When I think of invasive animals that attach to boat hulls, colonial tunicates, coelenterates, barnacles and mollusks come to mind. All of these have motile larvae which swim to or are carried to the hull by water currents where they attach. Once attached, the organism metamorphoses into a sessile adult form. If scraped from the hull, the adult form has no means to reattach to another substrate and for all intents and purposes is culled from participating in the formation of motile larvae of the next generation of that species. Thus, scraping them from the hull not only cleans the hull but it could be effective in preventing establishment of new invasive species on other hulls or other substrates. Can you think of any invasive species which can reattach to another hull once scraped from the introducing hull? Am I back on topic, or is this purely a political rant?