Microbial eukaryotic distribution in a dynamic Beaufort Sea and the Arctic Ocean CONNIELOVEJOY * AND MARIANNEPOTVIN

temperature to salinity stratification of the upper water column. This change coincides with a faunal change as Pacific and Bering Sea zooplankton and fish species are replaced by Arctic species. The clear changes in distributions of larger organisms suggest that the Arctic is an ideal environment to test hypothesis of endemism in single-celled planktonic groups. Here, we investigate the distribution of phylotypes of small protists identified by their 18S rRNA gene. We constructed nine new clone libraries from three different water masses from samples collected along the continental shelf and offshore of Beaufort Sea, Western Canadian Arctic. The new data combined with all other available sequences from the Arctic were used to identify possible phylotypes with restricted Arctic distributions. Among those only reported to date from the Arctic were an oligotrichous ciliate, a chlorarachniophyte and a rhizarian. In the near-surface shelf sample, we also retrieved sequences from Pacific species that had not been previously reported in the Arctic. The occurrences of those phylotypes were best explained by incursions of Pacific Water as coastal currents in combination with elevated temperatures in 2005 that would have been favourable to the non-Arctic phylotypes. Overall, we found support for the notion of microbial biogeography and our results suggest that the Arctic may be vulnerable to microbial community changes