Grandidierella japonica Stephensen, 1938 has appeared in a Mediterranean marina (Tuscany, Italy): first signals of invasion?

The aorid amphipod Grandidierella japonica is native to the Western Pacific region (Japanese archipelago) and known since the 1970's as introduced to the Pacific coasts of America; more recently, it appeared in the Atlantic coasts of Europe, with isolated records from England, Sweden and France. The present work reports the first record of G. japonica in the Mediterranean Sea, where no other species of the genus Grandidierella are known. More than 200 specimens of G. japonica were collected from the docks of the marina of Viareggio (Tuscany, Tyrrhenian Sea) in July 2013. G. japonica was present in seven out of nine sampling sites, 6 of which in the innermost part of the marina, characterized by brackish water conditions (water salinity ranged from 15.8 to 20.9 psu). Although previous introduction events of this species have been polyvectic (oyster trade and shipping), in the case of Viareggio, lacking any aquaculture facilities nearby, recreational boating is the only possible vector of introduction. In Europe, G. japonica is currently confined in few localities, mainly estuaries, enclosed bays and brackish water areas, but its successful history of invasion in the Pacific coasts of North America suggests that a further spread can be expected in the Mediterranean Sea as well.