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Pacific Cupped Oyster

Crassostrea gigas (Thunberg 1793)

Brief Summary

provided by Ecomare
You see more and more Pacific oysters in the Wadden Sea, Oosterschelde and Grevelingen. Although they are very tasty, not everyone is happy with the presence of this oyster. You can easily cut yourself on these razor-sharp shells. And there are places where they grow in such great numbers, they drive away other shellfish. Other benthic animals use these oysters as a safe hideaway and a sturdy underground. Although many birds have difficulties opening up their shells, there a number of bird species learning to conquer them.
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Diagnostic Description

provided by FAO species catalogs
Shell solid, inequivalve, extremely rough, extensively fluted, and laminated; left (lower) valve deeply cupped, its sides sometimes almost vertical, the right (upper) valve flat or slightly convex sitting withing left; inequilateral, beaks and umbones often overgrown; tending to be oblong in outline but often disorted and very irregular. The shape of the shell varies with the environment.

Colour usually whitish with many purple streaks and spots radiating away from the umbo. The interior of the shell is white, with a single muscle scar that is sometimes dark, but never purple or black.

Can be confused with: It differs from Crassostrea virginica in never having a purple or black muscle scar, and from Ostrea lurida in its extremely large size and heavy shell. In addition, the inside of an O. lurida shell is iridescent green.

Distribution

provided by FAO species catalogs
Cosmopolitan. Recorded from Japan, Korea, Siberia, Australia, United States and Canada. Introduced in North America is found Southeast Alaska to Baja California. In Europe from the British Isles south to Portugal and in the Mediterranean.

Size

provided by FAO species catalogs
Maximum length is 30 cm (exceptional specimens can attain 40 cm), but normally the length is from 8-15 cm.

Brief Summary

provided by FAO species catalogs
Is an exotic species introduced into west coast estuaries americaines from Japan. Prefer firm bottoms, and usually attach to rocks, debris or other oyster shellsat depths of between 5 and 40 m.However, they can also be found on mud or mud-sand bottoms. Pacific oysters are protandrous hermaphrodites. They change sex, but their timing is erratic and seasonal. Spawning depens on a rise in water temperatures above eighteen degrees Celsius. When spawning does occur, it occurs primarily in July and August; eggs (50-100 millions in single spawning) and larvae are planktonic distributed throughout the water column in estuarine waters. Later stage larvae settle out of the water column and crawl on the bottom searching for suitable habitat before settling.

Juveniles and adults are sedentary and are found in lower intertidal areas of estuaries.

Benefits

provided by FAO species catalogs
The commercial fishery for this species has grown rapidly since its introduction from Japan to the west coast of the United States in 1903. The United States now consumes almost 60 percent of the world's total oyster production. The Pacific oyster is a dominant shellfish in a growing United States aquiculture industry along the Pacific Coast. The 60-70 percent of the Pacific oyster production is marketed in the Pacific Coast States.The total catch reported for this species to FAO for 1999 was 12 271 t. The countries with the largest catches were Korea, Republic of (11 609 t) and USA (539 t).

Habitat

provided by Invertebrates of the Salish Sea
Firm sediment or rocky beaches
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Dave Cowles
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Distribution

provided by Invertebrates of the Salish Sea
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.
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Habitat

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Depth Range: Intertidal to 6m
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Comprehensive Description

provided by Invertebrates of the Salish Sea
Oysters have two thick, irregular valves, but one of them is usually cemented to the substrate. The valves are usually higher than long, have no "wings" near the hinge, and have no regularly spaced radial ribs. Crassostrea gigas grows up to 25 cm high and has conspicuous frills on its valves. Gray-white shell; often new growth is purplish-black. Inside is smooth and white. The left valve is usually larger and cupped, while the upper valve is usually slightly smaller and flat.
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Rosario Beach Marine Laboratory
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Look Alikes

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How to Distinguish from Similar Species: This is the largest local oyster; and usually the most commonly encountered one. The other introduced oyster and the Olympic oyster do not have the conspicuous frills on the valves and grow to no larger than 15 cm high.
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Rosario Beach Marine Laboratory
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Dave Cowles
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Invertebrates of the Salish Sea

Comprehensive Description

provided by Invertebrates of the Salish Sea
Biology/Natural History: The shape of this oyster is quite variable. The species was introduced from Japan in the early 1900's 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. 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 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 and become toxic to eat.
license
cc-by-nc-sa
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Rosario Beach Marine Laboratory
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Dave Cowles
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Invertebrates of the Salish Sea