Biology of Polar Benthic Algae 9783110229714, 9783110229707

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Marine and Freshwater Botany

Biology of Polar Benthic Algae Edited by Christian Wiencke

DE GRUYTER

Editor Prof. Christian Wiencke Department Seaweed Biology Section Functional Ecology Alfred Wegener Institute for Polar and Marine Research Am Handelshafen 12 27570 Bremerhaven Germany [email protected] This book has 36 figures and 22 tables. Front cover image The cover shows the endemic Antarctic brown macroalga Cystosphaera jacquinotii (Montagne) Skottsberg. Cystosphaera jacquinotii is the only member of the Fucales in the Antarctic. Its distinctive, elegant fronds reach a length of 3 m and have been found down to 50 m depth. The photo was taken in Potter Cove, King George Island, Antarctica (© Alfred Wegener Institute, Bremerhaven, Germany). ISBN 978-3-11-022970-7 eISBN 978-3-11-022971-4 Library of Congress Cataloging-in-Publication Data Biology of polar benthic algae / edited by Christian Wiencke. p. cm. – (Marine and freshwater botany) Includes bibliographical references. ISBN 978-3-11-022970-7 1. Marine algae – Polar regions. 2. Benthic plants – Polar regions. I. Wiencke, Christian. QK579.B56 2010 579.80 17760911 – dc22 2010037549 Bibliographic information published by the Deutsche Nationalbibliothek The Deutsche Nationalbibliothek lists this publication in the Deutsche Nationalbibliografie; detailed bibliographic data are available in the Internet at http://dnb.d-nb.de. © 2011 by Walter de Gruyter GmbH & Co. KG, Berlin/New York Printing and Binding: Hubert & Co. GmbH & Co. KG, Göttingen Printed in Germany www.degruyter.com The citation of registered names, trade names, trade marks, etc. in this work does not imply, even in the absence of a specific statement, that such names are exempt from laws and regulations protecting trade marks etc. and therefore free for general use.

To my wife Christine and our children Antje, Friederike and Jan-Christian

Preface This book on the Biology of Polar Benthic Algae is the outcome of investigations over about three decades in the Arctic and in the Antarctic carried out by scientists from all over the world. The main aim of the book was to synthesise the present state of knowledge and to develop perspectives as basis for future research. A preliminary version has been published already as a Special Issue of Botanica Marina (Vol. 52, Issue 6; 2009), edited by myself and Margaret N. Clayton (Monash University, Victoria, Australia). I would like to express my sincere thanks to my wife Christine for her ever-lasting encouragement, inspiration and patience throughout the years. Thanks go also to my collaborators, students and all other authors of this book for their contribution. Last not least I would like to thank my institution, the Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, for the strong support I received and the publisher for the opportunity to publish this book. Bremerhaven, October 2010

Christian Wiencke

List of contributing authors Adil Al-Handal Department of Marine Ecology University of Gothenburg P.O. Box 461 405 30 Göteborg, Sweden e-mail: [email protected]

Kai Bischof Department of Marine Botany University of Bremen Leobener Strasse, NW2 28359 Bremen, Germany e-mail: [email protected]

Charles D. Amsler Department of Biology University of Alabama at Birmingham Birmingham AL 35294-1170, USA e-mail: [email protected]

Gabriela Laura Campana Departamento de Biología Costera Instituto Antártico Argentino Cerrito 1248 (1010AAZ) Buenos Aires, Argentina e-mail: [email protected] and CONICET Rivadavia 1917 (1033AAJ) Buenos Aires, Argentina and Departamento de Ciencias Básicas (PIEA) Universidad Nacional de Luján Rutas 5 y 7 (6700), Luján Buenos Aires, Argentina

Margaret O. Amsler Department of Biology University of Alabama at Birmingham Birmingham AL 35294-1170, USA e-mail: [email protected] Bill J. Baker Department of Chemistry University of South Florida Tampa Florida 33620, USA e-mail: [email protected]

Margaret N. Clayton School of Biological Sciences Monash University Victoria 3800, Australia e-mail: margaret.clayton@ monash.edu

Inka Bartsch Department Seaweed Biology Section Functional Ecology Alfred Wegener Institute for Polar and Marine Research Am Handelshafen 12 27570 Bremerhaven, Germany e-mail: [email protected]

