Gammarus tigrinus Sexton, 1939

9. Gammarus tigrinus Sexton, 1939 View in CoL

Description and illustrations: Sexton 1939, pp 545-548, pls IV-VI; Bousfield 1973, pp 51- 52p. 50, pl. IV-14; Lincoln 1979, p. 254, fig. 117.

This species belongs to a group of primarily American brackish- and fresh-water Gammarus species, which in many ways parallel the G. zaddachi group in Europe, i.a. by their conspicuous ‘tiger stripes’ (cf e.g. Bousfield 1969). G. tigrinus has no doubt been imported to Europe by man, but when and where is unknown. It was first discovered in Britain in the 1930’s and described as a new species by Sexton (1939). It was later recognized as identical to certain populations of the American freshwater species G. fasciatus Say, 1818 but this species was split by Bousfield (1958), with the brackish water populations retaining the name G. tigrinus . Later it was imported by fisheries people to both the Netherlands and Germany, in the hope that this would increase the food basis for freshwater fish; instead the species quickly developed into a problem (see i.e. Ruoff 1968). Its dispersal in the Netherlands has been followed in detail over the years, and it is clear that G. tigrinus is completely dominant to the indigenous Gammarus species in many habitats; it is i.e. less sensitive to pollution (see e.g. Nijssen & Stock 1966, Gras 1971).

Ecology and habitat: In the USA Gammarus tigrinus is a species of oligohaline and mesohaline habitats in estuaries. In Europe it is found in similar biotopes, e.g. in the Baltic Sea, but also in stagnant oligohaline brackish and even in fresh water, where it often has ousted the local indigenous Gammarus species.

Distribution: In Europe hitherto found in Ireland, Britain, Holland, Germany and the Baltic Sea. Gammarus tigrinus has not yet been recorded from Norway.