Rate of species introductions in the Great Lakes via ships' ballast water and sediments

We report results from a study of species in ballast tanks of ships entering the Great Lakes between 2000 and 2002. We collected 1349 individuals from at least 93 unique taxonomic groups, of which approximately half were identified to species. We estimated that the zooplankton assemblage in ballast water destined for the Great Lakes comprised from 200 to 1000 unique taxa consisting of both freshwater and marine species. Between 14 and 39 of these taxa have not yet been recorded from the Great Lakes. Further, 13.9% of individual specimens identified to the species level were from species not previously collected from the Great Lakes. We collected seven nonindigenous freshwater species not currently found in the Great Lakes: Brachionus plicatilis, Cyclocypria kinkaidia, Maraenobiotus insignipes, Microcyclops rubellus, Microcyclops varicans, Neomysis awatchensis, and Paracyclops chiltoni. We found no evidence that ship age, seasonal timing, or age of ballast water affected the abundance of individuals or species in the ballast tanks. To our knowledge, these are the first extrapolations of data from ballast water collections to estimate the rate of species introduction to any ecosystem.