Arctic sea ice algae differ markedly from phytoplankton in their ecophysiological characteristics Ane Cecilie Kvernvik1, Clara Jule Marie Hoppe2, Michael Greenacre3,8, Sander Verbiest4, Jozef Maria Wiktor5, Tove Gabrielsen6, Marit Reigstad7, Eva Leu8 1The Department of Arctic Biology, University Centre in Svalbard, Svalbard Science Centre, N-9171 Longyearbyen, Norway; 2Marine Biogeoscience, Alfred Wegener Institut – Helmholtzzentrum für Polar- und Meeresforschung, 27570 Bremerhaven, Germany; 3Department of Economics and Business, Universitat Pompeu Fabra and Barcelona Graduate School of Economics, Ramon Trias Fargas 25-27, 08005 Barcelona, Spain; 4Department of Earth Sciences, Faculty of Geosciences, Utrecht University, Utrecht 3584 CB, The Netherlands; 5Institute of Oceanology, Polish Academy of Sciences, 81-712 Sopot, Poland; 6Department of Natural Sciences, University of Agder, 4604 Kristiansand, Norway; 7Department of Arctic Marine Biology, The Arctic University of Norway, 9019 Tromsø, Norway; 8Arctic R&D, Akvaplan-niva AS, Fram Centre, 9296 Tromsø Author for correspondence: Ane Cecilie Kvernvik Tel: +47 98018439 Email:
[email protected] Running head: Ecophysiological characteristics of Arctic microalgae 1 Abstract Photophysiological and biochemical characteristics were investigated in natural communities of sympagic (ice-associated) and pelagic algae, in order to understand their respective responses towards variable irradiance and nutrient regimes. This study revealed large differences in photosynthetic efficiency and capacity between the two algal assemblages. Successful photoacclimation in sympagic algal assemblages was restricted to very low irradiance ranges, and as irradiances increased, photochemical damage and oxidative stress appeared to overweigh cellular defenses, causing a decline in photosynthetic performance under the highest irradiance levels (> 8 μmol photons m-1 s-1). On the contrary, pelagic algae assemblages were strongly light limited within the same irradiance ranges.