Crassostrea gigas

 The shell can grow up 18 cm long. An off-white to yellow or bluish grey in colour, the shell often has deep purple patches. The left valve is deeply cupped with 6 or 7 bold ribs making the shell margin rough. The right valve is flat or slightly convex and has ribs corresponding to channels of left valve.Similar to Crassostrea virginica although this species lacks the crenulate shell margin and bold ribs of Crassostrea gigas. Crassostrea gigas was introduced from Portugal to Essex in 1926 as a commercial crop and has since established itself in the wild. It occurs naturally in Japan and south-east Asia. Crassostrea gigas is also known as the Portuguese or Japanese oyster.

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.

Oysters have two thick, irregular valves, but one of them (the left) is usually cemented to the substrate (or to another oyster, as above). 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 (right) valve is usually slightly smaller and flat.

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.

Cannuel and Beninger (2006) demonstrated that the inner demibranchs of the gills develop earlier than the outer demibranchs. Plication of the gill is also attained relatively late in ontogeny. The gills of early juveniles of the species are thus structurally and functionally different from those of the adult.

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.

Depth range based on 2 specimens in 1 taxon.

Environmental ranges
  Depth range (m): 0.762 - 6.5

Graphical representation

Depth range (m): 0.762 - 6.5
 
Note: this information has not been validated. Check this *note*. Your feedback is most welcome.

 Found on the lower shore and shallow sublittoral to a depth of around 80 m.

Depth Range: Intertidal to 6m

Habitat: Firm sediment or rocky beaches

De Japanse oester Crassostrea gigas of ‘creuse’, door veel mensen aanzien als een lekkernij, werd in 1969 in België geïmporteerd als alternatief voor de falende kweek met de lokale platte oester. Men dacht oorspronkelijk dat deze soort zich hier niet zou kunnen voortplanten vanwege het koude klimaat. Maar dat was fout! De Japanse oester heeft het hier goed naar haar zin en vestigt zich op alle mogelijke harde ondergronden (dijken, strandhoofden, mosselbanken, …), waarbij ze in concurrentie treedt met mosselen en andere lokale schaaldieren voor beschikbare ruimte en voedsel.

The Pacific cupped oyster Crassostrea gigas, seen by many people as a delicacy, was imported to Belgium in 1969 as an alternative to the failing farming of the local common oyster. It was originally thought that the species would not be able to reproduce here because of the cold climate. However, this proved to be incorrect. The Pacific cupped oyster is comfortable in Belgian waters and is able to attach itself to all kinds of hard substrates (dikes, groins, mussel banks…), while competing with mussels and other local shellfish for available space and food.

Dimethyl Sulfide or DMS is present throughout the ocean(1). It’s an important odor component of many fish and shellfish, including clams, mussels, oysters, scallops, crabs and shrimp(2-9). Where does it come from? Usually from the marine plants they feed on.

Many species of plants and algae produce DMS, but not all species produce significant amounts of it. Nearly all of these are marine, and they tend to be in closely related groups with other DMS-producers, including Chlorophyte (green) seaweeds, the Dinophyceae in the dinoflagellates, and some members of the Chrysophyceae and the Bacillariophyceae (two classes of diatoms). Other large groups, like cyanobacteria and freshwater algae, tend not to produce DMS. (10,11)

Why do these groups produce DMS? In algae, most researchers believe a related chemical, DMSP, is used by the algae for osmoregulation- by ensuring the ion concentration inside their cells stays fairly close to the salinity in the seawater outside, they prevent osmotic shock. Otherwise, after a sudden exposure to fresh water (rain at the sea surface, for instance) cells could swell up and explode. In vascular plants, like marsh grasses and sugar cane, it’s not clear what DMS is used for. (12,13)

Freshly harvested shellfish can smell like DMS because DMSP has accumulated in their tissue from the algae in their diet. Some animals, including giant Tridacna clams and the intertidal flatworm Convoluta roscoffensis, harbor symbiotic algae in their tissues, which produce DMSP; this may not be important to their symbioses, but for Tridacna, the high DMS levels can be a problem for marketing the clams to human consumers. After death, DMSP begins to break down into DMS. A little DMS creates a pleasant flavor, but high concentrations offend the human palate.(2,14)

Not all grazers retain DMS in their tissues, though. At sea, DMS is released when zooplankton feed on algae. It’s been shown in the marine copepods Labidocera aestiva and Centropages hamatus feeding on the dinoflagellate Gymnodinium nelson that nearly all the DMS in the consumed algae is quickly released during feeding and digestion.(15) This has a disadvantage for the grazing zooplankton. Marine predators, like procellariiform seabirds, harbor seals, penguins, whale sharks, cod, and coral reef fishes like brown chromis, Creole wrasse and boga, can use the smell of DMS to locate zooplankton to feed on. (8,16,17)

It’s not easy to measure how much DMS is released from the Ocean into the air every year. Recent estimates suggest 13-37 Teragrams, or 1.3-3.7 billion kilograms. This accounts for about half the natural transport of Sulfur into the atmosphere, is the conveyor belt by which Sulfur cycles from the ocean back to land. In the atmosphere, DMS is oxidized into several compounds that serve as Cloud Condensation Nuclei (CCN). The presence of CCN in the air determines when and where clouds form, which affects not only the Water cycle, but the reflection of sunlight away from the Earth. This is why climate scientists believe DMS plays an important role in regulating the Earth’s climate. (12,18)