Mesozooplankton communities were studied monthly at six sites in the Gulf of Finland during six ice-free seasons. The abundances of different zooplankton taxa were related to temperature, salinity, eutrophication level (total nitrogen and phosphorus), phytoplankton (Chl a) and density of predatory cladocerans, including the non-indigenous Cercopagis pengoi and the native Leptodora kindtii. T he results indicated that variability in the zooplankton communities was correlated not only with predation by mesozooplankton but also with bottom-up effects. Predation by the non-indigenous C. pengoi may significantly affect the dynamics of Cladocera and Rotatoria in the Gulf of Finland during the summer season.
The Lake Miedwie vendace feeding was studied in summer 2000. The vendace food was found to contain 7 zooplankton species, Leptodora kindtii being a clear dominant in terms of weight, abundance, and frequency. The L. kindtii domination was maintained throughout the period of study. In late summer, stomachs of females contained less food than those of males did. The observations are discussed against a backdrop provided by results of an earlier zooplankton study.