ARMS in ports: monitoring non-indigenous species through Autonomous Reef Monitoring Structures.

Harbors and marinas are considered Non-Indigenous Species (NIS) hotspots, being departure and arrival points for numerous vessels and providing environments with less complex artificial substrates that promote NIS colonization. Monitoring changes in the structure of benthic communities allows to early detect the arrival of new NIS. In this study, we used Autonomous Reef Monitoring Structures, ARMS, 3D standardized passive collectors of benthic organisms, to monitor NIS presence and abundance in ports with different uses, a commercial harbor, and a touristic marina, in the northern Adriatic Sea, over one year. The sessile organisms growing on each ARMS plate were identify by photo analysis while the motile ones were morphologically recognized and counted using stereomicroscope. Benthic communities grown on ARMS were characterized by many taxa typical of coastal urbanized areas and showed high seasonal variability, being richer in spring and summer than in winter. Distinct benthic and NIS communities were found in the harbor and marina, with the marina hosting higher numbers of both native and NIS. This is likely due to the different environmental conditions, port structural complexity, and performed economic activities. Of the 86 macrofaunal taxa detected, nearly 19 % were NIS, mostly belonging to crustaceans, polychaetes, bivalves, and ascidians. Our results indicate that ARMS represent an efficient tool for monitoring NIS and suggest that they should be deployed in the spring season and in environments with different levels of urbanization to capture higher NIS diversity and enable their early detection.