A review of Gobiid expansion along the Danube-Rhine corridor – geopolitical change as a driver for invasion

Five Gobiid fish species have recently increased their ranges along the Danube/Rhine river corridor. Studies to date, however, have tended to be local, site specific and reactive, examining just one or few species. As such, overall range has tended to be assumed based on a summary of patchy, and sometimes contradictory, data. This study provides an up-to-date literature review of first records of occurrence for all five species along their expansion route. In addition, available shipping data are examined to identify possible proximal causes of introduction. Three main discontinuous population centres were identified; all at or near important container ports: Vienna, Duisburg and Rotterdam. Shipping is confirmed as an important factor in the rapid national and international expansion of Ponto-Caspian Gobiids, with downstream drift, rip-rap and heavy boat traffic contributing to rapid spread on the Rhine. Geopolitical factors, however, such as the fall of communism and the Balkan conflict, have been key in influencing where, when, and by which route gobies first appear. Rapid expansion of Gobiids in the Rhine raises the possibility of establishment throughout mainland Europe via two new potential invasion corridors across Germany/Poland and France.