Invasion of Lake Ontario by the Ponto-Caspian predatory cladoceran Cercopagis pengoi

Cercopagis pengoi, a waterflea native to the Ponto-Caspian region, was discovered during 1998 in Lake Ontario. Individuals were found throughout the lake during summer snagged on sportfishing lines. The population included parthenogenetic (92%) and sexual (2%) females and males (6%). Cercopagis has a very long caudal appendage that is more than five times the body length and terminates in a distinctive loop. Females and males from Lake Ontario were significantly smaller than individuals from the Neva Estuary, Baltic Sea. In Eurasia, C. pengoi occurs in relatively warm fresh and brackish waters (0-14 parts per thousand) at population densities usually <3000 individualsm.m(-3); mean and maximum population densities in Lake Ontario were 170 and 322 individuals.m(-3), respectively. The presence of females with resting eggs indicates that Cercapagis will likely establish in Lake Ontario. As with other recently introduced invertebrates, Cercopagis likely was transported to the Great Lakes in ballast water from eastern Europe. The rapid influx of Ponto-Caspian species into the Great Lakes warrants further study including identification of source populations, mechanisms of dispersal, impacts on recipient ecosystems, and efficacy of ballast water exchange programs.