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

Cercopagis pengoi, a waterflea native to the Ponto-Caspian region, was disc overed during 1998 in Lake Ontario. Individuals were found throughout the l ake during summer snagged on sportfishing lines. The population included pa rthenogenetic (92%) and sexual (2%) females and males (6%). Cercopagis has a very long caudal appendage that is more than five times the body length a nd terminates in a distinctive loop. Females and males from Lake Ontario we re 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 individual sm.m(-3); mean and maximum population densities in Lake Ontario were 170 an d 322 individuals.m(-3), respectively. The presence of females with resting eggs indicates that Cercapagis will likely establish in Lake Ontario. As w ith other recently introduced invertebrates, Cercopagis likely was transpor ted to the Great Lakes in ballast water from eastern Europe. The rapid infl ux of Ponto-Caspian species into the Great Lakes warrants further study inc luding identification of source populations, mechanisms of dispersal, impac ts on recipient ecosystems, and efficacy of ballast water exchange programs .