Settlement and potential for transport of clubbed tunicate (Styela clava) on boat hulls.

The invasive clubbed tunicate (Styela clava) was first identified in Georgetown harbor, Prince Edward Island (PEI), Canada, in 1998 and has since spread to other estuaries in PEI. Worldwide, the dispersal of this species is attributed to hull fouling and contamination of bivalve aquaculture products. We tested how clubbed tunicate settlement patterns differed among the most common boat hull surfaces and colors as well as the ability of these tunicates to survive extended atmospheric exposure similar to that of boats being transported on trailers during summer months. Untreated hulls made of fiberglass, painted wood, and bare aluminum were quickly colonized by larval tunicates with hulls painted black attracting significantly more colonists compared to white-painted hulls. Use of anti-fouling paint kept colonization to a minimum, even after 12 weeks in the water. Bare aluminum hull material attracted the highest numbers of tunicates, which is a problem because boats operating around bivalve aquaculture sites are mainly constructed of aluminum and cannot be painted with anti-fouling paint according to industry codes of practice. Aluminum and fiberglass hull material that had one-year-old tunicates growing on them were exposed to open air for 48 h during September (mean daytime high temperature 29.7˚C, night-time low 8.5˚C). Nearly all tunicates were alive after 8 hours with only 10 to 11 % mortality after 48 h. Based on a 48 h survival time, viable tunicates on boats removed from infested waters of PEI could be spread on boats transported on trailers to any waters within 1600-2000 km of PEI – a distance encompassing the entire Atlantic seaboard of Canada.