Ken Dunton Marine Science Institute University of Texas at Austin 750 Channel View Drive Port Aransas TX 78373, USA e-mail: [email protected]

Susanne Becker Department of Marine Botany University of Bremen Leobener Strasse, NW2 28359 Bremen, Germany e-mail: [email protected]

Suzanne Fredericq Department of Biology University of Louisiana at Lafayette Lafayette LA 70504-2451, USA e-mail: [email protected]

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Jana Fredersdorf Institute for Polar Ecology University of Kiel Wischhofstrasse 1 – 3 24148 Kiel, Germany and Institute of Marine Botany University of Bremen Leobener Strasse 28359 Bremen, Germany e-mail: [email protected] Anna Fricke Department Seaweed Biology Section Functional Ecology Alfred Wegener Institute for Polar and Marine Research Am Handelshafen 12 27570 Bremerhaven, Germany and Leibniz Center for Tropical Marine Ecology Fahrenheitstr. 6 28359 Bremen, Germany e-mail: [email protected] and Bremen International Graduate School for Marine Sciences “Global Change in the Marine Realm” (GLOMAR) Bremen International Graduate School for Marine Sciences Leobener Str. 28359 Bremen, Germany Ronnie N. Glud Southern Danish University Institute of Biology & Nordic Center for Earth Evolution (NordCEE) e-mail: [email protected] and Scottish Association for Marine Science (SAMS) Scottish Marine Institute Oban PA37 1QA, UK

and Greenland Climate Research Centre (c/o Greenland Institute of Natural Resources) BOX 570 3900 Nuuk, Greenland Iván Gómez Instituto de Biología Marina Universidad Austral de Chile Casilla 567 Valdivia, Chile email: [email protected] Dieter Hanelt Biozentrum Klein Flottbek University of Hamburg Ohnhorststr. 18 22609 Hamburg, Germany e-mail: [email protected] Max H. Hommersand Department of Biology University of North Carolina Chapel Hill NC 27599-3280, USA e-mail: [email protected] Pirjo Huovinen Instituto de Biología Marina Universidad Austral de Chile Casilla 567 Valdivia, Chile e-mail: [email protected] and Centro i-mar Universidad de Los Lagos Casilla 557 Puerto Montt, Chile Katrin Iken School of Fisheries and Ocean Sciences University of Alaska Fairbanks P.O. Box 757220 Fairbanks, AK 99775-7220, USA e-mail: [email protected]

List of contributing authors

Ulf Karsten Institute of Biological Sciences Applied Ecology University of Rostock Albert-Einstein-Str. 3 18051 Rostock, Germany e-mail: [email protected] Michael Kühl Marine Biological Laboratory Department of Biology University of Copenhagen Strandpromenaden 5 3000 Helsingør, Denmark e-mail: [email protected] Thomas Laepple Section Paleoclimate Dynamics Alfred Wegener Institute for Polar and Marine Research Bussestrasse 24 27570 Bremerhaven, Germany e-mail: [email protected] Peter Leopold Institute of Biological Sciences Applied Ecology University of Rostock Albert-Einstein-Str. 3 18051 Rostock, Germany e-mail: [email protected] James B. McClintock Department of Biology University of Alabama at Birmingham Birmingham AL 35294-1170, USA e-mail: [email protected] Richard L. Moe University and Jepson Herbaria University of California Berkeley CA 94720-2465, USA e-mail: [email protected]

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Markus Molis Department of Seaweed Biology Section of Functional Ecology Biologische Anstalt Helgoland Alfred Wegener Institute for Polar and Marine Research Marine Station Kurpromenade 201 27498 Helgoland, Germany e-mail: [email protected] Ruth Müller Department Seaweed Biology Section Functional Ecology Alfred Wegener Institute for Polar and Marine Research Am Handelshafen 12 27570 Bremerhaven, Germany and Section Adaptation and Climate LOEWE Biodiversity and Climate Research Centre Georg-Voigt-Straße 16 60325 Frankfurt/Main, Germany e-mail: [email protected] María Liliana Quartino Departamento de Ciencias del MarInstituto Antártico Argentino Dirección Nacional del Antártico Cerrito 1248, C1010AAZ Buenos Aires, Argentina e-mail: [email protected] and Museo Argentino de Ciencias Naturales “B. Rivadavia” Av. A. Gallardo 470 (C1405DJR) Buenos Aires, Argentina Ralf Rautenberger Institute for Polar Ecology Christian Albrechts University of Kiel Wischhofstr. 1 – 3, Building 12 24148 Kiel, Germany

