortalized on maps of the seas – the most distant part of the Mariana Trench, which

Challenger discovered, is called the Challenger Deep.

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HMS CHALLENGER

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hallenger didn’t start as a scientific vessel. Built in

the British Government, HMS Challenger – stripped of guns and

Woolwich Dockyard and launched early in 1858,

refitted to make space for scientific study – was the vessel of choice.

HMS Challenger was a Royal Navy corvette that could use

The crew would include six scientists among its full complement

steam power when necessary. Her early history was one

of 200. The ship was ready to sail on 7 December 1872.

of colonialism; the warship was used in the occupation of

While other expeditions – such as that of the famous HMS

Mexico’s port at Veracruz and shelling of a village in Fiji. The

Beagle that took a young Charles Darwin to the Galapagos – were

change in the ship’s story, which would eventually overshadow

imperial expeditions that carried naturalists on board, the voyage

the vessel’s wartime activities, would come at the prompting of

of Challenger was specifically scientific. Initially headed towards

English marine scientist Charles Wyville Thomson.

the Canary Islands in the eastern Atlantic, the ship covered over

In 1870, Thomson approached the Royal Society of London

127,600 kilometres (79,286 miles) and logged 362 stops during

with an idea for a grand expedition. Most of what people knew

its world cruise. These breaks from the open sea were necessary

about the seas came from the shoreline or occasional observations by ships at sea. Many saw the oceans as incredibly sparse, almost

Opposite HMS Challenger was launched in 1858 as a war vessel and later refitted as a scientific ship.

like aquatic deserts. Yet no one had really studied the seas in detail. Thomson wanted to conduct such studies, across oceans

Above Group of officers on the deck of HMS Challenger during the scientific expedition.

over a multi-year voyage. And when his request was approved by

197

(not just for refitting). Thomson and the other scientists aboard wanted to keep regular intervals, taking depth soundings and making collections on a rhythm so that the researchers could track sea changes across the latitudes and longitudes. Whatever the naturalists brought aboard, they studied in the ship’s lab , which was equipped with microscopes, specimen jars, hooks to hang larger animals, a library and all sorts of preservative equipment to make sure as much as possible made it back to England. The amount of oceanic information the crew collected is almost incalculable. No one had examined the seas like this before. But the observation that would make Challenger world-famous was a stop the ship made three years into its journey. In 1875, Challenger was cutting its way around the southern Pacific when the crew ran into a problem. The plan was to land at Guam, but intense winds prevented the ship’s landfall. So they kept going. Adjusting the route, Challenger stopped at the 225th sample collecting spot on 23 March, at a place between Guam and Palau. There, the crew dropped a weighted rope to the bottom – and it kept going. The depth sounding was recorded as 4,475 fathoms, or 8,183 metres (26,847 feet). No one had contemplated that the ocean could be so deep. Challenger did more than just detect the bottom of the world’s deepest trench. The crew also dredged what they could from the depths. Among the finds were fossilized teeth from one of the largest sharks that ever lived, Otodus megalodon, although the scientists aboard were just as excited about the ooze from the bottom of the sea. One of the sailors aboard wrote: “The mud! Ye gods, imagine a cart full of whitish mud, filled with minutest shells, poured all wet and sticky and slimy on to some clean planks.” While such practices might have been anathema to seasoned sailors hoping to keep the ship clean, such samples were scientific wonderments that no one had ever seen before. Challenger showed how little we knew about our own planet, beginning an enduring fascination with what lies far below.

Right The Challenger expedition made one of the first dedicated collections of deep-sea samples: from left to right, morid cod, juvenile female anglerfish, and sediment from the ocean floor. Following pages Track chart of the Challenger expedition, which covered vast distances and yet still only visited a small portion of the world’s oceans.

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9,000 metres

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Crinoids Animals don’t always look like what we expect. squid, fish, crustaceans and many other deep-sea species are immediately recognizable as animals, but not so with crinoids. These very ancient organisms are often anchored to the bottom, with feathery projections radiating out from the end of a long stalk. They, too, are animals, and they are some of evolution’s greatest survivors.

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rinoids are so inconspicuous that sometimes it’s easy to forget that they can still be found in modern seas. The fossil

record is absolutely full of varied crinoid species that thrived for hundreds of millions of years, persisting even as more charismatic animals like trilobites and ammonites entirely disappeared. Along with brachiopods, crinoids are the unsung stalwarts of the deep sea – almost all the way to the darkest and most distant depths. In the vast tree of life, crinoids are echinoderms – relatives of starfish and sand dollars. Mature crinoids have a mouth at the centre of their feather-like arms that sift plankton and other organic matter from the water. Once snagged, those tiny pieces of food are passed along the arms by hair-like cilia arranged along the appendages. The crinoid body is primarily centred around a cup-like arrangement of plates that hold the animal’s vital organs. Most crinoids become anchored to the bottom, although there are some that swim freely in the water column or can even crawl along the sea bottom using their arms to drag themselves along. And while they might seem like part of the oceans’ backdrop, they have maintained a diverse array of species despite some major setbacks during Earth’s Big Five mass extinctions. Scientists have recognized about 600 crinoid

202

CRINOIDS

Opposite Crinoids can look like undersea feather dusters, but are, in fact, animals related to sea stars. Above Crinoids are often anchored to the sea bottom by a stalk which ends in a crown of arms surrounding the mouth and body.

