Structure and Dynamics of Plankton Communities in the Coastal Zone of the Curonian Lagoon of the Baltic Sea in 2017–2021 in the Period of Cyanobacterial Blooms

The structure and dynamics of plankton communities in the coastal zone of the Curonian Lagoon of the Baltic Sea from January to December 2017–2021 has been studied. It was found that, at the coastal shallow littoral station surrounded by macrophytes, the species diversity was higher and the quantitative characteristics of phytoplankton and zooplankton were lower in all seasons and years of the study than at the deeper coastal station located behind the macrophyte belt. The exception was the period when, as a result of surge events, the phytoplankton biomass in the coastal littoral in October–November 2018 increased to 326–627 g/m³. Every year, Cyanobacteria “blooms” with different intensities and durations were observed at the Lagoon. The abundance of cells of potentially toxic Сyanobacteria exceeded the World Health Organization standard, as a rule, in summer months at a deepwater coastal station, especially in 2017–2018. This had a negative impact on the state of the entire ecosystem, primarily on zooplankton organisms, in which communities the proportion of dead individuals increased. Water during the period of Cyanobacterial blooms in summer and autumn 2017–2018 also had an acute toxic effect on planktonic test organisms.