The Predatory Water Flea Cercopagis Pengoi in the Baltic Sea: Invasion History, Distribution and Implications to Ecosystem Dynamics

Abstract

Cercopagis pengoi, a predatory cladoceran from the Ponto-Caspian basin, invaded the north-eastern Baltic Sea in 1992 due to ballast water discharges, and by the end of the 1990s formed several permanent populations in different gulfs and lagoons of the sea. The present-day distribution of C. pengoi witnesses for its high ecological plasticity. Evaluation of predation pressure of C. pengoi on its potential preys (younger larval stages of copepods, Daphnia spp., Bosmina spp. and rotifers) demonstrated significant impact of this alien species on native zooplankton communities and the pelagic food webs in general. A considerable dietary overlap of C. pengoi and planktivorous fish may contribute to a decline of food resource for important commercial fish - herring and sprat. On the other hand, during the population maximum, C. pengoi forms an important portion of the diet of these fish. This invasion has increased species diversity of the pelagic fauna of the Baltic Sea and incorporated an additional element to the trophic link of carnivores in the pelagic food web. Due to high population densities in some localities and considerable predation pressure on plankton communities, invasion of C. pengoi is likely to cause important structural and functional ecosystem alterations in the Baltic Sea.