The shape of this oyster is quite variable. The species was introduced from Japan in the early 1900's (to Washington and British Columbia in 1922) and is the most important aquacultured species on the US West Coast. The japanese littleneck clam Tapes japonica
and the Japanese oyster drill Ceratostoma inornatum
, as well as the intestinal parasitic copepod Mytilicola orientalis
were apparently introduced to our coast along with this species. May live 20 years or more. Often contains irregular, non-lustrous pearls. Predators include predatory oyster drill snails, the crabs Cancer magister, Cancer productus, Cancer oregonensis, Hemigrapsus nudus, and H. oregonensis
, some sea stars, and the black oystercatcher (bird). The blue mud shrimp Upogebia pugettensis
digs sediment from its burrows and smother the oysters with sediment. Attaches to hard substrates, such as the shells of other oysters. The oysters are imported as very small individuals (spat) and raised in commercial oyster beds. They are said to poorly reproduce in California, so are found only in the oyster beds. I have seen many oysters in apparently natural conditions here in Washington, so they must be able to reproduce at least a bit better here. Sexes are separate in this species, but an individual may change sexes in the winter and may alternate being male and female. A few are simultaneous hermaphrodites. They outgrow native oysters, probably partly because they are more efficient finter feeders, and can feed on nannoplankton, which native oysters cannot do. Occasionally they are influenced by a red tide (usually by the dinoflagellate Gonyaulax catanella
) and become toxic to eat.