Modeling biofouling from boat and source characteristics: a comparative study between Canada and New Zealand

Abstract

In marine systems subject to vessel traffic, the likelihood of an invasion by an exotic species typically increases with the arrival of each infested boat. In this paper, recreational boating activity patterns and boat fouling by tunicates were compared between eastern Canada and central New Zealand, and the relative importance of boat characteristics on fouling was evaluated using Boosted Regression Tree analysis. For Canada, we also determined the relative importance of boat characteristics and propagule exposure (i.e., the interaction between tunicate density in source region and time in water) on patterns of boat fouling. Approximately half of boats examined during the fall in eastern Canada and during the summer in central New Zealand were fouled by tunicates. Although there was a greater richness of tunicate species on New Zealand boats, the two countries had several species or genera in common, including Botryllus schlosseri, Ciona spp. and Botrylloides spp. The time since last boat maintenance was longer in New Zealand than in Canada. However, boat fouling and boat-mediated spread may be facilitated in Canada by boating activity patterns there, as the movement of boats among multiple marinas is considerably greater than in New Zealand. Among the boat characteristics, voyage type, the time that boats spent in water (Canada) and time since last application of antifouling paint (New Zealand) were among the best predictors of boat fouling. However, our results from Canada showed that propagule exposure was more important than boat characteristics in predicting the presence of the invasive colonial tunicate, B. schlosseri. This study shows the importance of small boats as potential vectors for tunicates and demonstrates that predictive models for the spread of biofouling species should be based on regional boating patterns, boating characteristics, and local propagule exposure.