Hitch-hiking with diving boats: the risk of non-indigenous species dispersal in islands

The Portuguese archipelagos Azores and Madeira are located in a strategic position in the NE Atlantic being a stopover on marine routes between the European, African and American continents. Since 2014 there has been an increase in marine traffic to these islands and estimates indicate that this trend will continue to increase. Considering that the major vector of introduction of marine non-indigenous species (mNIS) in these archipelagos is marine traffic, and given the absence of legislation on hull biofouling management, the number of mNIS introduced in the marinas of these archipelagos is also expected to grow. Moreover, tourism intensification has brought more attention on seascapes increasing the number of recreational diving in these islands. The potential impact of recreational boating as a vector of NIS secondary spread has been already addressed but no studies have been conducted yet on the role of diving-boats in transport and local dispersion of mNIS, eg. from marinas to diving sites. In this context, we developed a model as a fuzzy inference system composed by three levels. In level one we evaluate the risk of each marina to act as mNIS source using as input variables: number of detected mNIS, marina cleaning frequency, presence of dry dock facilities and water disposal system, and proximity to commercial harbors; in level two, we assess each diving center’ risk to transport mNIS to diving spots using two variables: risk of home marina and diving-boat cleaning frequency; and in level three we calculate the risk of a diving spot to receive mNIS based on its visits’ frequency and on diving center’ risk. This model represents a valuable method to identify “high-risk” marinas; spreading risk by diving-boats and diving spot risk in the study area, thus enabling to prioritize actions for the diving centers to control mNis local spreading and promote the preservation of the protected marine habitats.