203

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CRINOIDS

species – not too bad for animals that originated before any

Japanese researchers spotted stalked crinoids over 9,000 metres

plants or animals lived on land.

down in the Izu-Ogasawara Trench, off the island nation’s

Tracing the origins of crinoids is a challenging task. It’s possible

eastern coast. The crinoids were small, with arms only about 10

that the first crinoids date back to the time of the Burgess Shale

centimetres (4 inches) across, anchored to hard, rocky parts of

and animals like Anomalocaris, over 508 million years ago. A strange

the sea bottom. Experts did not recognize the species, made more

fossil called Echmatocrinus might be the earliest crinoid, although it

challenging by the fact that they could not collect the specimen,

could also be a form of coral. The earliest definitive crinoids, then,

but the find left no doubt that crinoids have been able to make

date to rocks about 480 million years old from a time called the

their home in the deep with just as much ease as the upper levels

Ordovician. And from that point, crinoids underwent an impressive

of the ocean.

evolutionary explosion. Dozens and dozens of species evolved to

While many organisms in the deepest zone of the oceans seem

filter food from the water, and as crinoid predators evolved – such

relatively rare or specifically adapted to the harsh conditions, the

as the earliest fish – these sea lilies and feather stars began evolving

crinoids caught on video by the Japanese scientists didn’t seem all

in new species. Some crawled and swam rather than staying in

that different from others. The researchers noted that the deep

one place. Others became incredibly spiny and almost club-like

crinoids were abundant and showed the same feeding postures as

in appearance. And despite almost going extinct during a terrible

others. While it’s possible that there’s an unknown hydrothermal

mass extinction 252 million years ago, some crinoids persisted

vent nearby, the researchers found no evidence of such a deep-sea

and began to proliferate anew during the Age of Dinosaurs and

oasis. Instead, it’s more likely that the Izu-Ogasawara Trench is a

beyond. Perhaps they might not be as charismatic as a giant squid

kind of natural trap for organic matter from higher ocean levels –

or anglerfish, but crinoids certainly have staying power.

enough to let crinoids hold tight at extreme depth.

Crinoids can be found at almost any depth, from near the surface to approximately 9,000 metres (29,527 feet) down. This is

Opposite Illustration of crinoids from the Devonian period, which floated upside down in the water column.

a relatively recent find. Even though oceanographers have trawled up evidence of deep-sea crinoids before from depths below 6,000 metres (19,685 feet), it’s only been recently that researchers have

Above Crinoids were more numerous and diverse in the past, with today’s species representing only a fraction of what once existed.

been able to visit those at the deepest depths. In 2009, a team of

Following pages Crinoids attached to wreckage off the Solomon Islands.

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10,911 metres

Trieste It’s one thing to know that the ocean is incredibly deep. It’s another to visit those places. Ever since the discovery of the Challenger Deep, oceanographers have wondered about what might be down at such incredible depth. In 1960, a small crew would get the first direct look at this distant place in the submersible Trieste.

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TRIESTE

Snorkel

Water Ballast Tank

Gasoline Tanks

Pellet Ballast Hopper

Ballast Release Magnet

Release Magnets

Vent Propellers

Entrance Tunnel

Vent

Pressure Release Valve

Release Magnets

Gasoline Tanks

•••

Pellet Ballast Hopper Floodlamps

Electronic Flash

Hatch

Water Ballast Tank

Ballast Release Magnet Window

Guide Rope

D

Observation Gondola

esigned by Swiss engineers and built in Italy, Trieste was

well as in the case of electrical problems. The ship’s buoyancy was

something of a halfway point between the bathysphere used

regulated by gasoline. That might seem like a strange choice, but it

by William Beebe and Otis Barton (see pages 80–83) and more

came down to physics. Gasoline is less dense than water and does

modern deep-sea vehicles like the ever-updated Alvin (see pages

not compress as easily under great pressure, assuring an ascent

168–173). Despite being over 18 metres (59 feet) in length, most

if the Trieste ran into trouble at depth. The engineers behind the

of Trieste’s bulk was made up of chambers to hold gasoline and

design did not want to take chances. Even the sphere attached

regulate pressure. Crew space wasn’t much more spacious than

to the bottom of the Trieste was designed to be 12.7 centimetres

Beebe and Barton had in their bathyscaphe. The Trieste had a

(5 inches) thick and able to withstand greater pressures than were

crew of two, held within an observation gondola suspended

expected. No one had been down so deep before, and estimating

below the vessel. The explorers would enter from the top of

the conditions the crew might find was more difficult than

Trieste, going through the midsection of the vessel to reach the

planning a launch outside the atmosphere.

hatch into their windowed bubble. But the Trieste was designed to

Originally operated by the French Navy, the Trieste was sold to

do something entirely different from the comparatively shallow

the United States Navy in 1958. The American military had big

dives of preceding submersibles. There were no air hoses or

plans for the submersible. Under Project Nekton, the US Navy

cables connected to the Trieste. The vessel was designed to make a

planned several deep dives in the Pacific with the goal of taking

free dive to the bottom, sinking and rising on its own.

measurements related to its performance – from effects of water

The Trieste used a combination of technologies to move up and

pressure on the hull and how far light reaches to where life in

down through the water column. Naturally, how to gracefully

the sea might be found. Following a few updates to the original

sink down to extreme depth and return was a huge consideration. To go down, crews loaded the Trieste with 9 metric tonnes (19,841

Opposite Don Walsh and Jacques Piccard aboard Trieste in 1960.

pounds) of iron pellets in interior silos. These were held in by

Above General arrangement of Trieste. The bathyscaphe was operated by the French Navy before being purchased by the US Navy in 1958.

powerful magnets, allowing the ballast to be released at depth as

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design, the Trieste was carried out to the waters off Guam in 1959

reach the surface while the crew inside shivered in the 7°C (47°F)

with the ultimate goal of exploring the Challenger Deep.

cold and ate chocolate bars. They only spent 20 minutes on the

Following surveys that used depth charges, rather than

bottom before their ascent, but that was long enough to know

weighted rope, to find the bottom, the crew of the Trieste started

that even the deepest parts of the ocean supported life. Over a

their deep dive on 23 January 1960. Aboard was Jacques Piccard –

mucky ocean bottom made of decomposing diatoms, Piccard and

son of Auguste Piccard, who designed the Trieste – and Don Walsh

Walsh saw flounder swimming. Even though humans, wrapped

of the US Navy. Dropping at nearly 1 metre (3 feet) per second,

in tons of technology, could just barely visit the Challenger Deep,

the descent to the bottom took 4 hours and 48 minutes. It was a

life had found a way to adapt to one of the harshest environments

harrowing trip. At about 9,000 metres (29,527 feet), one of the

on the planet.

outer Plexiglass window panes of the observation bubble cracked.

