43 - Benthic Habitats and Benthic Communities in Southeastern Baltic Sea, Russian Sector

Abstract

The southeastern Baltic Sea (SEB) is a part of an intracontinental shelf basin of the Atlantic Ocean, located within a large depression of the Baltic Shield and Russian plate of the East European Platform. The Baltic Sea underwent several stages of development, from a freshwater ice-lake to semi-enclosed brackish-water sea. Such development was a result of climatic change, gradual melting of the ice sheet, eustatic sea-level rise, and glacio-isostatic uplift of the Baltic Shield. Broadscale geomorphic features of the area are lagoon plain, shallow water area, gentle slope, and relatively deep water area of the Gdansk Deep (sea depth 80–110 m). The dissolved oxygen content of bottom water in the Gdansk Deep is close to zero. Salinity, nutrient concentration, and oxygen condition in water layers below the halocline are influenced by periodical North Sea inflows. Ecological condition is far from pristine. Moderate nutrient loading, intensive shipping, limited fisheries, the presence of exotic species, oil-drilling platform with underwater pipelines, and three underwater cables all affect the environmental condition of the study area. Two broad groups of benthic habitats are soft-sediment bottoms (89% of surface area) and hard substrate (11%). Benthic faunal assemblages on hard substrata vary in terms of species diversity and abundance, but are dominated by sessile suspension feeders, whereas soft-bottom assemblages are dominated by selective and nonselective deposit feeders. Biodiversity and biomass reach maximum values on hard substrates located between 10 and 25 m water depth; benthos have been absent from depths >83 m in recent years due to oxygen depletion.