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and Department of Botany University of Otago PO Box 56 Dunedin, New Zealand e-mail: [email protected]

Bettina Walter Department of Marine Botany University of Bremen Leobener Strasse, NW2 28359 Bremen, Germany e-mail: [email protected]

Michael Y. Roleda Institute for Polar Ecology University of Kiel Wischhofstrasse 1 – 3 24148 Kiel, Germany and Department of Botany University of Otago Dunedin 9054 New Zealand e-mail: [email protected]

Christian Wiencke Department Seaweed Biology Section Functional Ecology Alfred Wegener Institute for Polar and Marine Research Am Handelshafen 12 27570 Bremerhaven, Germany e-mail: [email protected]

Søren Rysgaard Greenland Climate Research Centre (c/o Greenland Institute of Natural Resources) Box 570 3900 Nuuk, Greenland e-mail: [email protected] Rhena Schumann Institute of Biological Sciences Applied Ecology University of Rostock Albert-Einstein-Str. 3 18051 Rostock, Germany e-mail: [email protected] Franciska S. Steinhoff Institute of Marine Botany University of Bremen Leobener Strasse 28359 Bremen, Germany e-mail: [email protected]

Jana Woelfel Institute of Biological Sciences Applied Ecology University of Rostock Albert-Einstein-Str. 3 18051 Rostock, Germany e-mail: [email protected] Angela Wulff Department of Marine Ecology University of Gothenburg P.O. Box 461 405 30 Göteborg, Sweden e-mail: [email protected] Katharina Zacher Department Seaweed Biology Section Functional Ecology Alfred Wegener Institute for Polar and Marine Research Am Handelshafen 12 27570 Bremerhaven, Germany e-mail: [email protected]

Contents 1. Introduction: Biology of polar benthic algae Christian Wiencke and Margaret N. Clayton . . . . . . . . . . . . . . . . . . . . . . . . . . . Environment, biogeography and biodiversity 2. The abiotic environment of polar marine benthic algae Katharina Zacher, Ralf Rautenberger, Dieter Hanelt, Angela Wulff and Christian Wiencke . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3. Biodiversity, biogeography and zonation of marine benthic micro- and macroalgae in the Arctic and Antarctic Angela Wulff, Katrin Iken, María Liliana Quartino, Adil Al-Handal, Christian Wiencke and Margaret N. Clayton . . . . . . . . . . . . . . . . . . . . . . . . . . 4. Notes on the systematics and biogeographical relationships of Antarctic and sub-Antarctic Rhodophyta with descriptions of four new genera and five new species Max H. Hommersand, Richard L. Moe, Charles D. Amsler and Suzanne Fredericq . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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Chemical ecology 5. Defenses of polar macroalgae against herbivores and biofoulers Charles D. Amsler, Katrin Iken, James B. McClintock and Bill J. Baker . . . . 101 6. Field studies on deterrent properties of phlorotannins in Antarctic brown algae Katrin Iken, Charles D. Amsler, Margaret O. Amsler, James B. McClintock and Bill J. Baker . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121 Primary production and ecophysiology 7. Benthic microalgal production in the Arctic: applied methods and status of the current database Ronnie N. Glud, Jana Woelfel, Ulf Karsten, Michael Kühl and Søren Rysgaard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8. Microphytobenthic biomass along gradients of physical conditions in Arctic Kongsfjorden, Svalbard Jana Woelfel, Rhena Schumann, Peter Leopold, Christian Wiencke and Ulf Karsten . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9. Phenology and seasonal physiological performance of polar seaweeds Christian Wiencke, Iván Gómez and Ken Dunton . . . . . . . . . . . . . . . . . . . . . . . 10. Light and temperature demands of marine benthic microalgae and seaweeds in polar regions Iván Gómez, Angela Wulff, Michael Y. Roleda, Pirjo Huovinen, Ulf Karsten, María Liliana Quartino, Ken Dunton and Christian Wiencke . . . . 11. Freezing tolerance and photosynthetic performance of polar seaweeds at low temperatures Susanne Becker, Bettina Walter and Kai Bischof . . . . . . . . . . . . . . . . . . . . . . .

