Colonization of the Laurentian Great Lakes by the Amphipod Gammarus tigrinus, a Native of the North American Atlantic Coast

Gammarus tigrinus, whose natural distribution is restricted to the North American Atlantic coast, has been found at numerous localities across the Laurentian Great Lakes. This amphipod was first discovered in Saginaw Bay of Lake Huron in 2002. However, analysis of archived samples and new material collected during 2001-2004 revealed that G. tigrinus is present in all of the Great Lakes. During August 2002, it occurred at an average density of 283 individuals·m−2 in Saginaw Bay, where it was outnumbered by the resident amphipods G. fasciatus and Hyalella azteca. In terms of frequency of occurrence, G. tigrinus was the second most numerous amphipod in beds of Typha in lower Great Lakes coastal wetlands during July 2004, being outnumbered only by native G. pseudolimnaeus. Gammarus tigrinus has a history of ballast water transfer in Europe and it likely exploited this transport vector during its recent colonization of the Great Lakes.