What are they?
Corbula amurensis, commonly known as the overbite clam, Asian marine clam or Amur River clam, is a tan, white or yellow clam, up to about 25 mm long. It lives partly buried in the sediment, with its hind third or half exposed above the surface. The right half of the shell is a bit larger than the left and slightly "overbites" it at the lower margin, which distinguishes Corbula amurensis from similar-looking clams on the Pacific Coast.
Are they here yet?
No, but they are present in San Fransisco Bay. The first record of Corbula amurensis in North America was three specimens dredged from the bottom of San Francisco Bay in October 1986. By 1987, Corbula had become the most abundant benthic organism in the northern part of the Bay, carpeting the bottom at densities of over 16,000 juvenile clams per square meter. Corbula amurensis most likely arrived in San Francisco Bay as larvae discharged from a ship's ballast tank.
Why should I care?
Corbula amurensis grows prolifically, forming dense quantities very rapidly and displacing other native species. They also consume large amounts of plankton, a major food source for critical fish species – such as the delta smelt – and other aquatic organisms, by sucking in and filtering plankton from the water. The larger the geographic distribution of the clam, the more widespread its effects on the aquatic food web.
What should I do if I find one?Report a sighting
How can we stop them?To prevent spread, clean, drain, and dry your equipment after each use.
What are their characteristics?
- Corbula amurensis is a tan, white or yellow clam, up to about 25 mm long.
- The 'overbite' clam, derives its name from right half of the shell being larger than the left and slightly overbiting its lower margin.
- The shell has the overall shape of a broad isosceles triangle.
- In younger clams the shell surface is covered by a thin, smooth tissue, but in older clams the tissue becomes wrinkled around the lower margin.
- Corbula amurensis is primarily subtidal, but is occasionally abundant on intertidal mudflats.