Transient small boats as a long-distance coastal vector for dispersal of biofouling organisms
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Alaska is at the northern end of an apparent latitudinal trend of decreasing coastal marine introductions on the West Coast of North America. Historical propagule supply may have played a role in forming this trend, but few studies have evaluated propagule supply to northern latitudes. Here, we examined the role of small boat traffic as a mechanism of long-distance spread for nonindigenous species (NIS) into coastal Alaska. We used a combination of public records, marina surveys, and boater interviews to characterize vessel traffic patterns and boater behaviors. In-water SCUBA sampling of recently arrived transient boats provided data on extent, richness, composition, and biogeography of biofouling incursions to Alaska from outside of the state. We documented a striking seasonality and directionality of vessel traffic, and most vessels were on voyages of >900 km. Most transient vessels sampled had few organisms, although one third had >100 organisms on submerged surfaces. Several NIS were recorded, including two that are not known to be established in Alaska (Watersipora subtorquata and Amphibalanus improvisus). The seasonal northward pulse of vessels and their cumulative biofouling species represent an important incursion mechanism for species yet to establish at the northern edge of a marine bioinvasion front in the northeastern Pacific. The low numbers of NIS sampled in this study coincide with the low number of marine NIS known from Alaska, which suggests that an opportunity remains to promote awareness and management of the vector to limit NIS influx to the region. This may be particularly relevant for future scenarios of increased vessel traffic and ocean warming, which are likely to interact to increase establishment success of invaders from the south.
KeywordsAnthropogenic transport Biofouling Introduced Latitudinal gradient Nonindigenous species Vector
This research was funded by the Alaska Department of Fish and Game (project leader Tammy Davis). Gary Freitag, Barbara Morgan, Steve Corporon, Monaca Noble, and Trevor Ruiz provided local assistance in Ketchikan, and we also thank Dr Ernie Meloche for inspiration in the field. Other parties who offered assistance in the form of data, access, local knowledge, or personnel include Allen and Saunya Alloway at Wind and Water Charters and Scuba, Alaska Forestry Service, Ketchikan Customs and Border Protection, and Ketchikan Ports and Harbors. Taxonomic experts were Kristen Larson (tunicates), Jeff Cordell (mobile crustacea), Chris Brown (barnacles), and Linda McCann (bryozoans). The genetic analyses were completed by Jonathon Geller’s laboratory.
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