<p>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, NW Spain. The research was conducted in two zones, and two marinas were selected in each one. One of the marinas was subjected to long-range traffic, with numerous large boats capable of faraway trips, and the other was subjected to short-range traffic, with smaller boats of limited autonomy. At each port, four sampling devices, each one consisting of three PVC plates, were installed to favor the settlement of sessile organisms. Eleven out of the 36 identified species were NIS. The analysis of the ecological descriptors considering “traffic” and “zone” as explanatory factors indicated that the differences in species richness and in the computed biodiversity indices were significant with respect to the second factor, but irrelevant regarding the type of traffic. NIS abundance was related to the type of traffic only in the western zone of study, but in the other one it was similar in the two marinas investigated; NIS diversity could not be related to any of the explanatory variables. The analysis of the sessile faunal composition revealed that it was not possible to distinguish a different community in relation to the type of traffic in the zone where the two marinas were closer to each other. Thus, our results indicate that the type of traffic is not enough to explain the composition of the NIS communities in the region.</p>