HETEROTROPHIC PHYTOPLANKTON OF THE BLACK- SEA - SPECIES COMPOSITION AND SPATIAL-DISTRIBUTION

Species composition and spatial distribution of heterotrophic phytopla nkton was studied in autumn 1992 in the open waters of the Black Sea. Total phytoplankton biomass changed from 8 to 30 g/m(2). Principal spe cies were: autotrophic Ceratium fusus and Rhizosolenia calcar-avis. He terotrophic phytoplankton consisted of 17 dinoflagellates species. Its biomass comprised up to 13% of the total phytoplankton biomass. Speci es diversity was higher in the eastern part of the sea in comparison w ith the western one. Among-heterotrophic phytoplankton the most abunda nt species were Pronoctiluca pelagica and Ceratium fusus. They contrib uted to total heterotrophic algae biomass from 12 to 93% and from 1.7 to 60%, respectively. Population of C. fusus was simultaneously made u p from autotrophic and heterotrophic cells. Predominance of autotrophi c cells in the population occurred in the regions of the eastern and t he western cyclonic gyres. On the contrary, heterotrophic cells domina ted in the center of the sea and in the eastern part of the Rim Curren t. Similarity in spatial distribution of heterotrophic Pr. pelagica an d of autotrophic C. fusus was found. It was also confirmed by positive correlation between their biomasses.