BIOGEOGRAPHY OF ALIEN AMPHIPODS OCCURRING IN IRELAND, AND INTERACTIONS WITH NATIVE SPECIES

Five alien species of amphipod Crustacea have arrived in Ireland this century. The terrestrial Arcitalitrus dorrieni (originally Australasian) and freshwater Crangonyx pseudogracilis (North American) were probably accidentally introduced with garden and garden-pond plants respectively. They had arrived by 1936 and 1969 (respectively), but have had very limited expansion of their ranges since then. The marine Corophium sextonae (originally from New Zealand) arrived by 1982, probably by natural means, from south-west Britain. The freshwater Gammarus pulex was deliberately introduced from Britain in the 1950s to enhance fisheries. However, the effects of this species on freshwater fish (as food source or in introducing parasites) have never been assessed. G. tigrinus was probably introduced accidentally from North America by ships during World War 1. These species are replacing the native G. duebenii celticus and G. lacustris, perhaps through a combination of interspecific and intraspecific predation, and greater population growth in certain biotopes. Despite its former abundance and ubiquity in Ireland, the long-term survival of G. d. celticus (a subspecies rare outside Ireland) appears threatened. The only other freshwater amphipod in Ireland, the subterranean Niphargus kochianus irlandicus is unique to Ireland, but too little is known of its biology and ecology to assess its status. The effects of the introduced species on the ecology of freshwater and terrestrial systems in Ireland remain unknown.