Above Final checks are made to the Trieste before its record dive to the Mariana Trench.

But Piccard and Walsh continued. Eventually they reached a depth of 10,911 metres (35,797 feet). It was so far beneath the surface

Opposite The crew was confined to the observation gondola suspended below the main vessel.

than it took about 7 seconds for voice messages from the Trieste to

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TRIESTE

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10,984 metres

Mariana Trench The Mariana Trench is Earth’s deepest place. In the whole of the world’s oceans, even among the Abyssal Zone habitats where organisms must eke out a living in the perpetual aquatic dark, there is no place that compares.

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he Mariana Trench is not a single, even point along the ocean

call the Challenger Deep. The incredible pressure in these depths

bottom. Instead, this grand crevice stretches about 2,500

reaches over 1,000 times the pressure at sea level, equivalent to

kilometres (1,553 miles) in a crescent-shaped slice in the western

about 50 jumbo jets piled on top of one another. Only a few people,

part of the Pacific Ocean. The deepest part of the trench – the

in specially designed craft, have ever made brief visits here.

portion that has transfixed human imaginations for decades – is

The Mariana Trench is geologically complex and was created

10,984 metres (36,036 feet) below the surface, a dark place experts

by the motion of Earth’s crust. The process works like this: the

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MARIANA TRENCH

rocky outer shell of our planet is made up of about seven massive

that dense, heavy body of rock is slowly being shoved beneath

plates, and these plates move. As magma from within the Earth

the comparatively lighter Mariana Plate to the west. What the

oozes out of ocean ridges and creates new crust, the older and

Mariana Trench really is, then, is the deepest part of the boundary

heavier parts of the crust begin to sink and get pushed beneath

between these two great geologic provinces.

other plates. Additional forces can be at play – like heat from the

But the fact that this great subduction zone remains so deep has

Earth’s mantle – but the manner in which new crust is formed

to do with another quirk of location. Rivers and other moving

and is subsumed is thought to be the primary way these plates

bodies of water on a continent often drain to the sea, carrying

get pushed around. All this moving and shaking helps to create

tons upon tons of sediment with them. Divots on the ocean

Earth’s geological profile, including the Mariana Trench.

floor can become filled in over time if they’re close enough to a coastline. But while many of these trenches and subduction zones

Rather than being a standalone landmark, the Mariana Trench is part of an ocean subduction zone. This is a place where heavier,

Opposite Map of the Mariana Trench, showing the location of Challenger Deep.

thicker, older rock is pushed below a plate. The Pacific Plate that underlies much of the Pacific Ocean is relatively old, with

Below Parts of the Trieste were overbuilt to make sure the vessel could withstand pressures that no submersible had ever experienced before.

rock that formed during the middle of the Jurassic period, and

213

214

MARIANA TRENCH

are close to continents, the Mariana Trench is far from land and therefore has not been infilled over time. Scientists and naturalists have been fascinated with the Mariana Trench since HMS Challenger took the first sounding of the depths in 1875 as part of the ship’s three-year oceanographic survey (see pages 196–201). Even then, no one fully understood just how far down the trench went – the initial reading was 8,183 metres (26,847 feet). Later expeditions that used a variety of techniques – from echo soundings and sonar to rare visits with submersibles – found even greater depths. Despite the legendary status of the Mariana Trench as a realm of darkness and monstrous creatures in fiction, life has actually been very difficult to find in the deepest part of the oceans. In 2017, for example, researchers were thrilled to spot a pale snailfish at a depth of 8,178 metres (26,830 feet) in the trench. (Some previous fish sightings, such as a flounder supposedly seen in 1960, have been questioned or revised over time.) In 2014, another crew found a strange form of life – shrimp-like crustaceans called amphipods that grew far larger than their counterparts in the upper levels of the ocean. While many amphipods are about 2 to 3 centimetres (¾–1¼ inches) long, these “supergiants” reached up to 10 times that length. The amphipods are not the only giants in the depths. At 10,641 metres (34,911 feet) down, a 2011 expedition into the trench spotted immense, strange creatures that may be the largest individual cells on the planet. Technically called xenophyophores, these organisms are like soft-bodied amoebas with a hardened outer shell. While so common in the oceans that they are often little studied, some of the xenophyophores in the Mariana Trench were over 10 centimetres (4 inches) across – exceptionally large for a single-celled organism. Why these strange creatures live at such great depths is still unknown. But finding bigger versions of familiar organisms isn’t an unexpected phenomenon. Zoologists know this as deep-sea gigantism, where organisms like crustaceans, squid and eels tend to be larger with increasing depth. (See also sea spiders, pages 182–185 and giant isopods, pages 192–195.) Even though life in the deepest part of the seas is strange and relatively rare, it has undoubtedly found a way.

Left Computer model of the topography around the Mariana Trench (indicated by the purple arc) using data from ship soundings and satellite altimetry.

215

Glossary ..... . . . . . . . . . . . . . . . . ......... . . . . . . . . . . . . . . . . . . . . . ..... . . . . . . . . . . . . . . . . . . . . . . . ..... . . . . . . . . . . . . . . . . . . . . . . ......... . . . . . . . . . . . . . . . . . . . . . . ..... . . . . . . . . . . . . . . . . . . . . . . . ..... . . . .

ALGAE Photosynthetic organisms belonging to several different lineages,

independently evolve similar shapes, behaviours, or genetics, such

ranging from single cells to kelp.

as the comparable streamlined shapes of sharks and ichthyosaurs.

