Northern Range Expansion and Coastal Occurrences Northern Range Expansion and Coastal Occurrences of the New Zealand Mud Snail Potamopyrgus of the New Zealand Mud Snail Potamopyrgus Antipodarum (Gray, 1843) in the Northeast Pacific Antipodarum (Gray, 1843) in the Northeast Pacific

The New Zealand mud snail Potamopyrgus antipodarum (Gray, 1843) is a common invasive species in fresh and brackish water ecosystems in Europe, Australia, Japan, and North America. In some invaded habitats, P. antipodarum can reach high densities (over 500,000 snails m -2 ) and dominate the biomass of the benthos, leading to detrimental impacts to native biota and changes in ecosystem dynamics. We report the previously unpublished occurrence of P. antipodarum in thirteen fresh and brackish water systems adjacent to the Pacific coast of North America including a new northern range for P. antipodarum : Port Alberni, Vancouver Island, British Columbia, Canada (49.2479º, -124.8395º). We hypothesize the snail was spread from the Columbia River Estuary to Port Alberni via recreational watercraft or infected fishing equipment. Its discovery in Port Alberni reveals the potential for other aquatic nuisance species in the lower Columbia River to spread to British Columbia. Resource managers on the Pacific coast should remain vigilant and educate the public to prevent the further spread of the P. antipodarum as well as other aquatic invaders.

The New Zealand mud snail Potamopyrgus antipodarum (Gray, 1843) is a global invader present in several continents including Europe (Bondesen and Kaiser 1949), Tasmania and mainland Australia (Ponder 1988), Asia (Shimada and Urabe 2003) and North America (Bowler 1991).The hydrobiid snail is native to New Zealand and is distinguishable from other snails by the presence of an operculum, 5-6 body whorls often harboring a weak keel or carina and brooded young (Winterbourn 1970).They are very small (5-6mm in length) and may be found subtidally or intertidally on or under rocks and debris in fresh or brackish waters.Potamopyrgus antipodarum can be spread anthropogenically through movement of gear such as waders, boots, angling equipment, and boats or by the translocation of aquaculture materials (live fish or eggs; Bowler 1991;Haynes et al. 1985;Hosea and Finlayson 2005).Secondary introductions may occur on birds that carry the snails among their feathers or by fish that consume but are unable to digest snails (Bondesen and Kaiser 1949;Haynes et al. 1985).
In some invaded freshwater systems, P. antipodarum has become the most prevalent and numerically abundant species (Ponder 1988;Hall et al. 2006) reaching densities over 500,000 snails m -2 in vegetative and muddy substrates, and constituting between 65-92% of total invertebrate productivity (Hall et al. 2006).These herbivorous and detritivorous snails can also dominate carbon and nitrogen fluxes (Hall et al. 2003).The high densities achieved by P. antipodarum in invaded systems suggest that it may compete with native species for resources (Brown et al. 2008).However, the field evidence for a negative competitive effect is mixed, with some negative (Kerans et al. 2005), nonsignificant (Cada 2004) and positive (Schreiber 2002) correlations between densities of P. antipodarum and native fauna.Potamopyrgus antipodarum may also reduce the colonization rate of some macroinvertebrates (Kerans et al. 2005) and affect the survivorship of fish that consume them (Vinson and Baker 2008).The interactions with different trophic levels coupled with the high densities observed in many systems may lead to substantial changes in trophic dynamics and nutrient cycling in aquatic ecosystems (Bronmark 1989;Hall et al. 2003;Hall et al. 2006).
While P. antipodarum is usually described as a freshwater invader in North America, this species is being increasingly found in brackish estuarine environments and adjacent aquatic habitats (Bersine et al. 2008).We report occurrences of this invasive snail from a series of qualitative surveys and verified sightings in coastal aquatic systems of the northeast Pacific.Our surveys revealed several new invasions of brackish and freshwater environments by P. antipodarum including a new northern limit on the northeast Pacific coast for the invasive mud snail.Potamopyrgus antipodarum was discovered in Port Alberni Inlet (5 salinity), Vancouver Island, British Columbia during surveys conducted in July 2007.The snails occur in low densities amongst intertidal woody debris in areas adjacent (<1 km) to the primary marina and boat ramp for the town of Port Alberni.We also report twelve occurrences in the brackish and fresh water environments of Oregon and Washington, USA (Figure 1, Annex 1).We hypothesize that the well-established population of P. antipodarum in the Columbia River Estuary is the source of the snails found in Port Alberni.This hypothesis is supported by four main lines of evidence.1) P. antipodarum occurs in very high densities (over 200,000 snails/m 2 ; Litton 2000) in the Columbia River Estuary and has been there at least since 1996 (Bersine et al. 2008).2) The lower Columbia River Estuary hosts many recreational sport fisheries and boaters, which are likely vectors for P. antipodarum (Bowler 1991;Haynes et al. 1985;Hosea and Finlayson 2005).3) Port Alberni is also a popular destination for recreational fishers and boaters (G.Gillespie, per.obs.).4) P. antipodarum is highly tolerant to desiccation and can survive over 50 days on a wet substrate (Winterbourn 1970).Despite the large separation in physical distance between Port Alberni and the Columbia River Estuary (driving distance: 565 km, 9 hours driving), P. antipodarum could survive the transit in damp fishing gear, boating equipment, or on vegetation and mud attached to the hulls of boats and trailers.It is unlikely these snails were introduced to Port Alberni from the populations in Long Beach, Washington or other Oregon sites since many of these sites harbor lower densities of P. antipodarum (unpublished data) and are utilized by fewer recreational fishers and boaters compared to the Columbia River Estuary.The invasion of the Columbia River Estuary by P. antipodarum is thought to be a secondary introduction from the interior of the western USA since both populations exhibit the same clonal lineage (Dybdahl and Kane 2005).Thus, genetic analysis of the Port Alberni populations would reveal if this population is a new clone (new invasion from New Zealand or Australia) or of the same clonal lineage (secondary introduction).Potamopyrgus antipodarum could also invade locations north of Port Alberni.Using Genetic Algorithm for Rule-set Production (GARP), Loo et al. (2007) predicted P. antipodarum might be distributed in areas many kilometers north of Port Alberni due to its wide range of temperature and salinity tolerance.
The discovery of P. antipodarum in Port Alberni reveals the potential for further invasions of the numerous other non-native aquatic species present in the lower Columbia River, if this new population is sourced from there.The lower Columbia River receives a large volume of international and regional ship traffic and hosts over 54 non-native species (Sytsma et al. 2004) including several that could be transported similarly and can drastically alter aquatic habitats (e.g.Eurasian watermilfoil Myriophyllum spicatum [Linnaeus, 1753] and common reed Phragmites australis [Cav.]Trin.ex Steud).Thus, it is important to recognize the role of intraregional traffic (such as recreational boaters) in spreading invasive species initially introduced through commercial shipping (Wasson et al. 2001).This invasion also elucidates the importance of international cooperation in preventing and reporting the spread of aquatic invaders across international borders.
Due to their small size, resistance to desiccation, and parthenogenetic reproduction, there appear to be few (if any) feasible options in controlling P. antipodarum populations once they become established (New Zealand Mudsnail Management and Control Plan Working Group 2007).Resource managers, however, are employing several options to prevent the future spread of P. antipodarum such as posting signs at boat ramps, distributing informational media (pamphlets, brochures, websites; pers.obs.), and by establishing permanent and mobile washing stations at boat ramps (New Zealand Mudsnail Management and Control Plan Working Group 2007).Another option is to treat infected equipment.Richards et al. ( 2004) recommended two options to prevent the spread of P. antipodarum through infected equipment: 1) freezing for several hours or 2) drying infected equipment at 30ºC for at least 24 hours or at 40ºC for 2 hours.There are also several chemical options to decontaminate infected equipment including copper sulfate (252 mg/L Cu), Formula 409® Disinfectant (50% dilution), and benzethonium chloride compounds (1,940 mg/L; Hosea and Finlayson 2005).These types of chemical treatments only require five minutes of submergence to be effective and do not appear to damage neoprene and rubber wading gear, although care must be taken to dispose of those chemicals properly (Hosea and Finlayson 2005).While chemical options are effective in preventing the spread of P. antipodarum, knowledge of infested sites coupled with rigorous gear cleaning (scrubbing, draining, and drying) at these sites and elsewhere are cost effective means of limiting further transport of P. antipodarum and other aquatic invasive species.We urge resource managers to remain vigilant and aware of the threat P. antipodarum may hold for aquatic systems and to educate the public in order to prevent the further spread of P. antipodarum on the Pacific coast of North America.
supported by the US Fish and Wildlife Service Western Regional Panel on Aquatic Nuisance Species and Fisheries and Oceans Canada through their Aquatic Invasive Species Program.

