Long-term changes of macrozoobenthos in the Eastern Gotland Basin and the Gulf of Finland (Baltic Sea) in relation to the hydrographical regime

摘要: Abstract Changes in the macrofauna of sub-halocline bottoms Eastern Gotland Basin and Gulf Finland during 1965–1994 period have been studied relation to salinity oxygen regimes. The study covers several significant major inflows North Sea water, as well longest stagnation last hundred years, with semi-permanent anoxia affecting distribution community structure macrozoobenthos. At beginning vast areas below halocline were devoid benthic macrofauna. water 1975–1976 led rapid recolonisation down approximately 150 m depth Basin, where conditions had improved, but no effect on macrozoobenthos communities Finland. subsequent, prolonged, 1977–1993 caused a deterioration consequence formation hydrogen sulphide (70–250 m) areas. Later, recovery was observed 70–100 zone when vertical stratification weakened intensified mixing resulted improved at these intermediate depths. this process most pronounced 1993–1994 highest levels Deep since 1930s. Consequently, 1994 polychaetes found 243 indicating even deepest part basin. fluctuations also affected marine species. biological significance hydrographical regime, potential impact eutrophication balance deep waters, consistency long-term data sets are discussed.