BATHYSCAPHE

COUNTERSHADING

A free-diving vessel that can move under its own propulsion for

A coloration pattern that is darker above and lighter below and

deep-sea exploration.

acts as camouflage.

BIOGENIC OOZE

CRETACEOUS PERIOD

Sediment made up of decomposing microorganisms and

The timespan between 145 and 66 million years ago, or the third

other organic matter, often plankton such as diatoms and

period in the Mesozoic era, after the Triassic and Jurassic.

foraminiferans.

CRUSTACEAN

CAMBRIAN PERIOD

A diverse group of arthropods that include crabs, shrimp, krill,

The time period extending from 541 to 485.5 million years before

isopods, copepods and others.

the present day, a time during which early animal life proliferated.

DEPTH SOUNDING

CEPHALOPOD

Measuring the depth of a body of water, which can be done by

A group of invertebrate animals, such as squid, octopus, cuttlefish

mechanical means with a weighted tether or technologies such

and nautilus, that have bilateral body symmetry and a head ending

as sonar.

in arms or tentacles.

DIEL VERTICAL MIGRATION CETACEAN

The daily movement of sea organisms, especially plankton and

Fully aquatic mammals, including toothed and baleen whales,

the fish that feed on them, up towards the surface at night and to

descended from land-dwelling ancestors.

lower depths during the day.

CHEMOSYNTHESIS

DREDGE

A biological process that converts molecules containing carbon

An apparatus that brings samples up from depth, such as sediment

into a source of energy.

or undersea organisms.

CONTINENTAL SHELF

ELECTRORECEPTION

The portion of a continent submerged beneath the ocean,

The natural ability to detect weak electrical fields, as in the jelly-

usually shallower than the continental slope that leads to the

filled pores of sharks.

Abyssal Plain.

FILTER-FEEDING CONVERGENT EVOLUTION

The behaviour of straining small organisms or organic matter from

When two different species or broader categories of organisms

the water column by means of baleen, gills or some other apparatus.

216

GLOSSARY

FOSSIL

ROV

A trace of ancient life more than 10,000 years old, including body

Remote operated vehicle, or an undersea exploration vehicle

fossils such as bones and trace fossils such as burrows.

operated by crew in another vessel.

HYDROTHERMAL VENT

SARCOPTERYGIAN

A fissure or opening in the seafloor from which heated, mineral-

A group of bony fish with lobe-shaped fins, including the living

rich water rises.

coelacanth species.

ICHTHYOSAUR

SCLERAL RING

Marine reptiles that evolved shark-like body shapes and lived

A circular arrangement of thin, plate-like bones in the eyes of

between 250 and 90 million years ago.

some vertebrates, such as fish and marine reptiles.

JURASSIC PERIOD

SONAR

The timespan between 201 and 145 million years ago, or the

Sound navigation and ranging, or a technique that uses sound to

second period of the Mesozoic era, between the Triassic and

communicate, detect and find objects or navigate.

Cretaceous.

STROMATOLITE MIDWATER

Dome-shaped geologic structure created by a mat of photosynthetic

The part of the oceans between the surface and the bottom, where

cyanobacteria adhering sediments together beneath it.

organisms live suspended in the water.

SUBMERSIBLE MOLLUSC

Any vehicle capable of movement underwater, including remote

A phylum of invertebrates including clams, snails and squid, all

operated vehicles and submarines.

of which have an organ called a mantle used for breathing and

TENTACLE

excretion.

A grasping appendage that’s flexible and elongated. In squid, there

NOTOCHORD

is one pair of tentacles in addition to eight arms.

A flexible rod in the bodies of some animals made up of a cartilage-

TEST

like material.

A shell, often used to describe the silica-based shells of diatoms in

PALAEOZOIC ERA

comparison to shells made of calcium carbonate.

The timespan between 541 and 251 million years ago, preceding

TRENCH

the Mesozoic era.

Long, narrow canyons, valleys or depressions in the seafloor

PHOTOPHORE

reaching kilometres below the general surface of the sea bottom.

A gland-like organ on an organism that produces light.

TRIASSIC PERIOD PHOTOSYNTHESIS

The timespan between 251 and 201 million years ago, the first

The natural process by which plants and other organisms use

period of the Mesozoic era, before the Jurassic and Cretaceous.

sunlight to make food from carbon dioxide and water.

ZOOPLANKTON PHYTOPLANKTON

Tiny planktonic animals, ranging from diminutive crustaceans to

Ocean-going microorganisms capable of photosynthesis.

the larvae of larger animals.

217

Index

.....................................................................................................................................................................................................................................

Numbers in bold refer to main subjects, including photos; in italic to all other photos/captions.

