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 monthlyat six sites in the Gulf of Finland during six ice-free seasons.The abundances of different zooplankton taxa were related totemperature, salinity, eutrophication level (total nitrogen andphosphorus), phytoplankton Chl a and density of predatorycladocerans, including the non-indigenous Cercopagis pengoiand the native Leptodora kindtii. The results indicated thatvariability in the zooplankton communities was correlated notonly with predation by mesozooplankton but also with bottom-upeffects. Predation by the non-indigenous C. pengoi may significantlyaffect the dynamics of Cladocera and Rotatoria in the Gulf ofFinland during the summer season.