Range expansion of Ponto-Caspian peracaridan Crustaceans in the Baltic Sea basin and its aftermath: lessons from Lithuania.
Ponto-Caspian peracaridan Crustaceans first invaded the Baltic Sea basin from the basin of the Black Sea via artificial canals in the 18th Century. In the 1960s, the number of these species substantially increased due to deliberate introduction of Mysids and Amphipods into Lithuanian waters to enhance fish production. Range expansion of Ponto-Caspian peracaridan Crustaceans is continuing due to secondary dispersal and invasion by new species. Historically the main invasion vectors were inland shipping, deliberate introductions and natural dispersal across inland waterways; more recently the significance of marine invasions related to shipping seems to be increasing. These invaders have had detrimental impacts on local macroinvertebrates and may even have caused local extinctions of native species. Such impacts likely result from predatory and competitive interactions between alien and native species. The magnitude of predatory impacts of omnivorous Ponto-Caspian peracaridan Crustaceans can rise with increasing productivity of the environment. These Crustaceans, especially large-sized species, have proved to be prone to carnivorous feeding and high plasticity when acquiring nutrients for reproduction and growth. It seems that stoichiometric plasticity related to their flexible feeding strategy may favour their invasiveness. Another undesirable outcome of these invasions is distortion of conventional metrics of ecological status for aquatic systems. Meanwhile, at least in lakes, the primary goal of introduction, i.e. enhancement of fish production, has not been achieved. Some invasive Crustaceans seem to be adapting to previously unsuitable habitats in their invaded range, which may exacerbate their negative impacts. Further expansion of accumulated and new Ponto-Caspian peracaridan Crustaceans can be expected in Lithuanian waters as well as in the Baltic Sea basin, and their impacts may increase in the future.