Invasion
Invasion Description
1st record: Solano County/CA/Grizzly Bay (Carlton et al. 1990); CA/San Pablo Bay (1987, Carlton et al. 1990).
Geographic Extent
Solano County/CA/Grizzly Bay (Carlton et al. 1990); cargo ship 'Florikan'/CA/Suisun Bay (Llanso et al. 2011); CA/San Pablo Bay (1987, Carlton et al. 1990, numerically dominant in 1989, 1993, and 2000, Peterson et al. 2010); Point Sacramento/CA/Suisun Bay (1987, Carlton et al. 1990); Sacramento County/CA/Sherman Lake (1987, Cohen et al. 1990); Berkeley/CA/San Francisco Bay (1987, Carlton et al. 1990); Coyote Point/CA/South San Francisco Bay (1987, Carlton et al. 1990); Palo Alto/CA/South San Francisco Bay (1988, Carlton et al. 1990); CA/Steinberger Slough, South San Francisco Bay (1988, Carlton et al. 1990); CA/Plummer Creek, South San Francisco Bay (1988, Carlton et al. 1990); CA/Mowry Slough, South San Francisco Bay (1988, Carlton et al. 1990); CA/Coyote Creek, South San Francisco Bay (1988, Carlton 1990); China Camp/CA/San Pablo Bay (2005, Robinson et al. 2011); Petaluma Turning Basin/CA/Petaluma River (2004, Cohen et al. 2005); Fresh-Brackish (Delta, mean 0.7 PSU) to Marine Muddy, (South and Central bays, mean salinity 27.5 PSU, peak abundance at Main-Estuarine transition, mean salinity 16.1PSU, Lee et al. 2003))
Vectors
| Level | Vector |
|---|---|
| Probable | Ballast Water |
Regional Impacts
| Ecological Impact | Herbivory | |
| By 1988, Corbula amurensis had become a dominant filter-feeder in the San Francisco Bay benthic community (Carlton et al. 1990). Its huge biomass resulted in the disappearance of the summer phytoplankton maximum, which normally occurs in years of low river flow (Alpine and Cloern 1992; Jassby et al. 2002). | ||
| Ecological Impact | Competition | |
| The invasion of Corbula amurensis was accompanied by declines in the previously dominant, largely introduced, dry-season benthos, including Mya arenaria, Gemma gemma, Ampelisca abdita, Monocorophium acherusicum and Streblospio benedicti (Nichols et al. 1990; Poulton et al. 2004). | ||
| Ecological Impact | Predation | |
| The effects on the zooplankton include direct predation as copepod larvae (nauplii) are filtered out of the water (Kimmerer et al. 1994) as well as food deprivation. Predation on copepod nauplii and copepodites, together with decreases in phytoplankton abundance, have led to the decline of the formerly domonant copepod Eurytemora carolleeae (=E. affinis (Kimmerer and Lougee 2015). Grazing rates of C. amurensis on cilate microzooplankton also were significant, exceeding estimated growth rates, and potentially disrupting a link in the microbial food-web (Greene et al. 2011). Decreased recruitment of many species of fishes, including the economically important introduced Striped Bass (Morone saxatilis) and the endangered Delta Smelt (Hypomesus transpacificus) has been attributed, in part, to decreased food availability resulting from the huge filtering biomass of C. amurensis (Feyrer et al. 2003). | ||
| Ecological Impact | Trophic Cascade | |
| The Corbula amurensis invasion and suppression of phytoplankton biomass has had effects throughout the estuary's food-web, resulting in diminished food supplies for other benthic filter-feeders (Nichols et al. 1990), for filter-feeding zooplankton (Kimmerer et al. 1994), and for predators on benthos and zooplankton, such as fishes (Feyrer et al. 2003). Declines in zooplankton biomass resulting from reduced phytoplankton food and direct predation by clams on copepod nauplii have apparently contributed to sharp declines in mysids and fishes (Feyrer et al. 2003). Decreased recruitment of many species of fishes, including the economically important introduced Striped Bass (Morone saxatilis) and the endangered Delta Smelt (Hypomesus transpacificus) has been attributed, in part, to decreased food availability resulting from the huge filtering biomass of C. amurensis and its predatory impact on zooplankton.The development of the large Corbula biomass has also affected the overall flow of nutrients in the ecosystem, including C02, which is released in the process