Detection and prevention of biological invasions in marinas and ports: Epibionts and associated fauna of Mytilus galloprovincialis revisited

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Ports and marinas are gateways for introduction of non-indigenous species through ‘shipping’ worldwide. These anthropogenic environments concentrate a variety of artificial structures and substrates that are colonized by different types of organisms, being prone to biological invasions. One the most outstanding taxa in European marinas and ports are the mussels of the genus Mytilus. Mussels live in patches forming a three-dimensional, multi-layered and permanent biosubstrate that favours the settlement of sessile and mobile fauna, creating a perfect environment for the establishment and development of different species. In this study we characterized the biodiversity associated to the mussel patches of M. galloprovincialis in the Marina of Gijón (northern Spain, Cantabrian Sea), according to their status (i.e., native, introduced or alien, invasive and cryptogenic). The samples were collected from different areas of the marina: the outer dock (with national and international traffic), the middle dock and the inner one (both with local and national transit). We identified a total of 102 species associated to M. galloprovincialis, from which 13 and 4 species were invasive and alien respectively. The exotic fanworm Branchiomma luctusoum is reported for the first time in the Bay of Biscay and the Cantabrian Sea. The inner dock was the area with the highest number of non-indigenous taxa. Most of the alien and invasive species belonged to the groups Ascidiacea and Bryozoa, all of them filter feeders with great plasticity and ecological tolerance. Furthermore, the elemental composition microanalysis of the invasive bryozoan Watersipora subatra showed high levels of aluminium (a common element in marinas, being present in the fuel and in ship paintings), which may imply a risk of aluminium bioaccumulation in the environment. From these results we can conclude that mussel patches may facilitate the settlement and development of non-indigenous species in marinas, highlighting the importance of monitoring these mussel aggregations as a management tool for the early control and prevention of marine bioinvasions.