Ecological Impact of Ponto-Caspian Invaders in the Baltic Sea, European Inland Waters and the Great Lakes: An Inter-Ecosystem Comparison

Abstract

We review the ecological impacts of Ponto-Caspian invaders in the Baltic Sea, selected lakes and rivers in inland Europe, and the North American Great Lakes. Each of these regions has been invaded multiple times in recent decades by Ponto-Caspian invertebrates and fishes. In attempt to identify predictable patterns, we compared the magnitude and direction of the impacts of these invaders on ecosystem components (phytoplankton, zooplankton, benthos and fish) and processes within each region. Most introductions appear to have increased local species richness rather than replace native species. Their impact on functional (rather than taxonomic) diversity, however, is of ecological importance. Ponto-Caspian organisms have become dominant members of various trophic levels (herbivores, detritivores and consumers) in benthic and pelagic food webs. They have apparently caused large-scale ecosystem impacts in the Great Lakes, whereas their role in Baltic Sea ecosystem is less pronounced, more spatially limited and, in part, camouflaged by other long-term ecological changes such as eutrophication. In all three regions, Ponto-Caspian invaders have altered multiple abiotic and biotic components and energy flow of ecosystems. Owing to the paucity of studies using pre- and post-invasion datasets, we cannot yet produce robust predictions for most of these invaders.