A

The Abyss (Abyssopelagic/Abyssal Zone) 13, 15, 171, 174, 186, 212

B

bacteria 142–3, 217

Cambrian Explosion 52–7

baleen whale 20, 23, 122, 125, 156, 216

Cambrian period 52–7, 128, 161, 177,

Abyssal Plain 11, 16, 174–5, 216

Bali sea 185

Acanthephyra purpurea 26

Barton, Otis 16, 80–2, 80, 81, 209

Cameron, James 13, 136

Aegean Sea 50–1, 51

basin 13, 88

camouflage 26, 26, 59, 99, 107, 107, 112,

AFB-14, USNV 40

Bathynomus, see giant isopods

Age of Dinosaurs 62, 205

Bathypelagic Zone, see Midnight Zone

carbon cycle 8, 142

Age of Exploration 92

bathyscaphes 168, 209, 209, 216

carbon dioxide 8, 15, 143, 144, 217

Age of Reptiles 70, 117

Bathysphere 6, 16, 16, 17, 80–3, 209

Catalina Islands 114

Alecton 92, 92, 93

Beacon, HMS 50

cephalopods 26, 47, 50, 66–9, 70–3, 92–7,

algae 21, 37, 38, 112, 216

Beagle, HMS 197

Aliens of the Deep 136

Beebe, William 16, 80–2, 209

Alvin, DSV 6, 114, 139, 140, 144, 162,

big red jelly 7, 108–9

168–73, 209

178, 178, 185, 205, 216

122, 126, 189, 216

149, 186–91, 216 cetaceans 20–1, 114, 154, 156, 158, 216

biodiversity 14, 51, 142, 175

chalk 37, 38, 167

amiiform locomotion 100

biogenic ooze 36–9, 167, 198, 216

Challenger, HMS 6, 51, 66, 196–201,

ammonite 70, 202

bioluminescence 14, 26–31, 41, 65, 99,

amoebas 22, 37, 74, 162, 164, 165, 215

104–7, 104, 105, 107, 122, 132, 142

215 Challenger Deep 6, 11, 196, 208, 210,

amphipods 37, 38, 125, 215

Bispira, see tube worms

anemones 59, 182, 183–5

bivalves 50, 128, 131

Chauliodus, see viperfish

anglerfish 26–9, 28, 29, 110, 132–5, 175,

“black smoker” chimneys 136, 137

chemosynthesis 15, 74–7, 109, 139,

198, 199, 205

blubber 7, 63, 99, 114, 152–5, 168

212, 212, 213

142–3, 144, 216

annelids, see tube worms

Blue Planet 10, 11

chimaeras 148–51

“Anomalocaris” briggsi 52–5, 55, 56, 185, 205

brachiopods 128–31, 202

Chun, Carl 66, 66

Antarctica 23, 183, 185

buoyancy 73, 122, 152, 154, 154, 209

cigar shark, see cookie-cutter shark

Arabian Sea 7, 74

Burgess Shale 52, 52, 53, 54, 55, 178, 205

cilia 146, 202

C

Cladoselache 32

Architeuthis dux 92, 94 arthropods 52, 55, 92–5, 216 Atlantic Ocean 112, 140, 143, 189, 192, 197 Atlantis, R/V 171 azoic hypothesis 6, 50–1

Clambake 138

calcareous ooze 37, 38, 167 calcium carbonate 38, 164, 217

218

clams 128, 128, 138, 139, 144, 189, 217 climate change 19

INDEX

co-evolution 146 coccoliths 37, 38, 38

D

Echmatocrinus 205 electroreception 150, 216

Daphnia 6, 84

elephant seals 154

Darwin, Charles 197

Emu Bay Shale 52–5

cold seeps 140

Davis, James 88

Epipelagic Zone, see Sunlight Zone

Colossendeis, see sea spiders

DDT 23

Eurypharynx, see gulper eels

continental rises 13, 175

deep-sea gigantism 183, 193, 215 (see also

Everest, Mt 12, 13

coelacanths 6, 7, 35, 44–9, 73, 88, 112, 128, 217

continental shelf 8, 13, 14, 52, 104, 131, 175, 216 continental slopes 13, 73, 216 convergent evolution 63, 152, 216

expeditions:

creatures by name) deep-sea perch, see orange roughy

1872–76 6, 51, 66, 196–201, 215

deep submergence vehicle (DSV) 6, 114,

2006 139

139, 140, 144, 162, 168–73

cookie-cutter shark 6, 26, 98–9

Deepwater Horizon 171

copepods 8, 86–7, 87, 216

demersal, defined 127, 189

corals 26

depth sounding 198, 216 (see also sonar)

core drilling 167

Devonian period 205

counterillumination 112

Diaphus lanternfish 107

countershading 216

diatoms 37–8, 38, 39, 175, 210, 216, 217

Courtenay-Latimer, Marjorie 41, 44, 45

diel (diurnal) vertical migration 6, 84–7

cow sharks 32

dinosaur tracks 161

crabs 6, 7, 11, 87, 114, 139, 140–1, 142,

dinosaurs 47, 62, 88, 143, 161, 167, 205

144, 158–61, 164, 182, 192, 216 Cretaceous period 37, 38, 44, 117, 216, 217

DNA sequences 16 dolphins 62, 63, 98, 152, 154, 156–8 dredge 50–1, 80, 117, 198, 216

crinoids 202–7

duck-billed platypus 88

crustaceans 26, 36–7, 58, 73, 84, 87, 110,

Dumbo 186, 186

125, 140–1, 150, 158, 182, 192–5, 202, 215, 216, 217 cuttlefish 70, 73, 216 Cuvier, Georges 43, 156, 156, 157 Cuvier’s beaked whale 7, 154, 156–9 cyanobacteria 52, 74–7, 217

dumbo octopus 6, 186–91

E

2019 177

F

facultative ectoparasitism 99 faecal matter 20–1, 21 false feet, see pseudopods filter-feeding 40–3, 55, 125, 131, 164, 178, 178, 216 firefly squid 26, 26, 27, 175 Fischer, Paul Henri 186 Five Deeps Expedition (2019) 177 food webs 11, 14, 22, 139 foraminiferans (forams) 37–8, 37, 74, 142, 164–7, 175, 216 Forbes, Edward 6, 50–1, 51 fossil(s), defined/described 7, 217 fossil records 11, 35, 41, 44–7, 45, 68, 88, 112, 161, 167, 202

Earth’s crust 8, 146, 174, 175, 177, 212

Fowler, John 99

Easter Island 140

French Navy 92, 92, 93, 208–11, 209

219

frilled shark 6, 32–5

Hoplostethus, see orange roughy

frogfish 132

humpback anglerfish 20

fur seals 154

humpback whale 20, 21, 22

G

Gaimard, Joseph Paul 98 Galapagos Islands 7, 136, 144, 197 Garden of Eden 114 Garman, Samuel 32, 32 General Mills 171

hydrothermal vents 7, 136–9, 140–1, 142–3, 144–6, 162, 168, 171, 175, 205, 217

I

L

Laminatubus, see tube worms lanternfish 11, 26, 29, 30–1, 104–7, 112 Latimeria 45, 47 lava 139, 175 light emission, see bioluminescence

