Heterotrophic nanoflagellates in the pelagic zone and sediments of the eastern Laptev sea
For the first time, the species composition of heterotrophic nanoflagellates, their quantitative characteristics, as well as the abundance and biomass of their main food objects: bacteria and picophytoplankton, were determined in the water column and sediments of the Laptev Sea. On a meridional transect from the Lena delta to the deep-sea zone in early autumn an increase in the number and biomass of planktonic flagellates was recorded in the area of the internal shelf, which is impacted by Lena's freshwater input. The pattern of vertical distribution of planktonic flagellates differed in the different parts of the sea, but everywhere their greatest number was confined to either the surface or the near-bottom water layers. Quantitative parameters of planktonic flagellates positively correlated with the temperature, bacterial abundance and biomass and negatively correlated with the water salinity. The abundance and biomass of heterotrophic flagellates in the surface sediments was 3-4 orders of magnitude higher than in the water column and exceeded those of planktonic flagellates in the shallow sites under 1 m2. A total of 28 species and forms of heterotrophic flagellates have been identified. Representatives of two taxonomic groups: Kinetoplastea and Stramenopiles, which were the most tolerance to the salinity, dominated in the community. The species richness of the flagellates decreased with the water depth and was minimal in the less saline coastal waters and increased in the deep-see area.