Crassostrea gigas (Thunberg, 1793)
Common name(s): Japanese oyster, Pacific oyster, Giant Pacific oyster, Miyagi oyster
|Synonyms: Ostrea gigas|
|Crassostrea gigas from Padilla Bay. Scale is inches.|
|(Photo by: Dave Cowles, July 2005)|
How to Distinguish from Similar Species: This is the largest local oyster; and usually the most commonly encountered one. The other introduced oyster (Crassostrea virginica) and the Olympic oyster (Ostrea lurida) do not have the conspicuous frills on the valves and grow to no larger than 15 cm high.
Geographical Range: Widely introduced on the west coast from Japan. Prince William Sound, AK to Newport Bay, CA. Very common in Willapa Bay, and in Departure Bay and the Georgia Strait in British Columbia.
Depth Range: Intertidal to 6m
Habitat: Firm sediment or rocky beaches
Biology/Natural History: 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.
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Brusca and Brusca, 1978
McConnaughey and McConnaughey, 1985
Morris et al., 1980
Ricketts et al., 1985