Small boats as vectors of marine invasion: experimental test of velocity and desiccation as limits

Secondary transport of introduced species can be important in dispersing potentially invasive species, and vectors of transport are often the fouled hulls of small fishing and recreational boats. Likelihood of transport depends on many factors, including resistance of the species to drag forces due to boat velocity and resistance to desiccation. To experimentally test the importance of drag on transport, we attached plates with a preexisting, 4 months old, assemblage of species, on a boat hull that was then subjected to one of three speeds (5, 15 and 20 knots) for 20 min. We experimentally tested desiccation tolerance with colonized plates that were exposed to the air for 3–132 h, after which they were examined for living organisms. A total of 35 taxa were identified, including introduced species, in southern Brazil: the barnacles Amphibalanus amphitrite, A. reticulatus and the octocoral Stragulum bicolor. In the drag experiment, all species survived transport. In the desiccation experiment, most species survived more than 6 h (fewer species much longer) of exposure to the air. Our results illustrate that a variety of taxa and growth forms can be transported over regional scales at speeds and travel conditions typical of small boats. They can also survive desiccation conditions typical of overland transportation of small boats. Thus, we recommend that additional management mechanisms must be put in place to reduce the probability of invasion due to secondary transport.