Phytoplankton of the Neva Bay and the Inner Estuary of the Gulf of Finland in 2001–2020

In 2001–2010 in the Neva Bay, as before since the beginning of the research (1980), the phytoplankton of the southern zone remained the richest, most diverse and highly productive. In the second decade, starting from 2014–2015, the indicators of phytoplankton biomass in the northwestern zone of the bay increased sharply in the summer period. In the inner estuary of the Gulf of Finland, in late July—early August, conditions favor development of planktonic algae in the epilimnion with a predominance of cyanobacteria capable of causing water blooming. The most significant quantitative change in phytoplankton species during the study period was among the cyanobacteria Planktothrix agardhii and the diatoms Skeletonema subsalsum. In the second decade of the studies, the biomass of phytoplankton in summer was about 7 mg/L everywhere. Contribution to eutrophication observed in the estuary comes from both anthropogenic and natural climatic factors.