Long-term dynamics of zooplankton in the Baltic Sea in connection with the changes in water regime

Abstract

The dynamics of zooplankton abundance for the period from 1949-1974 depending upon the changes in phosphate quantity, thermal regime and other factors is considered. An increase of zooplankton amount in the upper 100 m layer connected with a considerable rise of phosphate content in the active (0-60 m) layer of the sea is determined. Qualitative changes in zooplankton composition lying in an increase of Cladocera and Rotatoria role in plankton in 1970-1974, as compared with 1949-1969, are pointed out. Plankton abundance in the deep-water layer (100-150 m) depends upon the oxygen content and a general level of zooplankton productivity. Small decrease in oxygen amount and a sharp increase in a general level of zooplankton productivity in 1970-1974 conditioned some rise in zooplankton abundance in 100-150 m layer, as compared with 1960-1969.