Eastern oyster

Eastern oyster
Oyster bed in the Marshes of Glynn, Brunswick, Georgia, USA
Conservation status
Vulnerable  (NatureServe)[1]
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Mollusca
Class:	Bivalvia
Order:	Ostreida
Family:	Ostreidae
Genus:	Crassostrea
Species:	C. virginica
Binomial name
Crassostrea virginica (Gmelin, 1791)
Synonyms[2]
Crassostrea floridensis Sowerby Dioeciostrea americana Orton, 1928 Lopha gibsonsmithi Macsotay & Campos, 2001 Ostraea floridensis G.B. Sowerby II, 1871 Ostraea reniformis G.B. Sowerby II, 1871 Ostraea rostrata Chemnitz, 1785 Ostrea borealis Lamarck, 1819 Ostrea canadensis Lamarck, 1819 Ostrea procyon Holmes, 1858 Ostrea triangularis Holmes, 1856 Ostrea virginiana Röding, 1798 Ostrea virginica Gmelin, 1791

The eastern oyster (Crassostrea virginica)—also called the Atlantic oyster, American oyster, or East Coast oyster—is a

Like all oysters, C. virginica is a

Unlike most bivalves, whose shells are aragonite, adult eastern oysters have calcite shells. The larvae, however, retain the aragonite shell of their ancestors. The specific gravity of the two types of shell is similar, so neither would confer a weight advantage over the other for a freely swimming larva.^[16] The transition to the thicker calcite shell in the adult of this species is thought to be an adaptation for defense against predators because the oysters are immobilized in exposed locations.^[16]

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  Side
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  Outside
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  Inside
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  Cluster of oysters
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  Oysters growing on a post

Life cycle

The life cycle of C. virginica consists of spawn, floating fertilized egg,

C. virginica has been used to study oxidative DNA damage caused by environmental heat stress.^[23] These studies indicated that heat shock driven oxidative stress induces increased oxidative damage in DNA (e.g. measured as 8-OHdG formation) and cellular apoptosis (programmed cell death) in the gills of American oysters.^[23]

Regional histories

New York–New Jersey Harbor Estuary

Chesapeake Bay

Before industrial harvesting

Before Columbus and the rise of industrial oyster operations, oysters abounded in the bay. Oysters first arrived in the Chesapeake 5,000 years ago,^{[citation needed]} and shortly after, local Indians began eating them. Archaeologists found evidence the local Native Americans returned to the same place to collect oysters for 3,000 years. John Smith, on a voyage up the Chesapeake, stated oysters "lay as thick as stones."^[24] In fact, the word Chesapeake derives from an Algonquian word meaning 'Great Shellfish Bay'.^[25] Because of the abundance of oysters filtering the waters of the Chesapeake, the water was much clearer than it is now. Visibility would sometimes reach 20 feet. When the English began settling the area, they evidently had a localized impact of the oyster population. One archaeological site measured oyster sizes near Maryland's old capital St. Mary's city from 1640 to 1710. In 1640, when the city was still small, oysters measured 80 mm, and in the city's maximum population in 1690, they measured to 40 mm. When the capital moved to Annapolis, the population moved with it, and by 1710, the oysters were back up to 80 mm.^[26] However, the effect of overharvesting would remain local until after the Civil War, when a combination of new technologies led to the removal of nearly all the bay oysters.

Industrial oyster harvesting

During the industrial revolution, several new technologies were introduced to the Chesapeake Bay area which allowed for more intensive oyster harvesting. First was the invention of canning. This allowed oysters to be preserved much longer, and created demand for oysters across the world. Secondly, the invention of the dredge enabled oyster harvesters to reach untouched depths of the Chesapeake. And finally, the proliferation of steam-powered ships and railroads made transportation more reliable, enabling merchants to sell oysters far and wide. Estimates for the harvest in 1839 give a figure of 700,000 bushels. After the Civil War, dredges were legalized, and harvesting exploded to 5 million bushels that year. By 1875, 17 million bushels were taken from the bay. The harvesting would reach its peak in the 1880s, with 20 million bushels being harvested from the bay each year.^[26] Not only were they being taken for food, but also oyster reefs, where oysters had built hills of their dead shells over thousands of generations, were being dredged out. Surplus oyster shells had many uses then. They were ground into mortar, used as filler in roads, and as a source of lime in agricultural fertilizer. By the 1920s, harvests would be down to just 3–5 million bushels per year because of overharvesting.

Decline and disease

Overharvesting eventually depleted the remaining oyster population in the bay to just 1% of its historical level, where it stands today. Oyster harvests began to decline in the 1890s. They were being taken much faster than they could reproduce. Also, many of the shells and reefs were being taken and not being replaced. Oyster spat need a hard surface on which to attach, and these were vanishing because of the destruction of oyster reefs. By the 1920s, harvests were down to 3–5 million bushels per year,^[26] stabilized for a time by returning oyster shells back to the bay. But in the 1950s, the weakened oyster population had to deal with the diseases "dermo" and MSX. These decimated the remaining oyster population. The parasites which carried the disease are alien to eastern waters, and they were thought to have been brought to the Chesapeake by Asian oysters. Currently, oyster harvests average less than 200,000 bushels a year.

Commercial value

The eastern oyster used to be of great commercial value. Due to the steep decline in the number of oysters in various traditionally harvested areas, primarily because of overfishing and diseases,

Harvestable size of a C. virginica oyster is 75 mm (3.0 in), which can take from 12 to 36 months, depending on temperature, salinity of the water, and food supply.[18] Salinity is a very important climatological variable that affects spatfall. Oysters do best where salinities range from 10 to 30 ppt; the range of 15 to 18 ppt is considered optimal.^[18] Typically, when salinity levels are less than 6 ppt, larvae will not settle and metamorphose into spat.^[29] In 2010, 665 miles of coastline were affected by the Deepwater Horizon oil spill.^[30] To keep the oil at bay and to spare the oystermen, the authorities of Louisiana made an unprecedented decision to maximize the fresh water flow through the region's canals to three times usual levels.^[21] At the mouth of the canals, salinity fell to almost zero, which was probably why most of the oysters died.^[21] Sujata Gupta ventured into the marshlands and Gulf of Mexico with Brad Robin, a man from a line of generations of oystermen in southeastern Louisiana. Robin and his crew threw a net over the side to haul in a catch.^[21] There were dozens of palm-sized oysters, but 75% of them were "boxes" or empty shells.^[21] However, as they traveled further towards the Gulf of Mexico, where the water was less salinity-stressed by the flush, only 20% of the haul came back as boxes, a promising sign the oysters are trying to come back.^[21] Gupta reported, "Now since there are so many empty shells scattered on the sea floor, the larvae have more to latch onto, improving their odds".^[21] However, salinity levels are not the only concern. Eastern oysters are filter feeders, so they are greatly affected by their surroundings since they are sessile organisms. This means if the water around them was contaminated with oil and the dispersant used to get rid of the oil, then these chemicals were collected by the oysters as they filtered the water.^[31] This is cause for great concern that the oysters are being killed by the toxins in the dispersant, as well.^[31] An added dilemma is oysters are in their weakest state after spawning season, which may have caused some of them to close their shells, resulting in death by suffocation within just a few days due to warm temperatures in the Gulf if the shells remain closed.^[31] The toxins in the oil and dispersants can also kill the larvae.^[31] To highlight the recovery of the state's oyster industry, the shell of C. virginica cut into cabochons was made Louisiana's official state gem in 2011.^[32][33]

Diseases

"Dermo" (