Monitoring Structures (ARMS) for monitoring non-indigenous species (NIS) in Ravenna Port

A Non-Indigenous Species (NIS) is defined as an organism, introduced by humans outside its natural past or present range of distribution, that successfully survives, reproduces, and establish in the new environment. Harbors and tourist marinas are considered NIS hotspots, as they are departure and arrival points for numerous vessels and because of the presence of free artificial substrates, which facilitate colonization by NIS. To early detect the arrival of new NIS, it is essential to monitor benthic communities in ports. Autonomous Reef Monitoring Structures (ARMS) are standardized passive collectors, composed of nine superimposed PVC plates, used to assess marine benthic communities. Ravenna (North Adriatic Sea) is one of the largest commercial seaports in Italy, with a canal port stretching 11 kilometers from the city center to the touristic marina. ARMS were deployed over 2021-2022 in two sites, the commercial port (Harbor) and the touristic marina (Marina), during three seasons (winter, spring, and summer) and left two meters underwater for three months. Percent cover of colonizing sessile communities was assessed by photographing plates and using PhotoQuad image analysis, creating a grid of 400 cells on the plate surface and selecting all cells in which a target taxon was present. While the abundance of the motile fraction (macrozoobenthos > 2 mm) was assessed by morphologically identifying the organisms using a stereomicroscope and light microscope, with emphasis on the detection and counting of NIS. Overall, 86 taxa were identified and 16 of them were NIS. Harbor hosts higher NIS richness than Marina during all the seasons. Benthic community structure differs significantly in both sites (Harbor, and Marina) and depending on sampling season (winter, spring, and summer). While differences between sites are related to their different environmental characteristic, anthropogenic pressures and kind of usage, differences among seasons seem related to the different spawning time of the main abundant species. For example, NIS peracarids Paracerceis sculpta (Holmes, 1904) and Caprella scaura Templeton, 1836 show a higher abundance during spring than during other seasons, while the NIS ascidian Ciona robusta Hoshino & Tokioka, 1967 shows a higher percent coverage during winter, according with its spawning periods. The use of ARMS together with different approaches to species identifications that can be in the future integrated with molecular identification methods (e.g, DNA barcoding and metabarcoding) represent a valuable tool for early detection of NIS and should be used routinely for long-term monitoring of their changes in presence and abundance.