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Polar benthic algae in a changing world 12. Impact of oceanic warming on the distribution of seaweeds in polar and cold-temperate waters Ruth Müller, Inka Bartsch, Thomas Laepple and Christian Wiencke . . . . . . . 13. Physiological responses of polar benthic algae to ultraviolet radiation Ulf Karsten, Angela Wulff, Michael Y. Roleda, Ruth Müller, Franciska S. Steinhoff, Jana Fredersdorf and Christian Wiencke . . . . . . . . . . 14. Drivers of colonization and succession in polar benthic macroand microalgal communities Gabriela Laura Campana, Katharina Zacher, Anna Fricke, Markus Molis, Angela Wulff, María Liliana Quartino and Christian Wiencke . . . . . . . . . . . . 15. Conclusion and outlook: Future perspectives on the investigation of polar benthic algae Christian Wiencke and Margaret N. Clayton . . . . . . . . . . . . . . . . . . . . . . . . . .

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Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 325 Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 329

1 Introduction Biology of polar benthic algae Christian Wiencke and Margaret N. Clayton

Motivation

The main motivation for this book and the special issue of Botanica Marina is to document the considerable progress that has been achieved during the last few decades in the biology of polar benthic marine algae. Following significant research outputs in the 1970s and early 1990s, the first review of the ecophysiology of polar phytoplankton, ice algae and seaweeds was published in 1995 by Kirst and Wiencke (1995). A subsequent review (Wiencke 1996) was centred on the investigation of Antarctic seaweeds. A synopsis on Antarctic seaweeds appeared in 2002 (Wiencke and Clayton 2002). More recently, Wiencke et al. (2007) summarised our knowledge of the life strategy, ecophysiology and ecology of seaweeds from the Arctic and Southern Oceans. This short list indicates that many new results were obtained on the biology of marine benthic seaweeds from polar waters during those years. In contrast, benthic microalgae from polar regions received little attention until recently, and their biology has not yet been reviewed. Moreover, all reviews published so far have been centered around basic research, and no attempt has been made to include the impacts of global climate changes on marine benthic algae, which are frequently regarded as the most important primary producers in Arctic and Antarctic coastal waters. Hence, the aim of this book is to synthesise the current state of knowledge and to present an outlook on the biology of marine benthic micro- and macroalgae from both polar regions. Following a summary of the environmental conditions in both polar regions, the focus of this book will be on biodiversity and biogeography of seaweeds and marine benthic microalgae. The recent progress in chemical ecology will be emphasised in a separate section before primary production and ecophysiology of polar benthic algae are discussed. The final section is devoted to the responses of polar benthic algae in a changing world. Reviews and original research articles are combined to summarise recent research and to give a brief overview of current investigations. It will become obvious, however, that many gaps still exist and these are addressed in most of the chapters and in an outlook at the end of this book.

Environment, biodiversity and biogeography

Reviews in this section deal with the state of knowledge of the abiotic environment inhabited by benthic algae (Chapter 2; Zacher et al. 2009), their biodiversity, biogeography and zonation (Chapter 3; Wulff et al. 2009) and include an original contribution by Hommersand et al. (2009; Chapter 4) describing several new taxa of Antarctic

