Spatial Organization of the Ecosystem in the Russian Sectors of the Baltic Sea in Summer

This paper is focused on the spatial distribution of environmental indicators in the Russian sectors of the southeastern Baltic Sea region and the Gulf of Finland during the extremely warm summers of 2021 and 2022 in the long-term absence of “major inflows” of the North Sea waters. The hypoxia and anoxia development in relation to self-sustaining eutrophication is discussed. In the deep waters of the southeastern part of the Baltic Sea, accumulations of fine suspended matter, largely consisting of manganese and iron oxyhydroxides, provide a habitat for chemosynthetic bacteria. The chlorophyll a concentration indicates that surface waters were predominantly mesotrophic in both areas, and an integrated primary production of phytoplankton was higher in clearer waters of the southeastern Baltic Sea region. Invasive zooplankton species were found in both areas.