Invasion
Invasion Description
1st record: Blaine/WA/Semiahmoo Bay, Straits of Georgia (1991, Forsyth 1993, cited by Dudas 2005)
Geographic Extent
British Columbia/Smith Sound (approx. map location, 2006, Gillespie et al. 2007); Campbell River, Vancouver Island/British Columbia/Georgia Strait (2008, Choi et al. 2016); Vancouver Island/British Columbia/Baynes Sound (Lewis et al. 2007, 49.5°N, 124.8°W); Brooks Peninsula, Vancouver Island/British Columbia/Pacific Ocean (Dudas 2005); Nanaimo,/Vancouver Island/British Columbia/Georgia Strait (2008, Choi et al. 2016); Vancouver Island/British Columbia/Cowichan Bay (2008, Choi et al. 2016); Port Alberni, Vancouver IslandVancouver Island/Alberni Inlet (2008, Chi et al. 2016); British Columbia/Barkley Sound (1995, Mills 1998-2002; Dudas 2005); Blaine/WA/Semiahmoo Bay, Straits of Georgia (1991, Dudas 2005); Waldron Island/WA/Cowlitz Bay, Straits of Juan de Fuca (1993, Mills et al. 1998-2004); West Beach, Orcas Island/WA/Straits of Juan de Fuca (1993, Mills et al. 1998-2004); WA/Padilla Bay (1996, Mills 1998-2004; Riggs 2011); Port Ludlow Marina/WA/Puget Sound (1998, Cohen et al. 1998; Mills 1998-2004); Hood Head/WA/Hood Canal (1999, Mills 1998-2002); Seabeck/WA/Hood Canal (2004, Mills 1998-2004); Jefferson County/WA/Discovery Bay (1993, Mills 1998-2004); Jefferson County/WA/Sequim Bay (1993, Mills 1998-2004); Port Townsend/WA/Strait of Juan de Fuca (1998, Mills 1998-2004); WA/Neah Bay (1998, Mills 1998-2002); WA/Clallam Bay (1998, Mills et al. 1998-2004); Pillar Point/WA/Strait of Juan de Fuca (1998, Mills 1998-2004)
Vectors
| Level | Vector |
|---|---|
| Probable | Ballast Water |
Regional Impacts
| Economic Impact | Fisheries | |
| The fisheries potential of N. obscurata in British Columbia was examined by Gillespie et al. (1999). They are harvested by recreational clammers, and taken commercially in harvests of Venerupis philippinarum (Japanese Littlenecks, Manila Clams) (Carswell et al. 2006). Websites indicate that Varnish Clams are often sold as 'Savory Clams' and are well-regarded for their flavor. In Washington State, this clam was opened to recreational fisheries in 2004 (Meacham 2004). | ||
| Ecological Impact | Food/Prey | |
| In Bayne Sound, Vancouver Island, British Columbia, Purple Varnish Clams (Nuttallia obscurata) and Japanese Littleneck Clams (Venerupis philipinarum) were the primary food items of the wintering diving duck species Melanitta perspicillata (Surf Scoter) and M. fusca (White-Winged Scoter) and appeared to be preferred over the native Macoma spp. (Lewis et al. 2007). It is not clear whether the exotic clams have altered the distribution or abundance of these migratory ducks. At low tide, Varnish Clams are eaten by shorebirds, including Black Oystercatchers (Haematopus bachmanni), Glaucous-Winged Gulls (Larus glaucescens) and Northwestern Crows (Corvus caurinus) (Gillespie et al. 1999). Experiments indicate that N. obscurata is very vulnerable to predation by crabs (Cancer productus, Red Rock Crabs and Metacarcinus magister, Dungeness Crabs) (Byers 2005; Dudas et al. 2006), but its not clear whether the clam invasion has had any effect on crab populations. | ||
| Economic Impact | Health | |
| As with other native and introduced bivalves, red-tide blooms of toxic dinoflagellates can cause Varnish Clams to accumulate toxins that can cause Paralytic Shellfish Poisoning (PSP). Nuttallia obscurata is a facultative deposit feeder, and is likely to encounter dinoflagellate cysts in sediments. Since it often occurs in estuarine habitats, it has the potential to accumulate other toxins from polluted sediments, including heavy metals and fecal bacteria (Gillespie et al. 1999; Meacham 2004). | ||
| Ecological Impact | Habitat Change | |
| In experiments on Denman Island, in the Strait of Georgia, British Columbia, high densities of varnish clams increased ammonium concentrations, and changed the particle composition by increasing the content of fine sand and silt. The increaed ammonium and silt in the sediments could contribute to phyplankton blooms and turbidity (Chan and Bendell 2013). | ||