Invasion
Invasion Description
1st Record: CA/San Francisco Bay (1893, in the crop of a duck in the San Francisco Market, Carlton 1979)
Geographic Extent
CA/Elkhorn Slough (1965, Carlton 1992); South Marsh Trail/CA/Elkhorn Slough (Wasson et al. 2001); Kirby Park/CA/Elkhorn Slough (Wasson et al. 2001); Hudson's Landing/CA/Elkhorn Slough (Wasson et al. 2001); 'east Bay shore'/CA/San Francisco Bay (Stearns 1899, cited by Carlton 1979); CA/San Pablo Bay (Nichols and Thompson 1985; Hopkins 1986); CA/Carquinez Strait-Suisun Bay (Hopkins 1986); CA/South San Francisco Bay (Nichols and Thompson 1985); Coyote Point Marina/CA/South San Francisco Bay (Cohen et al. 2005); Main Estuarine (Suisun-San Pablo, mean 16.1 PSU) to Marine Muddy, (South and Central bays, mean salinity 27.5 PSU, peak abundance at Estuarine-Margin, San Pablo, mean salinity 22.8 PSU, Lee et al. 2003); CA/Bolinas Lagoon (1918, Cohen and Carlton 1995); CA/Tomales Bay (1965, Johnson and Juskevice 1965, cited by Carlton 1979); CA/Bodega Harbor (1974, Standing 1975, cited by Carlton 1979)
Vectors
| Level | Vector |
|---|---|
| Probable | Oyster Accidental |
Regional Impacts
| Ecological Impact | Competition | |
| In San Francisco and Tomales Bays, competition was suspected with Nutricola tantilla (=Transennella tantilla). The two species were rarely found together in the same samples (Narchi 1971; Carlton 1979). In Bodega Harbor, G. gemma was rare, until the arrival of the invasive Green Crab (Carcinus maenas), which preferred the larger Nutricola spp. In experiments, Gemma grew slowly in the presence of abundant Nutricola, but grew and reproduced much faster when Nutricola was rare (Grosholz 2005). | ||
| Ecological Impact | Food/Prey | |
| Gemma gemma comprised 55% of food items of the shorebirds Avocet (Recurvirostra americana and Red Knot (Calidris canutus) surveyed in Palo Alto, San Francisco Bay (Recher 1963). | ||