(Table 4) Mesozooplankton abundance and biomass and relative percentage of key zooplankton groups along the Bulgarian coast, Black Sea

Results of studies during Project of an international expedition onboard R/V Vladimir Parshin in September-October 2005 are presented. Intensive development of Bacillariophyceae and Dynophyceae was recorded in coastal waters of Bulgaria, Turkey, and in the Danube River delta during period of investigations. Increase in algae population was accompanied by rising of chlorophyll a concentration up to 2.0-5.5 µg/l. In the deep water region it did not exceed 0.5 µg/l. Phytoplankton growth rate in the surface water layer varied from 0.1 to 1.0 1/day. This parameter and NO2+NO3 concentration, as well as the silicon concentration were correlative, as was described by the Michaelis-Menten equation. Phytoplankton growth was affected by basic nutrients. Zooplankton grazing varied from 0.10 to 0.69 1/day and average values in different regions varied by 1.5 times. Microalgae size range is one of major factors of grazing regulation. Rate of phytoplankton consumption was decreasing with increasing the largest diatom Pseudosolenia calcar-avis impact on total biomass of nano- and microphytoplankton.