Structure and Distribution of Autumn Zooplankton in the Southeastern Baltic Sea in 2015

Specific features of the structure and distribution of autumn zooplankton in the southeastern Baltic Sea (SEB) in October 2015 have been found taking into account the hydrological and hydrochemical data. No changes have been detected in the taxonomic composition of phyto- and zooplankton, including the increase in the number of stenothermic and stenohaline species as well as significant differences in the hydrological parameters compared to the long-term similar data. This indicates the absence of the impact of the winter Major Baltic Inflow in December 2014 on SEB plankton the following autumn. The level of phytoplankton vegetation in the upper homogeneous layer (125 000 ± 39 000 cells/L, 664 ± 143 mg/m3) is higher compared to the long-term data. The abundance and biomass of zooplankton (5100–16 800 ind./m3 and 49–143 mg/m3) are within the typical values for autumn in the SEB area. The features of the spatial zooplankton distribution are determined by trophic resources and the thermohaline structure of the water column.