Phytoplankton of the St. Anna Trough: Influence of Abiotic Factors

— Samples were collected in the area of the St. Anna Trough in the northern Kara Sea in September 2015 and July–August 2016. Based on salinity and temperature distribution, four areas have been distinguished: the shelf adjacent to the St. Anna Trough, the shelf edge, and the upper and lower parts of the continental slope. The variability of the structure of phytoplankton communities has been analyzed in view of environmental conditions in the distinguished areas. It is shown that changes in the species structure of phytoplankton are more associated with seasonal reorganization in the community than with the effect of river runoff and waters of the Barents Sea and Atlantic. In the shelf area, the presence of Barents Sea winter water led to an increase in the number of species of early spring diatoms and an increase in the abundance of early and late spring diatoms. An increase in the abundance and biomass of phytoplankton and changes in their vertical distribution in mid-July–early August occurred against the effect of Barents Sea and Atlantic waters on the area and desalination of the upper layer under the effect of river runoff in early September.