Changes of biological communities in the Eastern Gulf of Finland during the last century

Abstract

Changes in biological diversity of the Neva Estuary (eastern Gulf of Finland), which is one of the largest Baltic estuaries, were assessed by means of BSRP SGEH priority indicators. They include macrophytobenthos, macrozoobenthos, alien species, ichthyofauna, avifauna, mammals and a portion of the territory covered by the protected areas. The most prominent biodiversity changes were observed in the upper freshwater Neva Bay, and moderate changes, in the lower brackish part of the estuary. Eutrophication, alien species and dredging activities are the major threats to biodiversity of the estuary. At present, alien species contribute about 8 per cent of species richness, however, 60-90 per cent of the biomass of bottom animals. Filamentous algae blooms affect biodiversity of zoobenthos in the shallow coastal zone. The climate-mediated fluctuations in near-bottom oxygen conditions are responsible for deterioration of zoobenthos in the open waters of the estuary. The decline of the benthic aboriginal crustaceans led to impairment of food conditions for fish and to a sharp reduction of their populations, which, in turn, was partly responsible for the population decline of ringed seals. Milder winters have also contributed to the decline in the numbers of this species. Dredging activities related to construction of new lands and ports are the main factor affecting fish, submerged macrophytes and waterfowl in Neva Bay. A considerable part of fish spawning grounds and waterfowl habitats in Neva Bay has been lost during the last decades. The long-term measures for conservation and improving of biodiversity should take into account periodicity of climatic changes and planned development of the region.