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and sub-Antarctic red algae together with a much-needed appraisal of the systematics and biogeography of this highly diverse and ancient group. The environment of polar marine benthic algae is characterised by a strong seasonality of the light conditions and low temperatures. Nutrient levels in the Southern Ocean are high throughout the year, whereas nutrients are depleted in Arctic waters during summer. These and other abiotic factors strongly affecting polar algae are addressed in the review by Zacher et al. (2009; Chapter 2). This chapter also includes a summary of the presently occurring and expected changes in the environmental conditions due to global climate changes. The review by Wulff et al. (2009; Chapter 3) makes it clear that the systematics and biodiversity of the benthic microalgae of polar regions are poorly known and that further research is required before any conclusions can be drawn or any meaningful study of their biogeography is possible. In contrast, the more conspicuous and accessible polar macroalgae have been studied more intensively. The systematics of Arctic and Antarctic brown and green macroalgae and the commoner red algae are comparatively well known and it is well established that both macroalgal biodiversity and endemism are greater in Antarctica than in the Arctic and that this is explained by the contrasting biogeographical histories of the two regions. Experimental studies have shown that the local distribution or zonation of polar micro- and macroalgae is influenced by their responses to a range of environmental factors including their ability to resist and survive grazing. Chapter 4 by Hommersand et al. (2009) contains a timely update on the knowledge of the red algal flora of Antarctica based on recent collections made by Moe, Fredericq, Amsler and co-workers and includes descriptions of four new genera and five new species. Phylogenetic analyses of rbcL sequences are used as a basis for discussing the hypothetical biogeographic relationships of Antarctic red algae. The authors conclude that the composition of the Antarctic red algal flora can be attributed to vicariance resulting from plate tectonics and sea floor spreading and to long distance dispersal. They argue that climatic change over geological time and changes in ocean currents also influenced the composition of the present-day Antarctic algal flora.

Chemical ecology

This section comprises two chapters by Amsler et al. (2009; Chapter 5) and Iken et al. (2009; Chapter 6) dealing with recent research on the biotic interactions of polar macroalgae with herbivores and with biofouling organisms. Amsler et al. (2009; Chapter 5) argue in their review that chemical defences of Antarctic macroalgae, in particular against important amphipod mesoherbivores, appear to be of greater significance than physical defense mechanisms, in contrast to Arctic species whose physical defences may provide greater protection against herbivory. In addition, phlorotannins from some species of Antarctic macroalgae are shown to have antifouling activity against diatoms. Iken et al. (2009; Chapter 6) report directly on field studies examining the effect of phlorotannins from species of brown algae as deterrents against three different herbivores, a diatom and bacteria. They found that in general deterrent properties were specific to the algal species and also to the grazers, diatoms and bacteria tested.

Introduction: Biology of polar benthic algae

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Primary production and ecophysiology

This section comprises five chapters, three reviews and two original contributions. Two (Chapter 7, 8; Glud et al. 2009, Woelfel et al. 2009) deal with benthic microalgae, two (Chapter 9, 11; Becker et al. 2009, Wiencke et al. 2009) with macroalgae and one with both (Chapter 10; Gómez et al. 2009). The review by Glud et al. (2009; Chapter 7) makes it clear that the database on primary production of polar benthic microalgae is limited, as it is for biodiversity and biogeography of this algal group (Wulff et al. 2009; Chapter 3). The available data demonstrate, however, that Arctic benthic microalgae contribute significantly to productivity in coastal areas down to 30 m depth and exceed that in the pelagic zone. For the coastal Arctic ecosystem as a whole, the authors estimate a benthic microalgal contribution of between 1.1 and 1.6  107 t C year – 1. This enormous figure is based on a robust comparative analysis of all available datasets taking into account the various applied methods. The first data on microphytobenthic biomass in Kongsfjorden (Spitsbergen), a glacial fjord in the Arctic, are presented in the chapter by Woelfel et al. (2009; Chapter 8). On soft bottom substrata, chl-a varied depending on current/wave exposure and geographic location. The highest values were obtained close to the glaciers. Biomass doubled or tripled in shallow water between mid and late summer, but was comparatively stable during the season at greater depths. The data underline the importance of microalgae for marine benthic productivity in coastal waters of the Arctic, as also pointed out by Glud et al. (2009; Chapter 7). The phenology and physiology of polar seaweeds is strongly attuned to the extreme seasonal changes in daylength. This fact is revealed very clearly in the review by Wiencke et al. (2009; Chapter 9). Polar season anticipators grow and reproduce predominantly during winter and early spring. This strategy makes necessary a strong interrelation between seasonal photosynthesis and the formation and remobilisation of storage carbohydrates. Indeed, photosynthetic rates in almost all species studied are highest in spring when the light conditions are good. In kelps and kelp-like species, the photoassimilates formed are stored in summer as reserve compounds, and in winter and early spring they are translocated to the meristem to fuel growth. The light requirements for photosynthesis and growth of both polar macro- and microalgae are very low, allowing the algae to grow down to considerable depths (Chapter 10; Gómez et al. 2009). In seaweeds, the stages characterised by most efficient light use are microscopic, i.e., their spores and microscopic gametophytes. Similarly, benthic diatoms are strongly shade-adapted. In this context, it is not surprising that benthic diatoms and few-celled microscopic stages of seaweeds are able to withstand long periods of darkness. Antarctic seaweeds and – as far as we know – benthic microalgae from the Antarctic are adapted to low temperatures to a greater extent than species from the Arctic. These characteristics are based on special physiological and metabolic properties that allow benthic marine algae from both polar regions to make considerable contributions to coastal primary productivity, as pointed out above for benthic microalgae. A special focus in the investigation of polar seaweeds is seen in studies on the intrinsic freezing tolerance and photosynthetic performance of benthic algae at low temperatures. A pilot study by Becker et al. (2009; Chapter 11) of two eulittoral/upper sublittoral seaweeds from the Arctic and Antarctic shows that photosynthesis of Arctic

