Eastern oyster facts for kids

Kids Encyclopedia Facts

Quick facts for kids Eastern oyster

Oyster bed on Cockspur Island, Georgia, USA
Scientific classification
Genus:	Crassostrea
Species:	virginica

The eastern oyster (Crassostrea virginica) is also known as the Atlantic oyster or American oyster. It's a type of true oyster that naturally lives along the eastern coasts of North and South America. You might hear it called by other names too, like the Wellfleet oyster or Blue Point oyster, depending on where it comes from.

These oysters live from Canada's New Brunswick all the way down to Brazil. People also farm them in many places, including the East Coast and Gulf states. They were even brought to the Hawaiian Islands a long time ago and are now common in Pearl Harbor.

The eastern oyster is very important for fishing and food. Sadly, its numbers have dropped a lot because its home has changed. For example, in the Chesapeake Bay, less than 1% of the oysters that were there when the first European settlers arrived are left today.

What is an Eastern Oyster?
Eastern Oyster Life Cycle
History of Chesapeake Bay Oysters
Commercial Value of Oysters
Effects of the BP Deepwater Horizon Oil Spill
Oyster Diseases
Recognition
Images for kids
See also

What is an Eastern Oyster?

Like all oysters, the eastern oyster is a bivalve mollusk. This means it's a soft-bodied animal with a hard shell made of calcium carbonate. This strong shell helps protect it from animals that want to eat it.

This oyster is super important for its environment. It's a filter feeder, which means it cleans the water! An oyster sucks in water, filters out tiny bits of food like plankton, and then spits the clean water back out. One oyster can clean over 50 gallons of water in just one day!

Eastern oysters also help create homes for other sea creatures. They are like "foundation species" because their oyster beds create hard places for many different animals to live and attach to. These beds can have 50 times more surface area than a flat seafloor of the same size. They also attract bigger animals looking for food.

Eastern oysters can make small pearls if something gets inside their shell. But these pearls are tiny and not worth money. The valuable pearls come from a different type of oyster called a pearl oyster.

Adult eastern oysters have shells made of a material called calcite. Baby oysters, called larvae, have shells made of aragonite, like their ancient ancestors. The calcite shell in adult oysters is thought to be a good defense against predators because oysters can't move once they settle down.

Eastern Oyster Life Cycle

The life of an eastern oyster goes through many stages. It starts with spawning, then becomes a floating egg, then different types of swimming larvae, and finally settles down to become a young oyster (called spat) and then an adult.

Oysters start spawning, or releasing their eggs and sperm, when the water gets warm. In northern areas, this happens between 60 and 68°F (15.5 and 20°C). In southern areas, it's when the water is warmer than 68°F (20°C). Spawning can happen all through the warm months.

Eastern oysters can become adults and reproduce when they are only four months old in warmer waters. Their reproductive cycle starts in late summer and fall when they store energy. This energy helps them create eggs and sperm in the winter and spring when there's less food.

From June to August, the eggs and sperm are released into the water, where they combine. Each female oyster can produce 75 to 150 million eggs! But only about one in a thousand eggs survives.

Fertilized eggs turn into tiny, free-swimming larvae in about six hours. These larvae have tiny hairs (cilia) that help them move and a small shell. After 12 to 24 hours, they grow into a veliger larvae, which has a hinged shell and a special "velum" for swimming and eating.

These larvae float in the water for about 2 to 3 weeks. Towards the end of this time, they develop an "eyespot" and a "foot." These larvae, called pediveliger larvae, then look for a hard surface to attach to. They prefer to attach to an adult oyster shell, but any hard surface will do.

Once a larva finds a spot, it glues its left shell to the surface. It then changes into an oyster spat. It loses its velum and foot, and its gills grow larger. During their first year, most young oysters are male. But after they reproduce once or twice, some males can change into females. Some females might even change back to males!

History of Chesapeake Bay Oysters

Oysters Before Industrial Harvesting

Before modern fishing methods, there were huge numbers of oysters in the Chesapeake Bay. Oysters first appeared in the Chesapeake about 5,000 years ago. Native Americans living there started eating them soon after. Archaeologists have found proof that Native Americans collected oysters from the same spots for 3,000 years.

When explorer John Smith sailed up the Chesapeake, he said oysters "lay as thick as stones." The name Chesapeake even comes from an Algonquian word meaning 'Great Shellfish Bay'. Because so many oysters were filtering the water, the Chesapeake Bay used to be much clearer. You could sometimes see 20 feet down!

When English settlers arrived, they started to affect the oyster population in local areas. For example, near Maryland's old capital, St. Mary's City, oysters were 80 mm long in 1640. But by 1690, when the city was at its biggest, oysters were only 40 mm long. When the capital moved, the oyster sizes went back up. However, serious overfishing didn't happen until after the Civil War.

