Species Regional Summary
Potamocorbula amurensis
San Francisco Bay ( P090 )

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).

References

Alpine, A. E., Cloern, J. E. (1992) Trophic interactions and direct physical effects control phytoplankton biomass and production in an estuary, Limnology and Oceanography 37(5): 946-955

Barnett, Rachel; Bell, Sabrina; Floerke, Wyatt; Templin, Bill (2011) <missing title>, California Interagency Ecological Program, Sacramento CA. Pp. 13

Carlton, James T.; Thompson, Janet K.; Schemel, Laurence E.; Nichols, Frederic H. (1990) Remarkable invasion of San Francisco Bay (California, USA) by the Asian clam Potamocorbula amurensis. I. Introduction and dispersal, Marine Ecology Progress Series 66: 81-94

Cloern, James E.; Jassby, Alan D.;Thompson, Janet K.; Hieb, Kathryn A. (2007) A cold phase of the East Pacific triggers new phytoplankton blooms in San Francisco Bay, Proceedings of the National Academy of Sciences 104(47): 18561-18565

Feyrer, Frederick; Herbold, Bruce; Matern, Scott A.; Moyle, Peter (2003) Dietary shifts in a stressed fish assemblage: consequences of a bivalve invasion in the San Francisco estuary., Environmental Biology of Fishes 67: 277-288

Greene, Valerie E.; Sullivan, Lindsay J.; Thompson, Janet K.; Kimmerer, Wim J. (2011) Grazing impact of the invasive clam Corbula amurensis on the microplankton assemblage of the northern San Francisco Estuary, Marine Ecology Progress Series 431: 183-193

Jones, Nicole L.; Thompson, Janet K.; Arrigo, Kevin R.; Monismith, Stephen G. (2009) Hydrodynamic control of phytoplankton loss to the benthos in an estuarine environment, Limnology and Oceanography 54(3): 952-969

Kim, Daemin; Taylor, Andrew T.; Near, Thomas J. (2022) Phylogenomics and species delimitation of the economically important Black Basses (Micropterus), Scientific Reports 12(9113): Published online
https://doi.org/10.1038/s41598-022-11743-2

Kimmerer, William; Gartside, Ellen; Orsi, James J. (1994) Predation by an introduced clam as the likely cause of substantial declines in zooplankton of San Francisco Bay., Marine Ecology Progress Series 113: 81-93

Kimmerer, Wim J.; Lougee, Laurence (2015) Bivalve grazing causes substantial mortality to an estuarine copepod population, Journal of Experimental Marine Biology and Ecology 473: 53-63

Lee, Byeong-Gweon; Lee, Jung-Suk; Luoma, Samuel N. (2006) Comparison of selenium bioaccumulation in the clams Corbicula fluminea and Potamocorbula amurensis: a bioenergetic modeling approach, Environmental Toxicology and Chemistry 25(7): 1933-1940

Llansó, Roberto J.; Sillett, Kristine; Scott, Lisa (2011) <missing title>, Versar, Inc., Columbia MD. Pp. <missing location>

MacNally, Ralph, and 10 authors (2010) Analysis of pelagic species decline in the upper San Francisco Estuary using multivariate autoregressive modeling (MAR), Ecological Applications 20(5): 1417-1430

Mathieson, Arthur C.; Dawes, Clinton J. (2017) Seaweeds of the Northwest Atlantic, University of Massachusetts Press, Amherst MA. Pp. <missing location>

Nichols, Frederic H.; Thompson, Janet K.; Schemel, Laurence (1990) Remarkable invasion of San Francisco Bay by the Asian clam Potamocorbula amurensis. II. Displacement of a former community., Marine Ecology Progress Series 66: 95-101

Poulton, V.K.; Lovvorn, J.R.; Takekawa, J.Y. (2004) Spatial and overwinter changes in clam populations of San Pablo Bay, a semiarid estuary with highly variable freshwater inflow., Estuarine, Coastal and Shelf Science 59: 459-473

Powell, N. A. (1970) Indo-Pacific Bryozoa new to the Mediterranean, Israel Journal of Zoology 18: 157-168

Richman, Samantha E.; Lovvorn, James R. (2004) Relative foraging value to lesser scaup ducks of native and exotic clams from San Francisco Bay., Ecological Applications 14(4): 1217-1231

Robertson, D. Ross; Dominguez-Dominguez, Omar; Solís-Guzmán; María Gloria; Kingon, Kelly C (2021) Origins of isolated populations of an Indo-Pacific damselfish at opposite ends of the Greater Caribbean, Aquatic Invasions 16: 269-280

Robinson, April; Cohen, Andrew N.; Lindsey, Brie; Grenier, Letitia (2011) Distribution of macroinvertebrates across a tidal gradient, Marin County, California, San Francisco Estuary and Watershed Science 9(3): published online

2014-2022 California Fish Website. Web database



Winder, Monika; Jassby, Alan D. (2011) Shifts in zooplankton community structure: implications for food web processes in the upper San Francisco estuary, Estuaries and Coasts 34: 675-690

Winder; Monika; Jassby, Alan D.; Mac Nally, Ralph (2011) Synergies between climate anomalies and hydrological modifications facilitate estuarine biotic invasions, Ecology Letters 14: 749-757

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