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Fucus distichus L. is remarkably insensitive to freezing. On the other hand, low water temperatures in combination with high irradiance severely affected photosynthesis of Palmaria decipiens (Reinsch) R.W. Ricker from Antarctica, prompting the need for more intensive studies on the interactive effects of various factors. Polar benthic algae in a changing world

Global warming due to the greenhouse effect and enhanced UV radiation due to stratospheric ozone depletion are major threats to marine life, especially in polar regions. The original contribution by Müller et al. (2009; Chapter 12) focuses on the effects of global warming on the geographic distribution of cold-water key structural seaweeds. For the first time, modelled changes of seawater temperatures in the 21st century have been used as basis for the prediction of changes in seaweed distribution. Fourteen species were studied and the result was that under the moderate scenario of temperature change, North Atlantic polar to cold-temperate seaweeds will extend their distribution into the high Arctic, but will retreat along the coasts of the northeastern Atlantic. In contrast, the southern hemisphere species studied will presumably not significantly change their geographic distribution. Several cold-temperate regions were identified where seaweed composition and abundance will certainly alter under the scenario tested. These changes will provoke substantial and cascading effects for biodiversity and functioning of seaweed-dominated ecosystems. The review by Karsten et al. (2009; Chapter 13) summarises our knowledge of the effect of UV radiation on the physiology and metabolism of polar marine benthic micro- and macroalgae. The cellular targets of UV radiation are various biomolecules, in particular the DNA and proteins, which directly absorb UV radiation or are indirectly affected by various UV-induced photochemical reactions, e.g., the formation of reactive oxygen radicals. In this way, photosynthesis and other cellular processes can be strongly inhibited. On the other hand, there is a considerable potential for acclimation to UV radiation through various repair and protective mechanisms. DNA damage can be repaired enzymatically, and oxidative stress is counteracted by enzymatic defence systems and scavenging by antioxidants. UV-absorbing substances such as mycosporine-like amino acids and brown algal phlorotannins may prevent damage. If damaging effects prevail, cell fine structure is damaged and growth, as well as reproduction, can be constrained, which can lead to severe ecological consequences. The ecological effects of UV radiation are an important element in the review by Campana et al. (2009; Chapter 14). Ambient UV radiation shapes the composition of polar seaweed communities during early succession and can exert persistent effects on later stages. In contrast to macroalgal propagules and germination stages, the UV-resistance of benthic microalgal communities is exceptionally high, which has positive implications for seaweed recruitment by providing UV-free space. In addition to UV radiation, other abiotic and biotic factors driving the structure of polar marine benthic algal communities are summarised. Primary succession starts with a rapid colonisation by diatoms and ephemeral macroalgae, whereas colonisation by perennial seaweeds is slower and highly seasonal. Global warming will presumably affect algal succession as increasing temperatures will affect the vitality of individual species and will promote the invasion of cold-temperate species, as pointed out also by Müller et al. (2009; Chapter 11). Retreating glaciers provide on the one hand open space for colo-

