Diversity and distribution of heterotrophic flagellates in seawater of the Powell Basin, Antarctic Peninsula

Heterotrophic flagellates are essential components of the marine microbial food web. However, how the changes in flagellate populations reflect envi-ronmental changes in marine ecosystems is still unclear, especially in polar regions. In this study, we used pyrosequencing to examine the community structure of heterotrophic flagellates (HFs) in the Powell Basin's surface waters of the northern Antarctic Peninsula. OTUs (operational taxonomic units) of different taxa and the correlations between community structure and environmental factors were analysed. Eight taxa of HFs were selected for the principal analysis: Telonemia, Picozoa, Rhizaria, Amoebozoa, Apusomonas, Centrohelida, Choanomonada and marine stramenopiles (MASTs). The HFs were defined as heterotrophic picoflagellates (HPFs; 3 mu m) and heterotro-phic nanoflagellates (HNFs; 3 mu m, <20 mu m), which had similar dominant phyla (MASTs and Telonemia). However, their taxonomic composition dif-fered. Environmental factors exerted similar effects on the community struc-ture of both HPFs and HNPs. Compared with the correlation between HPF and environmental factors, the correlation between HNF and environmental fac-tors was stronger. Salinity, bacterial biomass and the biological interactions amongst dominant taxa were the main variables to influence the diversity and community structure of HFs.