Easy Riders: non-indigenous Peracarids travelling across Mediterranean marinas

Recreational boating has proven to be a vector of introduction for non-indigenous species (NIS), by carrying organisms as part of the biofouling on the boat hull. However, this subject has been poorly studied in the Mediterranean Sea thus far. In our work, we focused on peracarid crustaceans as a model for studying dispersal and range expansion of NIS. In fact, peracarids commonly occurr in biofouling assemblages and have weak autonomous dispersal capability; thus their presence in non-native regions can be confidently attributed to human transport. Twenty-four marinas from seven countries were selected across the Mediterranean Sea, selected for their relevance as touristic hotspots and maritime connectivity. Fouling assemblage samples were collected in each marina from submerged structures as well as from the hulls of moored vessels. Peracarids were identified to species level, then classified by status as: “native”, “cryptogenic”, or “non-indigenous”. Nine NIS were recorded; four of which were new location records, highlighting range-expansion, and one NIS constituted a new Mediterranean record. About 1/3 of sampled boats were found hosting at least one non-indigenous peracarid species. Community similarities were found in marinas very distant from one another, hence suggesting that marinas are artificially connected by boating travel patterns. Additionally, the most common species in marinas and on boats were either cryptogenic, or NIS suggesting that the colonization process of NIS is favoured by continuous boat-mediated introductions and a lack of well-structured native communities inside the marinas. International strategies to avoid marine NIS dispersal via recreational boating are currently lacking. Further studies and increased awareness on this topic are required to better understand the strength of the recreational boating vector in order to design efficient strategies to control NIS introductions and spreading to help preserve Mediterranean marine biodiversity.