Introduction: Biology of polar benthic algae

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nisation, but change nutrient supply, reduce salinity, increase sedimentation and thereby decrease light availability. Altogether, this will affect algal succession and presumably lead to changes in structure and function of polar benthic communities. References Amsler, C.D., K. Iken, J.B. McClintock and B.J. Baker. 2009. Defenses of polar macroalgae against herbivores and biofoulers. Bot. Mar. 52: 535 – 545. Becker, S., B. Walter and K. Bischof. 2009. Freezing tolerance and photosynthetic performance of polar seaweeds at low temperatures. Bot. Mar. 52: 609 – 616. Campana, G.L., K. Zacher, A. Fricke, M. Molis, A. Wulff, M.L. Quartino and C. Wiencke. 2009. Drivers of colonization and succession in polar benthic macro- and microalgal communities. Bot. Mar. 52: 655 – 667. Glud, R.N., J. Woelfel, U. Karsten, M. Kühl and S. Rysgaard. 2009. Benthic microalgal production in the Arctic: applied methods and status of the current database. Bot. Mar. 52: 559 – 571. Gómez, I., A. Wulff, M.Y. Roleda, P. Huovinen, U. Karsten, M.L. Quartino, K. Dunton and C. Wiencke. 2009. Light and temperature demands of marine benthic microalgae and seaweeds in polar regions. Bot. Mar. 52: 593 – 608. Hommersand, M.H., R.L. Moe, C.D. Amsler and S. Fredericq. 2009. Notes on the systematics and biogeographical relationships of Antarctic and sub-Antarctic Rhodophyta with descriptions of four new genera and five new species. Bot. Mar. 52: 509 – 534. Iken, K., C.D. Amsler, M.O. Amsler, J.B. MacClintock and B.J. Baker. 2009. Field studies on deterrent properties of phlorotannins in Antarctic brown algae. Bot. Mar. 52: 547 – 557. Karsten, U., A. Wulff, M.Y. Roleda, R. Müller, F.S. Steinhoff, J. Fredersdorf and C. Wiencke. 2009. Physiological responses of polar benthic algae to ultraviolet radiation. Bot. Mar. 52: 639 – 654. Kirst, G.O. and C. Wiencke. 1995. Ecophysiology of polar algae. J. Phycol. 31: 181 – 199. Müller, R., T. Laepple, I. Bartsch and C. Wiencke. 2009. Impact of oceanic warming on the distribution of seaweeds in polar and cold-temperate waters. Bot. Mar. 52: 617 – 638. Wiencke, C. 1996. Recent advances in the investigation of Antarctic macroalgae. Polar Biol. 16: 231 – 240. Wiencke, C. and M.N. Clayton. 2002. Antarctic seaweeds. In: (J.W. Wägele, ed) Synopses of the Antarctic benthos 9. A.R.G. Gantner, Ruggell, Liechtenstein. pp. 239. Wiencke, C., M.N. Clayton, I. Gómez, K. Iken, U.H. Lüder, C.D. Amsler, U. Karsten, D. Hanelt, K. Bischof and K. Dunton. 2007. Life strategy, ecophysiology and ecology of seaweeds in polar waters. Rev. Environ. Sci. Biotechnol. 6: 95 – 126. Wiencke, C., I. Gómez and K. Dunton. 2009. Phenology and seasonal physiological performance of polar seaweeds. Bot. Mar. 52: 585 – 592. Woelfel, J., R. Schumann, P. Leopold, C. Wiencke and U. Karsten. 2009. Microphytobenthic biomass along gradients of physical conditions in Arctic Kongsfjorden, Svalbard. Bot. Mar. 52: 573 – 583. Wulff, A., K. Iken, M.L. Quartino, A. Al-Handal, C. Wiencke and M.N. Clayton. 2009. Biodiversity, biogeography and zonation of marine benthic micro- and macroalgae in the Arctic and Antarctic. Bot. Mar. 52: 491 – 507. Zacher, K., R. Rautenberger, D. Hanelt, A. Wulff and C. Wiencke. 2009. The abiotic environment of polar benthic algae. Bot. Mar. 52: 483 – 490.

