The Asian or Chinese clam is a small mollusc (2 - 3cm) that can survive in freshwater and saltwater which is unusual for this type of mollusc. They live partly buried in the sediment, with their hind third or half exposed above the surface. They are found living on mud, sand, peat and clay substrates mostly in the subtidal zone.
Where did they come from?
They are native to Southern Siberia south of about 53° N latitude, Japan, Korea and China to about 22° N latitude.
Where are they found in Australia?
This is one dangerous species which is not yet present in Australia, but could be introduced at any time. They have been introduced into California, where large populations have become established in San Francisco Bay and are having a significant impact on the aquatic environment.
How was it introduced?
It was probably introduced to San Francisco Bay as larvae in the ballast of cargo ships.
What is its impact?
First found in San Francisco Bay in 1986, the Chinese clam took only two years to spread throughout the bay estuary, irrespective of the sediment type, water depth or salinity. It quickly reached densities of greater than 10,000 individuals per square metre. Within one year the composition of the soft substrate community had changed dramatically, with P. amurensis comprising more than 95 per cent of its biomass.
This single species forms a carpet over the floor of San Francisco Bay and estuary, displacing the former benthic community and causing sediment disturbance.
The Chinese clam is a suspension feeder and has been found to consume large quantities of phytoplankton. This has resulted in a change in the phytoplankton dynamics in San Francisco Bay and has been blamed for the collapse of some fisheries in the area.
How is it controlled?
Chinese clams predators are birds, fish and crabs. However, options for its large-scale control are limited.