Pacific oyster

The genus Magallana is named for the Portuguese explorer Ferdinand Magellan 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. ==Description==

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: File:Crassostrea gigas 02.jpg|Right valve File:Crassostrea gigas 03.jpg|Left valve == Ecology ==

Habitat 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. ==Biology==

Sexuality 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. Life cycle The larvae of the Pacific oyster are planktotrophic, and are about 70 μm at the prodissoconch 1 stage. The expression of genes such as arginine kinase and cavortin is particularly important in regulating the metabolic response of this species to stress events including the reduction of seawater pH, as observed under ocean acidification. ==Aquaculture==

Historical background M. gigas was originally described by the Swedish naturalist Carl Peter Thunberg in 1795. It is now the most widely farmed and commercially important oyster in the world, as it is very easy to grow, environmentally tolerant, and easily spread from one area to another. Production statistics Global production has increased from about 150 thousand tonnes in 1950 to 1.2 million tonnes in 1990. By 2003, global production had increased to 4.38 million tonnes. This presents major issues for virus management of open-water shellfish farms, as shellfish like the Pacific oyster have been found to contain norovirus strains which can be harmful to humans. Diseases Various diseases are known to affect Pacific oyster: Predators Numerous predators are known to damage Pacific oyster stocks. Several crab species (Metacarcinus magister, Cancer productus, Metacarcinus gracilis), oyster drills, and starfish species (Pisater ochraceus, Pisater brevispinus, Evasterias troschelii, and Pycnopodia helianthoides) can cause severe impacts to oyster culture. In the preparations for the Tokyo 2020/2021 Summer Olympics, equipment for the canoeing and rowing was found to be contaminated with of M. gigas, necessitating US$1,280,000/£930,000 in removal expenditures. Ocean acidification Ocean acidification due to increasing atmospheric carbon dioxide impacts shellfish such as oysters. The increasing acidity of the ocean reduces oyster reproduction, lowers the survival rate of juvenile oysters, and causes delayed sexual maturation. Overall, these effects combine to lower recruitment to oyster populations, reduce the maximum sustainable yield that can be harvested, and reduce the profitability of oyster farms. It is unknown if acidification alters the flavor of shellfish or other qualities that make them desirable for human consumption. Productivity Productivity of the Pacific oyster can be described as the amount of meat produced in relation to the amount of seed planted on cultch. Aquaculture farmers at the time noticed the Pacific oyster outcompeted the endemic species, the Sydney rock oyster (Saccostrea glomerata), which naturally occurs in intertidal areas in the North Island. Early experiments in rock oyster cultivation procedures attached spat to cement-covered sticks and laid them down in racks. In 2006, the 23 Pacific oyster farms throughout New Zealand covered a total of 750 hectares of marine space and produced 2,800 tonnes of product per year. New Zealand's main export markets are Japan, Korea, the US, the EU and Australia. However, research has demonstrated that changes in global ocean temperature and the advent of ocean acidification may alter the growth, reproduction, and development of this species with variable responses ==See also==