Within the genus Gammarus s.str., which is widely distributed throughout the northern hemisphere, more than 100 freshwater species can be distinguished.

After the introduction of Gammarus tigrinus in The Netherlands some 25 years ago and of other recently invading amphipods (Crangonyx pseudogracilis and Corophium curvispinum) the native species decreased, the invaders increased. The success of these invaders and its impact on the local amphipod fauna is discussed. Electrophoretic tests give evidence that a second invasion of Gammarus tigrinus, this time from Germany, is taking place. Some predictions about future developments are made.

No abstract

This part of the revision of the freshwater Gammarus species deals with the G. roeseli-group. Members of this artificial group are characterized by the presence of dorsal processes (carinae) on the metasome segments.