The eastern oyster (Crassostrea virginica) — also called Atlantic oyster or Virginia oyster — is a species of true oyster native to the eastern seaboard and Gulf of Mexico coast of North America. It is also farmed in Puget Sound, Washington, where it is known as the Totten Inlet Virginica.^[1] Eastern oysters are and have been very popular commercially. Today, less than 1% of the original 17th century population (when the original colonists arrived) is thought to remain in the Chesapeake Bay and its tributaries,^[2] although population estimates from any era are uncertain. The eastern oyster is the state shellfish of Connecticut,^[3] and its shell is the state shell of Virginia and Mississippi.

Description

Like all oysters, Crassostrea virginica is a bivalve mollusk with a hard calcium-carbonaceous shell. Its shell provides protection from predation.

This particular type of oyster has an important environmental value. Like all oysters, Crassostrea virginica is a filter feeder. They suck in water and filter out the plankton and detritus to swallow, then spit the water back out, thus cleaning the water around them. One oyster can filter more than 50 gallons of water in 24 hours.^[4] The eastern oyster also provides a key structural element within its ecosystem, making it a foundation species in many environments. Similar to coral reefs, oyster beds provide key habitat for a variety of different species by creating hard substrate for attachment and habitation.^[5] It is estimated that oyster beds have fifty times the surface area of an equally sized flat bottom. The beds also attract a high concentration of larger predators looking for food.^[6]

The Eastern oyster, like all members of the family Ostreidae, can make small pearls to surround particles that enter the shell. These pearls, however, are insignificant in size and of no value; the pearl oyster, from which commercial pearls are harvested, is of a different family.

History of the Chesapeake Bay oyster

Before industrial harvesting

Before Columbus and the rise of industrial oyster operations, there was an abundance of oysters in the bay. Oysters first arrived in the Chesapeake 5,000 years ago, 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."^[7] In fact, the word Chesapeake derives from an Algonquian word meaning 'Great Shellfish Bay'.^[8] 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, there is evidence they 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 80mm, and in the city’s maximum population in 1690, they measured to 40mm. When the capital moved to Annapolis, the population moved with it, and by 1710, the oysters were back up to 80mm.^[9] However, the effect of local 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

The industrial revolution would introduce several new technologies to the Chesapeake Bay area, which allowed for more intensive oyster harvesting. First, there 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 oysters being harvested from the bay each year.^[9] 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. There were many uses for the surplus oyster shells then. They were ground into mortar, used as filler in roads, and used as a source of lime in agricultural fertilizer. By the 1920’s, harvests would be down to just 3-5 million bushels per year because of overharvesting.

Decline and disease

Overharvesting would eventually deplete the remaining oyster population in the bay to just 1% of its historical amount, 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 to 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,^[9] 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 an alien to Eastern waters, and it is speculated they were 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,^[10] the annual catch has declined significantly. In Maryland, the 2006-2007 catch was 165,059 bushels (~7600 m³) of oysters.^[11] Other regions of the East Coast of the United States have successful oyster farms, including most notably Cotuit and Wellfleet on Cape Cod, in Massachusetts.

Diseases

"Dermo" (Perkinsus marinus) is a marine disease of oysters, caused by a protozoan parasite. It is a prevalent pathogen of oysters, causing massive mortality in oyster populations, and poses a significant economic threat to the oyster industry.

"MSX" (Haplosporidium nelsoni), another protozoan, was first described along the mid-Atlantic coast in 1957.^[12] Mortalities can reach 90% to 95% of the oyster population within 2 to 3 years of being seeded.^[13] MSX slows the feeding rates of infected oysters, leading to a reduction in the amount of stored carbohydrates, which in turn inhibits normal gametogenesis during spawning, resulting in reduced fecundity.

See also

• Oyster

References

Citations

Other sources

• Who Killed Crassostrea virginica? The Fall and Rise of Chesapeake Bay Oysters (2011), Maryland Sea Grant College (60 min. film)

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