Invasion
Invasion Description
1st record: Redwood City/CA/Redwood Shores Lagoon (1990, Cohen et al. 1995); Sonoma County/CA/Estero Americano (1989, one specimen, unknown establishment, Grosholz and Ruiz 1995)
Geographic Extent
Sonoma County/CA/Estero Americano (1989, one specimen, unknown establishment, Grosholz and Ruiz 1995); CA/Bodega Harbor (1993, introduced, established, Grosholz and Ruiz 1995); CA/Walker Creek, Tomales Bay (1993, introduced, established, Grosholz and Ruiz 1995); Drakes Estero/CA/Pacific Ocean (1993, Groshoz and Ruiz 1995); CA/Bolinas Lagoon (1993, introduced, established, Grosholz and Ruiz 1995); Stinson Beach/CA/Seadrift Lagoon (Fimrite 2017).; Redwood City/CA/Redwood Shores Lagoon; San Mateo County/CA/Redwood Creek (South Bay); San Mateo County/CA/Belmont Slough (1992, Cohen et al. 1995); Hayward/CA/San Francisco Bay (1992, Cohen et al. 1995); San Mateo County/CA/Foster City Lagoon (1992, Cohen et al. 1995); Crab Cove, Crown Beach, and Bay Farm Island/CA/San Francisco Bay (1999, Cohen et al. 1995); Coyote Point/CA/San Francisco Bay (1992, Cohen et al. 1995); Berkeley Aquatic Park/CA/San Francisco Bay (1992, Cohen et al. 1995); Marin Co./CA/Loch Lomond Harbor (1992, Cohen et al. 1995); Dumbarton Bridge/CA/South Bay (1992, Cohen et al. 1995); CA/San Pablo Bay (1993, Cohen et al. 1995); China Camp/CA/San Pablo Bay (2005, Robinson et al. 2011); Point Pinole/CA/San Pablo Bay (1993, Cohen et al. 1995); Berkeley Marina/CA/San Francisco Bay (1994, Cohen et al. 1995); Benicia/CA/Carquinez Strait (1994, Cohen et al. 1995); Black Point/CA/San Pablo Bay (1993, Cohen et al. 1995); CA/Elkhorn Slough (Monterey Bay) (1993, introduced, established, Grosholz and Ruiz 1995; Wasson 2001); San Luis Obispo County/CA/Morro Bay (1998, introduced, establishment unknown, Grosholz, unpublished; USGS Nonindigenous Aquatic Species Program 2009)
Vectors
| Level | Vector |
|---|---|
| Probable | Discarded Bait |
| Alternate | Ballast Water |
| Alternate | Fisheries Accidental (not Oyster) |
Regional Impacts
| Ecological Impact | Predation | |
| In Bodega Harbor CA, abundances of the clams Nutricola tantilla and N. confusa and the native crab Hemigrapsus oregonensis were sharply reduced after the invasion of Carcinus maenas. Experiments indicated high rates of feeding on the native clams and crabs (Grosholz et al. 2000). Over an 11-year period in Bodega Harbor, H. oregonensis abundance was negatively correlated with C. maenas abundance, but recovered, with a lag period, when C. maenas declined. However, C. maenas predation had persisting effects on the size and intertidal distribution of H. oregonensis (de Rivera et al. 2011). In Tomales Bay, Carcinus maenas is a less effective predator than the native crab (Cancer antennarius), on native (Acanthinucella spirata) and introduced whelks (Urosalpinx cinerea, Atlantic Oyster Drill), resulting in an increased abundance and habitat range of whelks in the inner Bay, where C. maenas better tolerates low salinities (Kimbro et al. 2009). | ||
| Ecological Impact | Competition | |
| In laboratory experiments, Carcinus maenas spent more time around bivalve bait than the native crab Hemigrapsus oregonensis, and was more successful at approaching competitors surrounding the bait than H. oregonensis, in Bodega Bay Harbor CA (Jensen et al. 2002). Carcinus maenas also displaces Metacarcinus magister (Dungeness Crabs) of equal size in feeding trials, and causes M. magister to emigrate from shelters in laboratory trials (McDonald et al. 2001). In enclosure experiments, Green Crabs reduced the abundance and quality of food available for wintering shorebirds (Dunlin, Calidris alpina) (Estelle and Grosholz 2012). | ||
| Ecological Impact | Trophic Cascade | |
| After the Carcinus maenas invasion in Bodega Bay Harbor, California, several invertebrate species, the polychaetes Exogene sp. and Lumbrinereis sp. and the tanaid Leptochelia dubia increased in abundance, probably as an indirect effect of reduction in Nutricola spp. populations (Grosholz et al. 2000). The introduced clam Gemma gemma increased dramatically (two orders of magnitude) after the Carcinus invasion, apparently because of decreased competition from native Nutricola clams (Grosholz 2005). In Tomales Bay, Carcinus maenas is a less effective predator than the native crab, Cancer antennarius, on native (Acanthinucella spirata) and introduced whelks (Urosalpinx cinerea, Atlantic Oyster Drill), resulting in an increased abundance and habitat range of whelks in the inner Bay, where C. maenas better tolerates low salinities (Kimbro et al. 2009). The increased abundance of U. cinerea, also more tolerant of low salinity than native whelks, has resulted in increased mortality and a near-absence of the native Olympia Oyster (Ostrea lurida). | ||
| Economic Impact | Fisheries | |
| In Bodega Bay, Caliornia, Manila Clams (Venerupis philippinarum) planted in mesh bags, were prone to heavy predation by Carcinus maenas. Predation was reduced by planting the clams later in the season, when the clams were larger (Grosholz et al. 2001). Estimated current losses of bivalve fisheries (Pacific Littleneck, Japanese Littleneck, Softshell Clam, Blue Mussel) in California are negligable, but with future population increases of C. maenas, could reach $20,000-60,000 per year (Grosholz et al. 2011). | ||