Description:
Crassostrea gigas is one of four species of oyster (Phylum Mollusca) found along the B.C. coastline. It was intentionally introduced to the Pacific Northwest in the early 1900s from Japan and Asia for shellfish farming. This bivalve is big, growing up to 30 cm in length, hence its Latin name (crass = thick, ostrea = oyster, gigas = big). In contrast, our only native oyster, Ostrea lurida, grows to a maximum length of 9 am.
The two shells (or valves) are elongated and somewhat oval. The outer surface of the shell is rough and often frilled. Typically they are off-white, yellow or grayish colour, with purple or black indicating new growth. A hinge or ligament joins the two shells, which close to protect the soft body of the oyster.
The two shells (or valves) are elongated and somewhat oval. The outer surface of the shell is rough and often frilled. Typically they are off-white, yellow or grayish colour, with purple or black indicating new growth. A hinge or ligament joins the two shells, which close to protect the soft body of the oyster.
Ecology:
In the Pacific Northwest, Crassostrea gigas inhabit coastal areas from Alaska to California. They can be found attached to hard surfaces, such as rocks, debris and other oyster shells from the mid intertidal zone to depths of 40m, where they outcompete other sessile bivalves (blue mussels and native oysters) and macroalgae for space.
C. gigas is a filter feeder that feeds on plankton and other organic matter floating in the water. To feed, they open the two shells and draw water over their gills. Plankton is trapped in mucus on the fills and transported to the mouth for digestion. An individual oyster can filter 30 L of water per hour. In contrast, an individual blue mussel (Mytilus spp.) can only filter 2-3 L of water per hour.
C. gigas are preyed upon by crabs, sea stars, predatory snails, birds and mammals. Their thick shell and sharp ridges help deter predators, as does their strong attachment to a hard substratum.
C. gigas is a filter feeder that feeds on plankton and other organic matter floating in the water. To feed, they open the two shells and draw water over their gills. Plankton is trapped in mucus on the fills and transported to the mouth for digestion. An individual oyster can filter 30 L of water per hour. In contrast, an individual blue mussel (Mytilus spp.) can only filter 2-3 L of water per hour.
C. gigas are preyed upon by crabs, sea stars, predatory snails, birds and mammals. Their thick shell and sharp ridges help deter predators, as does their strong attachment to a hard substratum.
Life History:
Crassostrea gigas can live up to 30 years! The sexes are separate, although C. gigas can change sex from year to year, usually in the winter. Hermaphrodites also occur. C. gigas are broadcast spawners, meaning eggs and sperm are released into the water where fertilization takes place. In the Pacific Northwest, spawning usually occurs in July/August when water temperatures are warm. A single female can release 50 to 100 million eggs in a single spawning!! The fertilized eggs develop into larvae that float in the water column for 3-4 weeks before settling to the substratum, where the larvae will crawl in search of a suitable habitat to develop into juvenile oysters.
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