Plankton communities in the Neva Bay during the 20th century.

This study provides an overview on the phyto- and zooplankton studies made of the Neva Bay and of the changes that have taken place in the plankton community during the 20th century. It is known that plankton respond to changes in water quality, especially to changes in the content of organic matter. Comparisons of the literature data reveal the value of species as indicators of different conditions. Many plankton species in the Neva Bay show great year-to-year fluctuations due to varying environmental conditions. According to the results of studies conducted in 1911-1990, freshwater plankton species have dominated in the Neva Bay. The plankton community has essentially consisted of species transported from Lake Ladoga. Brackish-water species occasionally occurred in the plankton samples of the Neva Bay. High turbidity and rapid throughflow of water limit algal production in the bay and, due to the high outflow, the europhication effects of the catchment area are mainly conducted into the Gulf of Finland.