Importance of ice algae and pelagic phytoplankton as food sources revealed by fatty acid trophic markers in a keystone species (Mytilus trossulus) from the High Arctic

摘要

The Arctic is characterized by strong seasonality in sea ice extent and temperature. To survive seasonal changes, species have different coping mechanisms. However, knowledge of how intertidal species cope with seasonality remains limited. To study this problem, we analyzed the fatty acid composition in the hepatopancreas and in the gill tissue of an intertidal temperate keystone species (Mytilus trossulus) at its northernmost limit in Greenland (77 degrees N). Fatty acid trophic markers (FATM) suggested that the diet mainly consisted of diatoms while the intertidal was covered by sea ice. During the following open-water period, food preferences shifted to pelagic dinoflagellates, and by the end of summer, food consisted of a diatom/dinoflagellates mixture. The contributions of macroalgae detritus, zooplankton and bacteria to the diet of M. trossulus were relatively low. We furthermore found that M. trossulus change membrane fatty acid composition in response to temperature changes in order to maintain functionality and avoid mortality. Membrane unsaturation significantly increased in response to decreasing temperatures as a result of selective retention of fatty acids from phytoplankton and from bacteria that on average constituted up to 24% of the total fatty acids. Our results provide novel insight on how a temperate species survives in the Arctic and thereby strengthen the knowledge needed to understand the potential for non-arctic temperate species to expand into the Arctic region.