Structure of the Baltic Sea phytocene under the conditions of progressive water eutrofication

Data on the phytoplankton distribution in the Baltic Sea during the autumn period were obtained from the processing of the materials collected during cruise 25 of RN Akademik Mstislav Keldysh (September 26-October 10. 1991). The zone of the Vistula hydrological front is distinguished by the high deg ree of development of total phytoplankton (2.3 million cell/l and 8 g/m(3) in the 0- to 1-m water layer). Here, the major mass of microalgae was compr ised by cyanobacteria. Tn the rest of the regions studied, the number of ph ytoplankton cells was smaller by two orders of magnitude, while their bioma ss was an order of magnitude lower. The variations of the overall abundance and biomass of phytoplankton in the 0-30-m layer in these regions were of the same order; their respective values in the coastal waters off Lithuania comprised 55 200 cell/l and 703 mg/m(3) and off the Sambian Peninsula 54 4 00 cell/l and 102 mg/m(3). In the northwestern region, corresponding values were 25 200 cell/l and 101 mg/m(3). In the Gulf of Gdansk, small centric s pecies of diatomaceous algae (Cyclotella spp.) dominated, while off the Lit huanian coasts, a predominance of large forms (Coscinodiscus granii) was ob served. However, while in the southeastern part (except for the hydrologica l frontal zone) diatoms dominated with respect to both cell number and biom ass, the northwestern part featured a predominance of cyanobacteria with re spect to cell number and dinoflagellates with respect to biomass. An analys is of the floristic similarity between the stations showed that, in the Bal tic Sea, a single integrated community with low similarity coefficients doe s exist.