Ice Age 32

living coelacanth 35, 45, 47, 217

ichthyosaurs 7, 62–5, 117, 152–4, 152,

living fossils 32, 121 lobe-finned fish, see sarcopterygians

216, 217

ghost sharks, see chimaeras

illumination, see bioluminescence

lophophore 131

giant isopods 6, 192–5, 215

insecticides 23

luminescence, see bioluminescence

giant oarfish 41, 84, 87, 100–3

internet outages 90

giant spider crab 6, 58–61, 87, 142

invertebrates 15, 20, 38, 50–1, 55, 58,

giant squid 6, 7, 11, 14, 51, 92–7, 132, 205

70, 114, 125, 140–1, 144, 150, 176, 182–5,

giant tube worms 144–7

186–91, 192–5, 216, 217

gigantism 183, 193, 215 (see also creatures by name) goblin shark 6, 32, 88–91, 128, 150 gombessa, see coelacanths

iron 20, 21, 136 Isistius, see cookie-cutter shark isopods 6, 8, 175, 189, 192–5, 215, 216

Great Barrier Reef 12, 13

Izu-Ogasawara Trench 205

great toothy shark 14

J

great white shark 41, 44, 98 greenhouse gases 8, 143, 164 Grimpoteuthis, see dumbo octopus Gulf of Maine 23 Gulf of Mexico 94, 171, 192 gulper eels 112, 122–5, 132 gut content 94, 102, 103, 124

H

Hadal Zone, see The Trenches hagfish 114, 116, 117, 118–21 Hamelin Pool 77, 78–9 Hawaii islands 7, 40, 108, 212 Helicoprion 148, 149, 149 hexanchiformes 32 Hoff crab, see yeti crabs Holzmaden 152

M

magma 139, 175, 213 mako shark 41 mame, see coelacanths manatees 152 Mariana Trench 8, 12, 19, 196, 210, 212–15 marine snow 15, 21, 37 mass extinctions 117, 131, 167, 202, 205 Matsumoto, George 108

Java Trench 7, 177–8, 178, 179 jellyfish 7, 11, 14, 15, 29, 100, 102, 103, 108–9

Mediterranean Sea 112, 156, 158 megamouth shark 7, 40–3, 85–7, 107 Melanocetus, see humpback anglerfish Melville, R/V 136

Jones, Everet 98–9 Jordan, David Starr 88, 88, 89 Jurassic period 62–3, 143, 152, 213, 216, 217

Meneghini, Giuseppe 161 Merrill, George 161 Mesopelagic Zone, see Twilight Zone Mesozoic era 23, 62, 117, 216, 217

K

methane-eating bacteria 7, 142 methane pockets 164

Kaempfer, Engelbert 58, 59

methanogenic bacteria 142–3

Kangaroo Island 52

Mid-Atlantic Ridge 7, 33, 161, 162, 168,

Kermadec Trench 212

171

Kiwa, see yeti crabs

Midnight Zone 13, 174

krill 20–1, 21, 23, 216

midwater 29, 217

Kyoichi Mori 92

migration 6, 8, 12, 19, 20, 21, 33, 84–7, 104–7, 114, 216

220

INDEX

mitochondria 38

Octopoteuthis, see squid

pressure 18–19

Mitsukurina, see goblin shark

octopus, see octopods

Project Nekton 209

molluscs 50, 128–31, 138, 139, 139, 141,

Ogasawara archipelago 94

protozoa 37

oil spills 171

pseudopods 164, 166, 167

morid cod 198

Old Fourlegs (Smith) 47

muciferous canal 126–7

Ophthalmosaurus 62–5, 152

mucus 121, 126–7, 127

orange roughy 126–7

Q

muscles 99, 109, 122, 178

organelles 38

Quoy, Jean René Constant 98

mussels 128, 128, 138, 139, 139, 141

Osedax 114, 116, 117, 117

myctophids, see lanternfish

Otodus megalodon 198

N

otoliths 104

R

National Oceanic and Atmospheric Ad-

Pacific Ocean 7, 73, 98, 110, 110–12, 139,

217

National Marine Fisheries Service (US) 127 ministration (NOAA) (US), see NOAA

radiolarians 37

P

ratfish, see chimaeras red roughy, see orange roughy

140, 150, 186, 192, 198, 209, 212, 213

Red Sea 139 Regalecus, see giant oarfish remote operated vehicle (ROV) 14, 15, 15,

Natural History Museum (UK) 16

Pacific Plate 213

nautilus 70–3, 216

Pacific viperfish 110

naval activity 41, 101, 171, 197–201, 208–11

Palaeozoic era 131, 217

navigation 103, 104, 141, 158, 168, 217

pale snailfish 215

NBC Radio Network 82

Paleodictyon 6, 7, 160–3

neon lighting, see bioluminescence

pelican eel 122, 123–5

Riftia tube worms 7, 139, 142, 144–7

Neritic Zone 14, 174

penguins 152, 152, 154

Ring of Fire expedition (2006) 139

New York Zoological Park 80

phosphorus 20, 23

Rona, Peter 161

nitrogen 20–1, 144

Photic Zone 8, 9, 12, 13, 14, 83, 132, 178,

Royal Navy (RN) 197–201

no-body crabs, see sea spiders NOAA 16, 139 Nonsuch Island 82

photophores 26, 69, 99, 107, 107, 112, 112, 217

notochord 121, 176, 178, 178, 217

phytoplankton 11, 19, 21, 21, 217

nutrient cycling 19, 20–5, 104–7

Piccard, Auguste 210

O

Piccard, Jacques 208, 209, 210

ocean temperature, see temperature ocean zones 12–15 (see also zones by name) oceanic divisions 174–5 Oceanside Harbor Beach 100 octopods 6, 70, 73, 73, 186–91

