Thalassiosira baltica (Grunow) Ostenfeld (Bacillariophyta), a new exotic species in the Great Lakes

Microfossil analysis of sediment cores collected in 1994 and phytoplankton collected in 1998 from Lake Ontario indicated that the diatom Thalassiosira baltica (Grunow) Ostenfeld was introduced and became established ca. 1988 according to Pb-210 date estimates and has remained a predominant component of the phytoplankton since its establishment. Thalassiosira baltica is an exotic species in the Laurentian Great Lakes and is more commonly found in coastal brackish waters in western and northern Europe and only rarely repo rted from North American coastal waters. The probable vector for introducti on of T. baltica was ballast water exchange and the successful establishmen t attributed to this taxon's euryhalinity tolerance.