Asian Clam
(Potamocorbula amurensis)

Description: The shells of the Asian clam are unequal in size giving this species a slight "overbite" that sets it apart from similar native species. This small clam only reaches a length of 2 to 3 cm. The exterior of the shell is sculptured with light concentric rings and yet can have a fairly smooth surface. The color of the shell can vary from white, tan, or yellow. It typically buries one-half to three-fourths of its body into the sediment and anchors itself with byssal threads from within the shell. The exposed portion of the clam is very often fouled with other organisms, differing from the clean shells of native clams that are entirely buried. Asian clams are often found in dense aggregations.

Habitat: This species is generally found living in mud, sand, and clay substrates in the intertidal or subtidal zone of bays and estuaries.

Origin: China, Japan, and Korea.

Invaded Areas: San Francisco Bay.

Concerns: The Asian clam is a very resilient invader capable of exploiting waters ranging greatly in salinity, temperature, and pollution levels. During the late 1980s, a population became established in the San Francisco Bay. In northern parts of the Bay, it has come to dominate benthic habitats, at densities of up to 2,000 individuals per square meter (or approximately 750 clams in an area the size of the page you are reading!). With densities of this magnitude, Asian clams have altered the flow of energy across estuarine food webs, clearing the water of phytoplankton and zooplankton, as well as displacing native benthic species. By consuming the planktonic food resources upon which juvenile fish rely, Asian clams could also have dramatic economic effects on fisheries.