research vehicle (R/V) 98, 136, 171

Royal Society of London 197

186–9

photosynthesis 11, 14, 15, 21, 74–7, 217

oarfish 84

reproduction techniques 59, 69, 70, 107, 127, 134, 134, 135, 146, 149, 189

North America Plate 171

O’ahu 40

68, 92, 136, 150, 189, 217

Pikaia 178, 178 pinnipeds 152, 152, 154, 154 plankton 8, 11, 14, 19–21, 19, 21, 22, 36–7, 41, 55, 59, 66, 69, 70, 84–7, 87, 100–3, 103, 107, 127, 131, 167, 175, 178, 202, 216, 217 planktonic shell-builders 37–8 Pleistocene era 32 plesiosaurs 117, 117

221

S

Saccopharynx, see gulper eels Sagami Bay 6, 32, 88 Sahel Alma 88 sand dollars 50, 167, 202 sandworms 121, 144 sarcopterygians 44, 47, 48–9, 217 Scapanorhynchus lewisii 88 scleral ring 63, 217 Scripps Institution of Oceanography 84 SCUBA 12, 80, 168 “Scymnus” brasiliensis, see cookie-cutter shark sea cucumbers 192

sea lions 152, 152, 154

sulphophilic stage 114, 115, 139

US Navy 41, 84, 101, 158, 171, 208–11, 209

sea spiders 182–5, 215

sulphur 144

sea squirts 7, 176–81

Sunlight Zone 13, 14, 21, 29, 41, 47, 65,

V

sea temperature, see temperature

80, 87, 126, 174

sea turtles 117

swim bladder 104, 122

seals 23, 152, 152, 154

swordfish 99, 170, 171, 171

setae 140–1, 142

T

sharks 6, 7, 32–5, 40–3, 85–7, 88–91, 107, 198 shrimp 26, 58, 100, 103, 110, 125, 138, 139, 158, 215, 216 Sirena Deep 212 skipjack tuna 98, 99 slimehead, see orange roughy Smith, James Brierley 44–7 snaggle-toothed fish 15 snailfish 215 snails 114, 217 Solomon Islands 205, 206–7 sonar 16, 84, 85, 104, 143, 158, 215, 216, 217 sound navigation/ranging 217 Southern Ocean 23 sperm whale 13, 20, 62, 92, 158 spermatophore 69 sponges 55, 59, 142, 162, 182, 192 spookfish, see chimaeras squid 6, 7, 11, 14, 20, 26, 26, 27, 29, 35, 36, 51, 55, 62, 66–9, 73, 73, 84, 90, 92–7, 100, 103, 110, 112, 125, 126, 128, 132, 157, 158, 175, 176, 202, 205, 215, 216, 217 starfish 50, 51, 202 Steenstrup, Japetus 6, 92

Temminck, Coenraad 58, 58, 59 temperature 15, 16–17, 19, 35, 47, 73, 87, 136–9, 154, 164, 183, 195 temporary habitats, see whalefalls tengu 88, 88, 89 tentacle(s) 68, 92–4, 108, 125, 131, 186, 216, 217 test (silica-based shell) 37, 38, 164, 217 “tethered” sea squirt 7 Thomson, Charles Wyville 51, 51, 197–8 Tiburonia, see big red jelly tidal currents 18, 19 Titanic, RMS 13, 170, 171, 171 toothed whale, see Cuvier’s beaked whale Townsend Cromwell, R/V 98 The Trenches 7, 8, 12, 13, 15, 16, 19, 165, 174, 174, 177–8, 178, 179, 196, 198, 205, 210, 212–15, 217 Triassic period 70, 117, 216, 217 Triceratops 47, 88 Trieste 6, 168, 208–11, 213 Tsunemi Kubodera, Dr 92, 94 tube worms 7, 59, 139, 142–3, 143, 144–7 Twilight Zone 8, 13, 14–15, 16, 26, 47, 55, 65, 107, 126, 154, 158, 174 Tyrannosaurus rex 44, 88

Strasburg, Donald 98

U

stromatolites 7, 74–9, 217 submersibles 16, 16, 17, 50, 80–3, 92, 168–73, 189, 208–11, 213, 215, 216, 217 sulphide 144

vampire squid 6, 35, 55, 66–9, 112, 128 viperfish 110–13 volcanoes 36, 139, 164

Stegosaurus 143 striated frogfish 132

Valdivia, SS 66

undersea vehicles 6, 14, 16, 16, 17, 50, 80–3, 92, 114, 136, 139, 140, 144, 162, 168–73, 189, 208–11, 209, 209, 213, 215, 216, 217

222

W

walruses 154, 154 Walsh, Don 208, 209, 210 whale pump 20–3, 21 whalefalls 7, 114–17, 121, 150, 183 whaling 21, 22, 23 Woods Hole Oceanographic Institution 171 worms 7, 8, 51, 52, 55, 55, 59, 110, 114–17, 116, 117, 121, 139, 142–3, 143, 144–7, 150, 175, 182, 189, 192

X

Xenacanthus 32 xenophyophores 162, 215

Y

yeti crabs 7, 140–1, 142

Z

Ziphius, see Cuvier’s beaked whale zooplankton 21, 107, 217

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Craig Lambert Photography/Alamy Stock Photo, 154 Tryton2011/Shutterstock,