Figure 1 .
Figure 1.Occurrences of Potamopyrgus antipodarum (▲) in aquatic systems of the coastal region of the northeast Pacific.The year of discovery is noted.BC= British Columbia (Canada), WA = Washington (USA), OR = Oregon (USA) Lake PS and Quinn GP (2002)Facilitation of native stream fauna by an invading species?Experimental investigations of the interaction of the snail, Potamopyrgus antipodarum (Hydrobiidae) with native benthic fauna.Biological Invasions 4: 317-325 Shimada K and Urabe M (2003) Comparative ecology of the alien freshwater snail Potamopyrgus antipodarum and the indigenous snail Semisulcospira spp.Venus 62: 39-53 Sytsma MD, Cordell JR, Chapman JW and Draheim RC (2004) Lower Columbia River aquatic nonindigenous species survey 2001-2004.Final technical report.Prepared for the United States Coast Guard and United States Fish and Wildlife Service Vinson MR and Baker MA (2008) Poor growth of Rainbow Trout fed New Zealand mud snails Potamopyrgus antipodarum.North American Journal of Fisheries Management 28: 701-709 Wasson K, Zabin CJ, Bedinger L, Diaz MC and Pearse JS (2001) Biological invasions of estuaries without international shipping: the importance of intraregional transport.Biological Conservation 102: 143-153 Winterbourn MJ (1970) The New Zealand species of Potamopyrgus (Gastropoda: Hydrobiidae).Malacologia 10: 283-321