A combined approach to understand trophic interactions between Cercopagis pengoi (Cladocera: Onychopoda) and mysids in the Gulf of Finland

Abstract

We use molecular markers, feeding experiments, and stable isotopes to understand trophic interactions between native mysids, Mysis mixta and Mysis relicta, and a recent invader to the Baltic Sea, the cladoceran Cercopagis pengoi. In feeding experiments, both mysid species ingested C. pengoi at a maximum of 16 prey mysid‐1 d‐1 and a specific consumption rate of 0.15 d‐1, similar to rates reported for predation on other prey species. The frequency of predation on C. pengoi assayed by molecular diet analysis of field‐collected mysids varied between 5% and 43% depending on mysid size and species. Surprisingly, it was consistently higher in juveniles than in adults and in M. mixta than in M. relicta. The results of stable isotope analysis corroborate those of feeding experiments and molecular analysis and indicate a higher contribution of C. pengoi to the nutrition of juveniles and M. mixta. These ontogenetic and interspecific differences in mysid predation on C. pengoi are likely to reflect differences related to their different migratory behavior. Thus, despite its low relative abundance, C. pengoi is readily consumed by mysids; this may impact lower food web interactions and the nutrition of mysids in the invaded ecosystems.