Do harbours and nearby marinas share non-indigenous species? Examples from Northern Italy

The fouling community of three harbours (Genoa, La Spezia and Leghorn) and three neighbouring marinas (Santa Margherita Ligure, Lerici and Viareggio), in the Ligurian Sea and North Tyrrhenian Sea, were analysed in July 2013, for a total number of 63 samples collected from docks and pontoons. This systematic survey aimed at investigating the role of ports as sink and source habitat of non-indigenous marine species and the role of recreational boating in their secondary spread. A total of 261 macroinvertebrate species were identified, out of which 18 were non-indigenous species (NIS). In contrast with current belief, the 3 harbours do not seem “hotspots of introduction”, since the number of NIS in all sites was moderate (10 to 12 species). Moreover differences in richness of native species among the sites did not affect the number of NIS found, that were rather constant in all locations. The most frequent NIS were Hydroides elegans, Watersipora subtorquata, Hydroides dianthus, Zoobotryon verticillatum, Caprella scaura and Paranthura japonica that were common in harbours. Noteworthy records include: Watersipora arcuata, a Pacific cheilostome bryozoan new to the European coasts, was found in Santa Margherita Ligure marina; Grandidierella japonica, a Indo-Pacific amphiopod new to the Mediterranean Sea, was recorded in the marina of Viareggio; and Celleporaria brunnea, the cheilostome bryozoan already recorded in the Western Mediterranean Sea, was well represented in most of the localities. All marinas exhibited their own peculiar non-indigenous assemblages, independent from those observed in the nearby harbours