Ambivalence of Planktonic Invaders and Transformation of Communities

The ambivalence of planktonic invaders has been studied using the example of ecosystem effects of the invasive cladoceran Cercopagis pengoi (Ostroumov, 1891) in the Vistula Lagoon of the Baltic Sea. The influence of the invader on the taxonomic structure and productivity of plankton is studied. It is discovered that, in the long term, the predation pressure of C. pengoi on zooplankton has decreased; the abundance, biomass, and production of the dominant species of Rotifera, Cladocera, and Copepoda also declined. The ne-gative impact of C. pengoi on the planktonic community is reflected in a reduction in the food supply of juvenile Baltic herring and other planktivorous fish. The wide ecological niche of Cercopagis contributes to the expansion of its range, which can lead to a reduction in populations of phytophagous crustaceans, increased harmful algae blooms, and the further deterioration of the food supply of fish.