Molecular identification of the invasive cladoceran Cercopagis pengoi (Cladocera: Onychopoda) in stomachs of predators

Cercopagis pengoi , a recent invader to the Baltic Sea and the Laurentian Great Lakes, is recognized as an important prey for native fish. Its contribution to diets of other zooplanktivores has not been addressed so far, mostly because of the inadequacy of microscopic methods for diet analysis of aquatic invertebrates. To detect remains of C. pengoi in the guts of predators, a DNA‐based method and new species‐specific primers, amplifying a 154‐bp fragment of mitochondrial 16S rDNA gene, were developed and tested. This approach allowed identification of C. pengoi in stomachs of Neomysis integer , a common Baltic mysid, and is likely to be useful for diet analysis of other predators, both invertebrates and vertebrates, in a variety of trophic studies. Apart from obtaining a useful indicator of species identity in animal diets, these findings contribute to a growing body of evidence that C. pengoi successfully integrates into food webs in the invaded ecosystems and represents novel prey not only for fish but also for invertebrate zooplanktivores.