The habitat of Crangonyx pseudogracilis in the Upper Rhine region, Germany (Crustacea: Amphipoda): an invasive species is colonizing waters out-side the anthropogenically influenced main shipping channel

The North American amphipod Crangonyx pseudogracilis Bousfield, 1958 was recorded at 19 localities at the Upper Rhine, Germany, between 2004 and 2006. The habitats were different waters in the Rhine floodplain, mostly small ponds influenced by the dynamic of the river. The species is the first invasive amphipod in Germany colonising smaller more natural freshwater habitats.