The first records of the occurrence of a North American invader

The amphipod species Gammarus tigrinus, Sexton 1939 is native to the Atlantic coast of North America. The native range of its occurrence includes oligo- and mesohaline brackish waters with salinity of up to 14‰. Our survey was carried out in the tributaries of the upper Vistula River in Upper Silesia that is the most urbanised and industrialised region in Poland and constitutes one of the largest coal basins in the world. This survey uncovered the first occurrence of G. tigrinus with the maximum density of 1040 individuals m−2 in the tributaries of the upper Vistula River that have been polluted by coal mine water discharge. The occurrence of the invasive alien gastropod species, i.e. Potamopyrgus antipodarum (Gray, 1843) was also recorded in such salinised water. Our results showed that the anthropogenically salinised tributaries of the upper Vistula River constitute new habitats for euryhaline species and create new migration routes for alien and invasive species.