of shell formation (Chauvaud et al. 2003) and dissolved Si (silicon), which is taken up by diatoms, whose biomass has been greatly decreased by grazing (Kimmerer 2005). The invasion has resulted in a significant increase in carbon release by the estuary (Chauvaud et al. 2003) and a sharp decrease in silica uptake (Kimmerer 2005). The decreased diatom biomass in the estuary has also resulted in increased light penetration and a shift in production to other phytoplankton, such as flagellates and cyanobacteria, and to macrophytes (larger floating and submerged plants) such as Egeria densa (Brazilian Waterweed) and Eichornia crassipes (Water Hyacinth) (Jassby 2008). Since the invasion of C. amurensis, the peak of phytoplankton productivity has shifted to earlier in the year, shifting the peak of zooplankton abundance, resulting in a possible mismatch between the availability of prey and the larval period of the Delta Smelt (Merz et al. 2016). | ||
| Ecological Impact | Food/Prey | |
| Since its invasion, Corbula amurensis had become a major prey item for sturgeon and diving ducks, such as the Lesser Scaup (Athya affinis). Numbers of scaup aggregating in San Pablo and Suisun Bay increased following the invasion (Richman and Lovvorn 2004). During a period of colder water, in 1999-2004, the abundance of C. amurensis and other bivalves decreased, apparently as a result of an influx of cool-water predators, including shrimp (Crangon sp.), Dungeness Crabs (Metacarcinus magister) and English Sole (Parophrys vetulus) (Cloern et al. 2007). Corbula amurensis has become the dominant prey item of the White Sturgeon (Acipenser transmontanus), but the poorer food quality of the invading clams, and a reduction in benthic diversity, have led to a dietary shift including an increased consumpiton of fish (Zeug et al. 2014). | ||
| Ecological Impact | Toxic | |
| Corbula amurensis efficiently concentrates toxins, such as selenium, pesticides, etc., from the water column (Cohen 2005; Lee et al. 2006). While the invasion has resulted in increased aggregations of diving ducks, e.g. Lesser Scaup (Athya affinis), the toxin load from feeding on the clams may be contributing to decreasing success in breeding on the bird's nesting grounds (Richman and Lovvorn 2004). | ||
| Economic Impact | Fisheries | |
| Some recreationally and aesthetically important species, such as sturgeon (Cohen 2005) and diving ducks (Richman and Lovvorn 2004) may be benefiting from increased food supplies, but negative effects from concentrated toxins on the populations and human consumers will be more difficult to detect. Declines in many recreationally important fish stocks, such as Striped Bass (Morone saxatilis), as well as native endangered species, such as Delta Smelt (Hypomesus transpacificus) have been attributed, in part to the food-web changes (Feyrer et al. 2003), although these effects are difficult to separate from the many other human impacts on the inner Bay-Delta system. | ||
| Economic Impact | Aesthetic | |
| Filtering by the clams has resulted in increased water clarity in the Delta, probably with some aesthetic and recreational benefits. Some recreationally and aesthetically important species, such as sturgeon and diving ducks may be benefiting from increased food supplies, but negative effects from concentrated toxins on the populations and human consumers will be more difficult to detect. | ||
| Ecological Impact | Habitat Change | |
| Intense grazing of phytoplankton by Corbula amurenisis has affected the sediment by adding large quantities of pseudofeces, increasing the amount of suspended particles (Carlton et al. 1990). Grazing by C. amurenisis has decreased phytoplankton biomass, potentially increasing water clarity, and favoring submersed vegetation (Jassby 2008). Pseudofeces, bound by mucus, produced by Corbula, as well as the mucus produced by other native and introduced deposit feeding and tube-building benthos, contributes to a surface layer of flocculent fluff, which may trap much more phtyoplankton than that actually consumed by the animals (Jones et al. 2009). | ||