Industrial Oyster Harvesting

During the Industrial Revolution, new tools and methods changed oyster harvesting. First, canning was invented. This meant oysters could be preserved for much longer, creating a demand for them all over the world. Second, the dredge was invented. This tool allowed oyster fishers to reach oysters in deeper waters that were untouched before. Finally, steam-powered ships and railroads made it easier to transport oysters far and wide.

In 1839, about 700,000 bushels of oysters were harvested. After the Civil War, when dredges became legal, harvesting exploded to 5 million bushels that year! By 1875, 17 million bushels were taken from the bay. Harvesting peaked in the 1880s, with 20 million bushels harvested each year.

Oysters weren't just taken for food. Oyster reefs, which are huge hills made of dead oyster shells built up over thousands of years, were also dredged out. These extra oyster shells were used for many things. They were ground into mortar for buildings, used as filler in roads, and as a source of lime for farm fertilizer. By the 1920s, harvests dropped to just 3–5 million bushels per year because too many oysters had been taken.

Decline and Disease

Overharvesting eventually caused the oyster population in the bay to shrink to just 1% of what it used to be. Oyster harvests started to decline in the 1890s because oysters were being taken much faster than they could reproduce. Also, many shells and reefs were removed and not replaced. Young oysters need a hard surface to attach to, and these surfaces were disappearing.

By the 1920s, harvests were down to 3–5 million bushels per year. For a while, returning oyster shells to the bay helped stabilize the population. But in the 1950s, the already weak oyster population faced new problems: diseases called "dermo" and MSX. These diseases killed off many of the remaining oysters. The parasites that cause these diseases are thought to have come to the Chesapeake from Asian oysters. Today, oyster harvests average less than 200,000 bushels a year.

Commercial Value of Oysters

The eastern oyster used to be very valuable for fishing and food. But because of the big drop in oyster numbers, mainly due to overfishing and diseases, the yearly catch has fallen a lot. For example, in Maryland, the catch in 2006–2007 was only about 165,059 bushels. However, some areas on the East Coast of the United States have successful oyster farms, like Cotuit and Wellfleet, Massachusetts, on Cape Cod.

Effects of the BP Deepwater Horizon Oil Spill

An eastern oyster needs to be about 75 mm long to be harvested. This can take 12 to 36 months, depending on water temperature, saltiness (salinity), and food supply. Salinity is very important for young oysters to settle. Oysters grow best when the water's saltiness is between 10 and 30 parts per thousand (ppt), with 15 to 18 ppt being ideal. If the salinity is less than 6 ppt, young oysters usually won't settle and grow.

In 2010, the Deepwater Horizon oil spill affected 665 miles of coastline. To protect the oysters and help the oystermen, authorities in Louisiana decided to release a lot of fresh water through the region's canals. This made the water at the mouth of the canals almost completely fresh, which likely killed most of the oysters there.

A reporter named Sujata Gupta visited the marshlands with an oysterman named Brad Robin. They pulled up nets of oysters, and 75% of them were "boxes," meaning empty shells. However, as they went further towards the Gulf of Mexico, where the water was less affected by the freshwater, only 20% of the oysters were empty. This was a hopeful sign that the oysters were trying to come back. Gupta reported that with so many empty shells on the seafloor, young oyster larvae had more places to attach, which improved their chances.

But salinity isn't the only concern. Eastern oysters are filter feeders, so they take in whatever is in the water. If the water was polluted with oil and the chemicals used to clean up the oil, then the oysters collected these toxins. This is a big worry, as these chemicals can kill the oysters. Also, oysters are weakest after spawning season. If they closed their shells due to the toxins, they could suffocate and die quickly in the warm Gulf waters. The toxins can also kill the oyster larvae.

To celebrate the recovery of the state's oyster industry, the shell of the eastern oyster, when cut and polished, was made Louisiana's official state gem in 2011.

Oyster Diseases

"Dermo" (Perkinsus marinus) is a disease that affects oysters. It's caused by a tiny protozoan parasite. This parasite is very common and causes many oysters to die, which is a big problem for the oyster fishing industry.

Multinucleated sphere X (MSX) (Haplosporidium nelsoni) is another protozoan parasite. It was first found along the mid-Atlantic coast in 1957. This disease can kill 90% to 95% of an oyster population within 2 to 3 years. MSX makes it harder for infected oysters to eat, which means they don't store enough energy. This stops them from making eggs and sperm properly, leading to fewer baby oysters.

Recognition

The eastern oyster is the official state shellfish of Connecticut. Its shell is the official state shell of Virginia and Mississippi. And its polished shell is the official state gem of Louisiana.