Corbicula fluminea is a small (<50 mm) lightly-colored bivalve with shell ornamented by distinct, concentric ridges. Dark shell morphs exist but are limited to the southwestern United States. The shells of the yellow morphs are straw yellow on the outside and white on the inside; those of brown morphs were dark brown and purple, respectively.
Ecological Threat: Not much is known about the Asian clam or the possible threat of disrupting native ecosystems. It has been documented, however, that indigenous fish and crayfish have added this clam to their diets. While this may seem to be a positive solution, the clam could potentially be a vector for exotic parasites or diseases that could then infect native species.
In terms of economic importance, the Asian clam, Corbicula fluminea, is mostly known as a biofouler of many electrical and nuclear power plants across the country. As water is drawn from rivers, streams and reservoirs for cooling purposes so are Corbicula larvae. Once inside the plant, this mussel can clog condenser tubes, raw service water pipes, and fire fighting equipment. Economic problems can result from the decreased efficiency of energy generation. Warm water effluents at these power plants make a hospitable environment for stabilizing populations.
Biology: Unlike most of the other invasive species in the US, the Asian clam is not able to rapidly distribute itself. That is, the clam has become widely distributed by relying upon humans as an agent of dispersal. Scientists remain unsure about what barriers may act upon natural distributive efforts by these clams. Therefore, it is difficult to predict the range of the clam in the future.
The clam reproduces rapidly and is tolerant to cold waters adding to its success as an invasive species. Asian clams can self-fertilize, and release up to 2,000 juveniles per day, and more than 100,000 in a lifetime. Juveniles are only 1 mm long when discharged, and take one to four years to reach maturity. The life span is between one to seven years.
History: The first collection of C. fluminea in the United States occurred in 1938 along the banks of the Columbia River near Knappton, Washington. Since this first introduction, it is now found in 38 states and the District of Columbia. C. fluminea was thought to enter the United States as a food item used by Chinese immigrants. It may have come in with the importation of the Giant Pacific oyster (also from Asia). The mechanism for dispersal within North America is unknown. Since man is suspected to be the primary agent of dispersal, no large-scale geographic features function as dispersal barriers. Current methods of introduction include bait bucket introductions, accidental introductions associated with imported aquaculture species, and intentional introductions by people who buy them as a food item in markets. The only other significant dispersal agent is thought to be passive movement via water currents. Fish and birds are not considered to be significant distribution vectors.
U.S. Habitat: A freshwater clam that prefers cooler waters.
Native Origin: Eurasia
U.S. Present: Currently found up and down both coasts and also occurs in most of the heartland. Only parts of the Dakotas, Montana, and Alaska appear to not contain the Asian clam.
Distribution in Texas: Currently found in the following Riverways: Angelina, Colorado, Rio Grande, Guadalupe, San Antonio, San Jacinto, Sabine, Red, White, and Brazos drainages; the Clear and West Forks of the Trinity River.
Currently, many organizations are struggling to find a way to prevent the spread of Asian clams. Due to their current ubiquity, that task has proved difficult. Many states are installing screens over intake pipes to power plants or man-made lakes in hopes to prevent the larvae from entering their waterways.
Nichols, Frederic, Janet Thompson, and Laurence Schemel. 1991. Remarkable invasion of San Francisco Bay (California, USA) by the Asian clam Potamocorbula amurensis. II. Displacement of a former community. Marine Ecology Press Series. 65.95: 95-101. Web, accessed 7 Sep. 2011, http://www.calwater.ca.gov.
Nichols, S. J., and M. G. Black. 1994. Identification of larvae: the zebra mussel (Dreissena polymorpha), quagga mussel (Dreissena rosteriformis bugensis), and Asian clam (Corbicula fluminea). Canadian Journal of Zoology. 72.3: 406-417. Web, accessed 7 Sep. 2011, http://www.nrcresearchpress.com.
Sousa, R., C. Antunes, and L. Guilhermino. 2008. Ecology of the invasive Asian clam Corbicula fluminea (Müller, 1774) in aquatic ecosystems: an overview." International Journal of Limnology. 44.2: 85-94. Web, accessed 7 Sep. 2011, http://journals.cambridge.org.