| Summary: | Abstract text: The Polar ecosystems are among those more threatened by the changing climate. The increase in temperature in the Arctic is being particularly alarming. Hardbottom polar coastal areas are densely populated by macroalgae, many of which are present even during the long winter period. A number of campaigns have been carried out in Kongsfjorden (Svalbard), and common macroalgae species have been tested for their ability to perform in an increased atmospheric CO2 and/or increased temperature scenario. We have shown that increased CO2 can modify the carbon balance of different species in different ways, affecting both their ability to cope with summer excess light and their internal composition, in a manner different to their cold-temperate ecotypes (North Atlantic). But the new weather conditions are also threatening their ability to overcome long dark winter periods, compromising the interannual survival. An increase in winter temperature of 4 C doubles the speed of thallus degradation and suppress the ability to generate new photosynthetic tissue. Taking into account that in western Svalbard the increase in winter temperature is about 3.6 C per decade, we might be close to see a drastic change in the community. Primary production has been measured by three different methods (O2 evolution, 14C fixation and PAM fluorometry), so uncoupling of photosynthetic processes have been revealed as part of the acclimation mechanisms. These adjustments allowed for the internal composition (carbohydrates, lipids and proteins) and growth being more resilient to the changing environment, so that acclimation is mainly taking part in the photosynthetic machinery. Photoinhibitory conditions occurring during the 24 h illumination during summer may explain some seasonal traits in these species. Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech.
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