Further observations on the distribution and biology of two alien Amphipods, Gammarus tigrinus Sexton, 1939, and Crangonyx pseudogracilis Bousfield, 1958, in the Netherlands (Crustacea, Amphipoda)

Like in many previous years, the distribution pattern of G. tigrinus was followed. G. tigrinus proves to have recovered from its decline after the severe winter of 1978/1979. Likewise the distribution of C. pseudogracilis was checked, three year after its first discovery in the Netherlands. Some minor range extensions were found. In a monthly sampling program and in laboratory experiments information was collected on the biology so far unknown for this species. Its possible future interaction with local amphipod species is discussed.