Photo, 44 Public Domain, 45 Bluehand/Shutterstock (top), Nature Picture Library/

155 Wirestock Creators/Shutterstock, 156 Public Domain, 157 OpenCage Creative

Shutterstock (bottom), 46-47 Gerard Lacz/Shutterstock, 48-49 Azoor Photo/Alamy

Commons Attribution-Share Alike (top), Andrea Izzotti/Shutterstock, 158 Library

Stock Photo, 51 Well/BOT/Alamy Stock Photo (left), The Natural History Museum/

Book Collection/Alamy Stock Photo, 159 Andrea Izzotti/Alamy Stock Photo, 160

Alamy Stock Photo (right), 53 NASA/Alamy Stock Photo, 54 Alan Sirulnikoff/

Hectonichus via Wikimedia Commons, 161 Geography Photos/Universal Images

Science Photo Library, 55-57 Dotted Yeti/Shutterstock, 58 Public Domain, 59 Dante

Group, 162-163 Falconaumanni via Wikimedia Commons, 165 Blickwinkel/

Feolio/Science Photo Library, 60-61 Leonid Serebrennikov/Alamy Stock Photo, 62

Alamy Stock Photo (top), DeAgostini/Getty Images (bottom), 166 Universal History

Yuri Photolife/Shutterstock, 63 Danny Ye/Shutterstock/Shutterstock (top), World

Archive/Universal Images Group (top), 167 Scenics & Science/Alamy Stock Photo,

History Archive/Alamy Stock Photo (bottom), 64 The Natural History Museum/

168 Getty Images/Bettmann, 169 Science History Images/Alamy Stock Photo,

Alamy Stock Photo, 65 Universal History Archive/Universal Images Group via

170 Woods Hole Oceanographic Institution, 172-173 Kirt L. Onthank, Creative

Getty Images, 66 Zip Lexing/Alamy Stock Photo, 67 Rawpixel, 68 Adisha Pramod/

Commons Attribution-Share Alike, 175 ThreeArt/Alamy Stock Photo, 176 Silke

Alamy Stock Photo, 69 Ewald Rübsamen via Wikimedia Commons, 71 cbpix/Alamy

Baron, 177 Nhobgood via Wikimedia Commons, 178 Catmando/Shutterstock, 179

Stock Photo, 72 Reinhard Dirscherl/Alamy Stock Photo, 73 Nick Veasey/Science

The Five Deeps Expedition, 180-181 Nature Picture Library/Alamy Stock Photo,

Photo Library, 75 Robert Harding/Alamy Stock Photo, 76 Fossil & Rock Stock

182 David Chapman/Alamy Stock Photo, 183 MNHN, 184 Simon Brockington/

Photos/Alamy Stock Photo (top), Corbin17/Alamy Stock Photo (bottom), 77 Mark

Shutterstock, 185 Cbimages/Alamy Stock Photo, 187 Adisha Pramod/Alamy Stock

Garlick/Science Photo Library, 78-79 Tagliaferri Photography/Alamy Stock Photo,

Photo, 188 David Shale/Nature Picture Library, 189 Image courtesy of Journey into

81 Bettmann/Getty Images, 82 Sueddeutsche Zeitung Photo/Alamy Stock Photo, 83

Midnight - Light and Life Below the Twilight, 190-191 Nature Picture Library/

Granger Historical Picture Archive/Alamy Stock Photo, 84 Corbis/Getty Images,

Alamy Stock Photo, 193 Kikujungboy CC/Shutterstock, 194 Tony Wu/Nature

85 Martin Almqvist/Alamy Stock Photo, 86-87 Chokswatdikorn/Shutterstock,

Picture Library, 195 Ted Kinsman/Science Photo Library (top), Tony Wu/Nature

89 Marko Steffensen/Alamy Stock Photo (top), Alamy Stock Photo (bottom left),

Picture Library (bottom), 196 History and Art Collection/Alamy Stock Photo, 197

Granger Historical Picture Archive/Alamy Stock Photo (bottom right), 90-91

Mansell Collection/The LIFE Picture Collection/Shutterstock, 198-199 NHM

Kelvin Aitken/VWPics/Alamy Stock Photo, 93 Classic Images/Alamy Stock Photo,

Images, 200 Science & Society Picture Library/SSPL/Getty Images, 202 Alexander

94 David McNew/Getty Images, 95 Calimax/Alamy Stock Photo (top), Reuters/

Vasenin, 203 Ernst Haeckel, 204 Richard Bizley/Science Photo Library, 205 Phil

Alamy Stock Photo (bottom), 96-97 By Wildestanimal/Getty Images, 99 Blue Planet

Degginger/Science Photo Library, 206-207 Stocktrek Images, Inc/Alamy Stock

Archive/Alamy Stock Photo (top left), Doug Perrine/Alamy Stock Photo (bottom

Photos, 208 Everett Collection Inc/Alamy Stock Photo, 209 Ralph Sutherland

left), Personnel of NOAA Ship PISCES (right), 101 Dotted Zebra/Alamy Stock Photo

via Wikimedia Commons, 210-211 US Navy/Science Photo Library, 212 Science

(top), VTR/Alamy Stock Photo (bottom), 102 Eric Broder Van Dyke/Alamy Stock

History Images/Alamy Stock Photo, 213 U.S. Naval History and Heritage Command,

Photo, 103 Minden Pictures/Alamy Stock Photo, 105 Nature Picture Library/Alamy

214-215 US Geological Survey/Science Photo Library

Stock Photo, 106 Mauritius Images Gmbh/Alamy Stock Photo, 107 Morgan Trimble/ Alamy Stock Photo, 109 NOAA, 110 Dante Fenolio/Science Photo Library, 111

Every effort has been made to acknowledge correctly and contact the source and/

Mauritius Images Gmbh/Alamy Stock Photo, 112-113 Dante Fenolio/Science Photo

or copyright holder of each picture and Welbeck Publishing Group apologises for

Library, 115 NOAAA/Craig Smith (top), Subphoto.com/Shutterstock (bottom),

any unintentional errors or omissions, which will be corrected in future editions

116 Adisha Pramod/Alamy Stock Photo (top), Mark Conlin/Alamy Stock Photo

of this book.

223