COMPOSITION AND DISTRIBUTION OF PICOPHYTOPLANKTON ON THE OPEN AREA OF THE BLACK-SEA IN WINTER

Studies of picophytoplankton have been carried out on the open area of the Black Sea in February-April 1991 with concominant blooming of diatoms. During the working period cyanobacteria dominated in picoplankton comprissing an average 98.8% of the total picophytoplankton abundance and 95% of the total picoplankton biomass. The maximum number of cells reached up 1.5 x 10(9) cell/l in the east part of the Black Sea in February. Picoplankton biomass decreased during the period of observations. The values varied from 452 to 4918 mg/m2 (mean = 1632 mg/m2) in February-March and from 4 to 656 mg/m2 (mean = 190 mg/m2) in March-April. Picoplankton vertical distribution was determined by the upper margin of the main pycnocline. The largest part of the picoplankton biomass occured in the mixed lager. Since the seasonal pycnocline appearance in the last days of March the maximum biomass occured under the upper mixed layer. The relationship between blooming Nitszchia delicatula and picoplankton was not observed.