Role of the type of boat traffic on the presence of sessile non-indigenous species (NIS) in marinas of southwestern Bay of Biscay

Abstract The aim of this study was to analyze the influence of the type of boat traffic on the settlement of sessile non-indigenous species (NIS) in marinas from southwestern Bay of Biscay. The research was conducted in two zones, and two marinas were selected in each zone. One marina was subjected to heavy traffic, with numerous large boats capable of making long trips, and the other was subjected to light traffic, with fewer and smaller boats of limited autonomy. At each port, 12 PVC plates were installed to favor the settlement of sessile organisms. Eleven out of the 36 identified species were NIS. The analysis of the faunal composition revealed that in the area where the two marinas were closer, it was not possible to distinguish a different community in relation to the type of traffic. The analysis of the ecological descriptors considering "traffic" and "zone" as explanatory factors indicated that the differences were significant only with respect to the second factor for most of them. Only NIS diversity was related to traffic, although its behavior was opposite in the two zones. Our results indicate that the type of traffic is not enough to explain the composition of the NIS communities in the region and that they tend to merge in the short term when small and large marinas are very close.