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Pacific oyster
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Pacific oyster
The Pacific oyster, or Japanese oyster (Magallana gigas) is an oyster native to the Pacific coast of Asia. It has become an introduced species in North America, Australia, Europe, and New Zealand.
The genus Magallana is named for the Portuguese explorer Ferdinand Magellan and its specific epithet gígās is from the Greek for "giant". It was placed in the genus Crassostrea until 2017; from the Latin crass meaning "thick", ostrea meaning "oyster". In 2017, the WoRMS, following the DNA-based opinion of Salvi et al., moved all pacific members of Crassostrea to Magallana.
Parts of the scientific community resist this change and continue to argue that Crassostrea gigas should be the proper name. They argue that Salvi's DNA sampling is incomplete, and that criteria other than the genetic sequence should have been considered.
The shell of M. gigas varies widely with the environment where it is attached. Its large, rounded, radial folds are often extremely rough and sharp. The two valves of the shell are slightly different in size and shape, the right valve being moderately concave. Shell colour is variable, usually pale white or off-white. Mature specimens can vary from 80 to 400 mm long.
Right and left valve of the same specimen:
M. gigas is an estuarine species, but can also be found in intertidal and subtidal zones. They prefer to attach to hard or rocky surfaces in shallow or sheltered waters up to 40 m deep, but have been known to attach to muddy or sandy areas when the preferred habitat is scarce. The Pacific oyster can also be found on the shells of other animals. Larvae often settle on the shell of adults, and great masses of oysters can grow together to form oyster reefs. The optimum salinity for Pacific oysters is between 20 and 35 parts per thousand (ppt), and they can tolerate salinities as high as 38 ppt; at this level, however, reproduction is unlikely to occur. The Pacific oyster is also a very temperature tolerant species, as it can withstand a range from −1.8 to 35 °C.
The Pacific oyster has separate sexes, but hermaphrodites sometimes do exist. Their sex can be determined by examining the gonads, and it can change from year to year, normally during the winter. In certain environmental conditions, one sex is favoured over the other. Protandry is favoured in areas of high food abundance and protogyny occurs in areas of low food abundance. In habitats with a high food supply, the sex ratio in the adult population tends to favour females, and areas with low food abundances tend to have a larger proportion of male adults.
Spawning in the Pacific oyster occurs at 20 °C. This species is very fecund, with females releasing about 50–200 million eggs in regular intervals (with a rate at 5–10 times a minute) in a single spawning. Once released from the gonads, the eggs move through the suprabranchial chambers (gills), are then pushed through the gill ostia into the mantle chamber, and finally are released in the water, forming a small cloud. In males, the sperm is released at the opposite end of the oyster, along with the normal exhalent stream of water. A rise in water temperature is thought to be the main cue in the initiation of spawning, as the onset of higher water temperatures in the summer results in earlier spawning in the Pacific oyster.
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Pacific oyster
The Pacific oyster, or Japanese oyster (Magallana gigas) is an oyster native to the Pacific coast of Asia. It has become an introduced species in North America, Australia, Europe, and New Zealand.
The genus Magallana is named for the Portuguese explorer Ferdinand Magellan and its specific epithet gígās is from the Greek for "giant". It was placed in the genus Crassostrea until 2017; from the Latin crass meaning "thick", ostrea meaning "oyster". In 2017, the WoRMS, following the DNA-based opinion of Salvi et al., moved all pacific members of Crassostrea to Magallana.
Parts of the scientific community resist this change and continue to argue that Crassostrea gigas should be the proper name. They argue that Salvi's DNA sampling is incomplete, and that criteria other than the genetic sequence should have been considered.
The shell of M. gigas varies widely with the environment where it is attached. Its large, rounded, radial folds are often extremely rough and sharp. The two valves of the shell are slightly different in size and shape, the right valve being moderately concave. Shell colour is variable, usually pale white or off-white. Mature specimens can vary from 80 to 400 mm long.
Right and left valve of the same specimen:
M. gigas is an estuarine species, but can also be found in intertidal and subtidal zones. They prefer to attach to hard or rocky surfaces in shallow or sheltered waters up to 40 m deep, but have been known to attach to muddy or sandy areas when the preferred habitat is scarce. The Pacific oyster can also be found on the shells of other animals. Larvae often settle on the shell of adults, and great masses of oysters can grow together to form oyster reefs. The optimum salinity for Pacific oysters is between 20 and 35 parts per thousand (ppt), and they can tolerate salinities as high as 38 ppt; at this level, however, reproduction is unlikely to occur. The Pacific oyster is also a very temperature tolerant species, as it can withstand a range from −1.8 to 35 °C.
The Pacific oyster has separate sexes, but hermaphrodites sometimes do exist. Their sex can be determined by examining the gonads, and it can change from year to year, normally during the winter. In certain environmental conditions, one sex is favoured over the other. Protandry is favoured in areas of high food abundance and protogyny occurs in areas of low food abundance. In habitats with a high food supply, the sex ratio in the adult population tends to favour females, and areas with low food abundances tend to have a larger proportion of male adults.
Spawning in the Pacific oyster occurs at 20 °C. This species is very fecund, with females releasing about 50–200 million eggs in regular intervals (with a rate at 5–10 times a minute) in a single spawning. Once released from the gonads, the eggs move through the suprabranchial chambers (gills), are then pushed through the gill ostia into the mantle chamber, and finally are released in the water, forming a small cloud. In males, the sperm is released at the opposite end of the oyster, along with the normal exhalent stream of water. A rise in water temperature is thought to be the main cue in the initiation of spawning, as the onset of higher water temperatures in the summer results in earlier spawning in the Pacific oyster.
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