The impact of temperature nutrients and UVBR explained 18.8%, 11.0% and 8.4% of the variance of the small eukaryotes structure respectively. While Bouvy et al. (2011) could not detect any significant responses of pico- or nano-eukaryotic plankton in the same experimental conditions, we demonstrated here, at a different taxonomic resolution, that small eukaryotes community structure

was actually affected by this multi-factorial pressure. The simultaneous use of molecular and morphological methods was therefore essential to provide evidence of rapid shifts that occur at various taxonomic levels (abundance of large groups or community composition at OTU level) under the influence of temperature, UVBR and nutrient treatments. Among the 3 regulatory factors tested, both sequencing and CE-SSCP demonstrated 4-Hydroxytamoxifen ic50 that increased temperature had the greatest influence on the small eukaryote community structure and composition. The single effect of temperature (without any significant interaction with UVBR and nutrients) on total pigmented

eukaryote abundance was observed by microscopy. Considering the different phylogenetic groups within pigmented eukaryotes, complex interaction effects were also suggested. For instance, our results showed that under multi-factorial environmental changes, the general impact on the molecular diversity and abundance of pigmented Dinophyceae resulted Thiamine-diphosphate kinase from complex interactive (non-additive) effects. Alpelisib price Multi-factorial interactions were also apparent for Cryptophyceae which experienced antagonistic effects of nutrient

addition (significantly negative impact) and temperature (positive impact on relative abundance). In addition to the manipulated factors (temperature, UVBR and nutrients), some biotic interactions such as predation, viral lysis and competition, are involved in the responses observed in this experiment. For example, the general reduction of Mamiellophyceae (Micromonas and Ostreococcus) in all treatments might be linked to (i) manipulation effects since these fragile cells might have been affected by filtration steps, (ii) limitation by inorganic nutrients under the rather low orthophosphate concentrations at T96h (from 0.05 to 0.08 μM of PO4), (iii) the grazing impact of heterotrophic flagellates: these YM155 purchase microorganisms are known to play a significant role in the regulation of Ostreococcus populations in the Thau lagoon [56] and were shown to exert a strong control of bacterioplankton during the study period [24]. We could not detect a link between the dynamics of Micromonas/Ostreococcus and viruses.