First Data on the Structure of Phytoplankton Communities of the East Siberian Sea

— Research on the structure of phytoplankton communities of the East Siberian Sea has been carried out during the 69th cruise of the research vessel Akademik Mstislav Keldysh within the framework of the Program “Ecosystems of the Siberian Arctic Seas”. The materials were obtained from 5th to 9th September at two quasi-meridional transects from inner shelf areas adjacent to the Indigirka and Kolyma mouths towards the outer shelf. The list of dominant algae groups and species, estimates of abundance, biomass and features of the vertical distribution of phytoplankton are given for pelagic biotopes with different environmental conditions. The significant quantitative deficiency of phytoplankton in the East Siberian Sea in the summer season in comparison with the Laptev Sea is determined, which is especially pronounced in the eastern area of the basin. The algae abundance along the Indigirka transect varies in the range of 11.9 to 66.3 × 10 3 cell/L, and the biomass from 16.4 to 339.1 mg/m 3 . The corresponding values for the Kolyma transect are 7.7–90.3 × 10 3 cell/L and 9.4–42.1 mg/m 3 . The maximum values along both transects are recorded in the area of the outer border of the river plume with increasing surface salinity up to 21–25 PSU. The material obtained makes it possible to reveal significant differences in the structure of phytoplankton communities of western versus eastern areas of the East Siberian Sea, which confirms the well pronounced zonal heterogeneity of the basin.