The eastern oyster — also called Atlantic oyster or Virginia oyster — is a species

Species

In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

 of true oyster native to the eastern seaboard and Gulf of Mexico

Gulf of Mexico

The Gulf of Mexico is a partially landlocked ocean basin largely surrounded by the North American continent and the island of Cuba. It is bounded on the northeast, north and northwest by the Gulf Coast of the United States, on the southwest and south by Mexico, and on the southeast by Cuba. In...

 coast of North America

North America

North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...

. It is also farmed

Aquaculture

Aquaculture, also known as aquafarming, is the farming of aquatic organisms such as fish, crustaceans, molluscs and aquatic plants. Aquaculture involves cultivating freshwater and saltwater populations under controlled conditions, and can be contrasted with commercial fishing, which is the...

 in Puget Sound

Puget Sound

Puget Sound is a sound in the U.S. state of Washington. It is a complex estuarine system of interconnected marine waterways and basins, with one major and one minor connection to the Strait of Juan de Fuca and the Pacific Ocean — Admiralty Inlet being the major connection and...

, Washington, where it is known as the Totten Inlet Virginica. 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

Chesapeake Bay

The Chesapeake Bay is the largest estuary in the United States. It lies off the Atlantic Ocean, surrounded by Maryland and Virginia. The Chesapeake Bay's drainage basin covers in the District of Columbia and parts of six states: New York, Pennsylvania, Delaware, Maryland, Virginia, and West...

 and its tributaries, although population estimates from any era are uncertain. The eastern oyster is the state shellfish of Connecticut

Connecticut

Connecticut is a state in the New England region of the northeastern United States. It is bordered by Rhode Island to the east, Massachusetts to the north, and the state of New York to the west and the south .Connecticut is named for the Connecticut River, the major U.S. river that approximately...

, and its shell is the state shell of Virginia

Virginia

The Commonwealth of Virginia , is a U.S. state on the Atlantic Coast of the Southern United States. Virginia is nicknamed the "Old Dominion" and sometimes the "Mother of Presidents" after the eight U.S. presidents born there...

 and Mississippi

Mississippi

Mississippi is a U.S. state located in the Southern United States. Jackson is the state capital and largest city. The name of the state derives from the Mississippi River, which flows along its western boundary, whose name comes from the Ojibwe word misi-ziibi...

.

Description

Like all oysters, Crassostrea virginica is a bivalve mollusk with a hard calcium

Calcium

Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...

-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

Filter feeder

Filter feeders are animals that feed by straining suspended matter and food particles from water, typically by passing the water over a specialized filtering structure. Some animals that use this method of feeding are clams, krill, sponges, baleen whales, and many fish and some sharks. Some birds,...

. They suck in water and filter out the plankton

Plankton

Plankton are any drifting organisms that inhabit the pelagic zone of oceans, seas, or bodies of fresh water. That is, plankton are defined by their ecological niche rather than phylogenetic or taxonomic classification...

 and detritus to swallow, then spit the water back out, thus cleaning the water around them. One oyster can filter up to 48 gallons of water in 24 hours.

The Eastern oyster, like all members of the family Ostreidae

Ostreidae

Ostreidae are the true oysters, and include most species that are commonly eaten under the name oyster. Pearl oysters are not true oysters and belong to the distinct order Pterioida....

, can make small pearl

Pearl

A pearl is a hard object produced within the soft tissue of a living shelled mollusk. Just like the shell of a mollusk, a pearl is made up of calcium carbonate in minute crystalline form, which has been deposited in concentric layers. The ideal pearl is perfectly round and smooth, but many other...

s to surround particles that enter the shell. These pearls, however, are insignificant in size and of no value; the pearl oyster

Pearl oyster

Pearl oysters are saltwater clams, marine bivalve molluscs of the genus Pinctada in the family Pteriidae. They have a strong inner shell layer composed of nacre, also known as "mother of pearl"....

, from which commercial pearls are harvested, is of a different family

Family (biology)

In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...

.

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." In fact, the word Chesapeake derives from an Algonquian

Algonquian languages

The Algonquian languages also Algonkian) are a subfamily of Native American languages which includes most of the languages in the Algic language family. The name of the Algonquian language family is distinguished from the orthographically similar Algonquin dialect of the Ojibwe language, which is a...

 word meaning 'Great Shellfish Bay'. 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. 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. 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, 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, the annual catch has declined significantly. In Maryland

Maryland

Maryland is a U.S. state located in the Mid Atlantic region of the United States, bordering Virginia, West Virginia, and the District of Columbia to its south and west; Pennsylvania to its north; and Delaware to its east...

, the 2006-2007 catch was 165,059 bushel

Bushel

A bushel is an imperial and U.S. customary unit of dry volume, equivalent in each of these systems to 4 pecks or 8 gallons. It is used for volumes of dry commodities , most often in agriculture...

s (~7600 m³) of oysters. Other regions of the East Coast of the United States have successful oyster farm

Oyster farming

Oyster farming is an aquaculture practice in which oysters are raised for human consumption. Oyster farming most likely developed in tandem with pearl farming, a similar practice in which oysters are farmed for the purpose of developing pearls...

s, including most notably Cotuit and Wellfleet on Cape Cod

Cape Cod

Cape Cod, often referred to locally as simply the Cape, is a cape in the easternmost portion of the state of Massachusetts, in the Northeastern United States...

, in Massachusetts

Massachusetts

The Commonwealth of Massachusetts is a state in the New England region of the northeastern United States of America. It is bordered by Rhode Island and Connecticut to the south, New York to the west, and Vermont and New Hampshire to the north; at its east lies the Atlantic Ocean. As of the 2010...

.

Diseases

"Dermo" (Perkinsus marinus

Perkinsus marinus

Perkinsus marinus is a prevalent pathogen of oysters, causing massive mortality in oyster populations. The disease it causes is known as "Dermo" ,and is characterized by proteolytic degradation of oyster tissues...

) is a marine disease of oysters, caused by a protozoa

Protozoa

Protozoa are a diverse group of single-cells eukaryotic organisms, many of which are motile. Throughout history, protozoa have been defined as single-cell protists with animal-like behavior, e.g., movement...

n parasite. It is a prevalent pathogen

Pathogen

A pathogen gignomai "I give birth to") or infectious agent — colloquially, a germ — is a microbe or microorganism such as a virus, bacterium, prion, or fungus that causes disease in its animal or plant host...

 of oysters, causing massive mortality in oyster populations, and poses a significant economic threat to the oyster industry.

"MSX" (Haplosporidium nelsoni

Haplosporidium nelsoni

Haplosporidium nelsoni is a pathogen of oysters, that originally caused oyster populations to experience high mortality rates in the 1950s, and still is quite prevalent today. The disease caused by H. nelsoni is also known as MSX...

), another protozoan, was first described along the mid-Atlantic coast in 1957. Mortalities can reach 90% to 95% of the oyster population within 2 to 3 years of being seeded. MSX slows the feeding rates of infected oysters, leading to a reduction in the amount of stored carbohydrates, which in turn inhibits normal gametogenesis

Gametogenesis

Gametogenesis is a biological process by which diploid or haploid precursor cells undergo cell division and differentiation to form mature haploid gametes. Depending on the biological life cycle of the organism, gametogenesis occurs by meiotic division of diploid gametocytes into various gametes,...

 during spawning, resulting in reduced fecundity

Fecundity

Fecundity, derived from the word fecund, generally refers to the ability to reproduce. In demography, fecundity is the potential reproductive capacity of an individual or population. In biology, the definition is more equivalent to fertility, or the actual reproductive rate of an organism or...

.

Other sources

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