Minor harbours as dispersal hubs in the Mediterranean Sea: The case of non–indigenous species in an Italian port

The Mediterranean Sea is one of the regions most severely affected by marine biological invasions, with maritime transport representing the principal pathway for the introduction and secondary spread of non-indigenous species (NIS). In this context, ports act as key nodes facilitating the establishment and dispersal of fouling- associated taxa. Nevertheless, small and medium-sized harbours remain poorly investigated. This study provides the first comprehensive assessment of NIS and cryptogenic invertebrates associated with the fouling communities of the port of Trapani (north-western Sicily, central Mediterranean Sea), a harbour directly connected to the Egadi Islands Marine Protected Area (MPA). The survey identified 27 taxa, with Peracarida and Polychaeta representing the most diverse components. To contextualise the findings, a Mediterranean-wide occurrence dataset was reconstructed through an extensive literature review. Species distributions were analysed across four Mediterranean biogeographical sectors, revealing strong spatial heterogeneity and marked geographical gaps in sampling effort, particularly along the North African coast. In parallel, maritime traffic data from the port of Trapani were analysed to evaluate potential pathways of dispersal. Results revealed intense liner and cruise vessel traffic connecting Trapani with several Mediterranean ports and transoceanic routes. The strategic position of Trapani, located between the Strait of Gibraltar and the Suez Canal, together with its proximity to the Egadi Islands MPA, highlights its importance as a potential stepping-stone hub for NIS dispersal in the central Mediterranean. Considering the ecological vulnerability of the neighbouring MPA, the high density of NIS recorded suggests a significant risk of spillover. Therefore, we recommend the implementation of early- detection protocols and a data-sharing system with the port authorities. Such management strategies are crucial to evaluate the progression of invasions from and towards this Mediterranean port and to mitigate the socio-economic and ecological impacts of NIS.