COMPOSITION AND DISTRIBUTION OF PICOPHYTO PLANKTON 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 dia toms. During the working period cyanobacteria dominated in picoplankto n comprissing an average 98.8% of the total picophytoplankton abundanc e and 95% of the total picoplankton biomass. The maximum number of cel ls 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 observat ions. 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-Apr il. Picoplankton vertical distribution was determined by the upper mar gin of the main pycnocline. The largest part of the picoplankton bioma ss occured in the mixed lager. Since the seasonal pycnocline appearanc e in the last days of March the maximum biomass occured under the uppe r mixed layer. The relationship between blooming Nitszchia delicatula and picoplankton was not observed.