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 210 Pb 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 reported from North American coastal waters. The probable vector for introduction of T. baltica was ballast water exchange and the successful establishment attributed to this taxon's euryhalinity tolerance.