Peculiarity of phytoplankton distribution in the Baltic sea in early spring of 1990

The phytoplankton investigations in the open Baltic waters during cruise 25 of R.V ''Professor Schtockman'' (30.01-03.03.90) showed a low total level of their development (9600 cells l(-1) and 16 mg m(-3) on the average), Diatoms dominanted in the southwestern region in the beginning of February and March (1210-3080 cells l(-1) and 22.8-25.1 mg m(-3)). Blue-green algae - Aphanizomenon flos-aquae dominanted in the central part and to the south of Stockholm (15200-42000 cells l(-1) and 20.6-6.4 mg m(-3)). A. flos-aquae was in the stage of logarithmic growth to the east of Gotland in the zone of cyclonic upwelling. Phytoplankton was in the winter condition (2040 cells l(-1) and 7.2 mg m(-3)) in the northern region. The comparison of our data with the results of previous researches in the 80es showed the changes of phytoplankton composition connected with eutrophication of the Baltic waters: a very early beginning of vegetation of phytoplankton, especially A. flos-aquae. The thickness of the trophogenetic layer was decreasing because of the surface development of bluegreen algae and total decreasing of transparency.