Environment, biogeography and biodiversity

2 The abiotic environment of polar marine benthic algae Katharina Zacher, Ralf Rautenberger, Dieter Hanelt, Angela Wulff and Christian Wiencke

Introduction

In the polar regions, both light conditions and temperatures are exceptionally low for a large part of the year. Another important feature of polar regions is the strong seasonality, especially of the light regime, distinguishing the Arctic and the Antarctic from all other regions of the world. The present review gives an account of the environmental factors to which benthic marine algae are exposed in polar regions, explains differences between the Arctic and Antarctic and summarizes our present knowledge of global and anthropogenic changes on polar benthic ecosystems.

Differences between polar regions

While many environmental features are similar in the two polar regions, the Arctic and the Antarctic Oceans differ considerably in their origins, their cold-water history and their present environmental conditions. The Arctic Ocean is surrounded by continental land masses with a vast coastline that is continuously connected to the temperate coasts of America and Eurasia. In contrast, Antarctica is an ice-covered continent completely surrounded by the Southern Ocean without any land bridge to temperate regions since the late Mesozoic (Lüning 1990). A very important feature of the Southern Ocean amplifying this separation is the Antarctic Circumpolar Current (ACC), which flows in a clockwise direction around the continent driven by westerly winds (Lüning 1990). The ACC is thought to have developed 25 million years ago, thermally isolating the waters around the Antarctic continent. The Antarctic polar front (or Antarctic Convergence) delimits the Southern Ocean sharply to the north (Orsi et al. 1995). In contrast, the southern limit of the Arctic Ocean is poorly defined as the Arctic polar front is discontinuous and subject to strong variations (Clarke 1990). There is a considerable inflow of warm North Atlantic waters through the Fram Strait, where the West Spitsbergen Current mixes with Arctic waters. Another major feature differentiating the two polar regions is their different coldwater history. The water temperatures in the Southern Ocean have been low for 14 million years, following the first glaciation of East Antarctica (Crame 1993). By comparison, water temperatures in the Arctic decreased much later. Glaciation and a winter ice cover did not develop in the Arctic before 2 million years ago, at the beginning of the Pleistocene (Thiede 1986, Clarke 1990, Zachos et al. 2001). The Arctic Ocean is covered by multi-year pack ice, whereas the Southern Ocean pack ice is thinner

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Chapter 2

and most of it melts during summer. Due to these differences in oceanographic and geological features, the benthic algal communities between both polar regions have developed differently (Chapter 3, 10; Gómez et al. 2009, Wulff et al. 2009). The Antarctic marine seaweed flora is characterized by a high degree of endemism (33% in Antarctic seaweeds), whereas in the Arctic, only few endemic species have been found so far (Chapter 3; Wulff et al. 2009). The kelp forests formed by the Laminariales, present in temperate and Arctic regions, are completely absent in Antarctica. The same ecological niche is occupied in Antarctic regions by endemic Desmarestiales (Wiencke and Clayton 2002). Endemism of polar benthic microalgae remains to be studied (Chapter 3; Wulff et al. 2009). Seasonal changes of light conditions

At the northern and southern distribution limits of benthic algae in the Arctic and the Antarctic at 80 N and 77 S, respectively, the annual solar radiation is 30 – 50% lower than in temperate to tropical regions, and the polar night lasts for about 4 months (Lüning 1990). At lower latitudes, e.g., at the northern limit of the Antarctic region, around the South Shetland Islands, daylengths vary between 5 h in winter and 20 h in summer (Wiencke 1990). This seasonal variation of light conditions is extreme, with large associated variations in the coverage of sea ice and snow. The strongest seasonal variation in sea ice conditions is found in the Southern Ocean. Here, it increases from 4 million km2 in summer to 20 million km2 in winter (Thomas and Dieckmann 2002). In the Arctic, sea ice cover varies from 4 – 5 million km2 in late summer to 15 million km2 in late winter (Drobot et al. 2008). If the ice is covered by snow, irradiance directly below can be diminished to 5 or 10 m (Chapter 3; Wulff et al. 2009). In winter when the freezing sea surface (fast ice) meets the hard substratum, an ice foot is formed that encases the rock surface and the inhabiting biota (Barnes 1999). Due to tidal movements, its thickness increases. The ice foot may further raft sessile benthic algae away when it disintegrates in summer (Gutt 2001). Annual, less susceptible macroalgae such as Enteromorpha, Ulva, Ulothrix and Urospora remain attached to the rock or re-colonize denuded hard substratum quickly, within