Factors describing the distribution of the zooplankton community in the Gulf of Finland in the context of interactions between native and introduced predatory cladocerans

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.