Composition and Seasonal Succession of Phytoplankton of Taganrog Bay in the Sea of Azov and the Downstream Reaches of the Don River under a Changing Climate

The results of a study of phytoplankton in Taganrog Bay in the Sea of Azov and the downstream reaches of the Don River carried out in January–November 2017 are presented. A total of 210 species of eukaryotic algae and cyanoprokaryotes are identified. An analysis of the taxonomic, ecological, and geographical composition of the plankton algal flora and seasonal dynamics of biomass of phytoplankton taxonomic and size structures has revealed no changes in the ratio of large taxonomic and ecological–geographic groups in the algal flora when compared with previous years (1980s to early 2000s). However, the proportion of myxotrophic phytophagellates, cyanoprokaryotes from the planktotrichet complex, and small species increased in algal communities. It is shown that the water salinity is the main factor influencing the formation of species richness and total biomass and structure of phytoplankton. The maximum diversity and biomass of phytoplankton are recorded in the horohalinicum zone.