Lionard M, Roy S, Tremblay-Létourneau M, Ferreyra GA
mesocosm, Ultraviolet-B radiation, temperature, phytoplankton, global warming, St Lawrence, Quebec, Canada, 2 m3
The combined effects of increased UV-B and temperature on natural marine phytoplanktonfrom the St. Lawrence Estuary (Canada) were examined in an 8 d mesocosm experimentcarried out in Rimouski (Québec, Canada) in August 2008. We tested the hypothesis that in -creased temperature (+3°C) will offset algal growth suppression by UV-B (78% UV-B increase)using duplicate mesocosm experiments containing natural phytoplankton assemblages. The re -sponse of the entire phytoplankton community, in terms of HPLC pigment-based phytoplanktonbio mass, community composition (CHEMTAX), xanthophyll cycles photoprotection and quantumyield of photosystem II (the ratio of variable to maximum fluorescence: Fv/Fm), showed a significantinfluence of temperature (negative on small phytoplanktonic cells,