Impact of biological invasions on diversity and functioning of zooplankton communities in the estuarine ecosystems of the Baltic Sea (a review)

Long-term study of zooplankton in the Neva Estuary ecosystem, one of the largest urbanized gulfs of the Baltic Sea, revealed the actuality of biodiversity investigations related to the increasing role of unintentional introduction of invasive species of planktonic organisms into the aquatic ecosystems. Peculiarities of plankton communities in the Baltic estuaries were analyzed in relation to the problem of "biological pollution" and present-day viewpoint on the "paradox of brackish waters". It was shown that during 10 years since planktonic predator Cercopagis pengoi successfully invaded the eastern Gulf of Finland these crustaceans have not caused significant inhibitory effects on the high species diversity in this region of the Baltic Sea. The original method for the evaluation of the invaders' impact on zooplankton community elaborated by the author was verified using the data from Lake Ontario (North America). The study demonstrated the much stronger impact of Cercopagis on the aboriginal zooplankton community in Lake Ontario compared to the Neva Estuary ecosystem. Results of this investigation witness for the complexity of trophic interactions in the pelagic communities and specificity of their transformations under the impact of invasive species in aquatic ecosystems of different types.