Abstract
Cercopagis pengoi, a pelagic cladoceran native to the Ponto-Caspian region, has established permanent populations in the Baltic Sea. In the wake of large-scale consequences for biodiversity and ecosystem processes in the Great Lakes after invasion of this and similar species (Bythotrephes longimanus), an elucidation of potential effects of Cercopagis on native plankton species and fish in the Baltic calls for attention. In order to further understand effects of Cercopagis on zooplankton and fish species, we study its feeding and growth using most novel and sensitive methods: stable isotope analysis (for deriving a diet) and biochemical markers, i.e. RNA, DNA, and protein content (for growth assessment). Conventional methods (fish stomach analysis, zooplankton population analysis, and bioenergetics modelling) complement the study. Our results obtained by stomach content analysis of fish as well as by using stable isotope analysis of the pelagic food web suggest that trophic position of herring in the coastal areas of the northern Baltic proper has changed substantially after the invasion. With the central role of this species in the pelagic food web, this implies that the invasion by Cercopagis has resulted in a general food web change. To provide essential information for risk assessment of the invasion, further studies will evaluate the potential impact of Cercopagis on structural and functional biodiversity and significance of Cercopagis as a consumer and a prey for fish.
Sweden