The Eastern oyster is treasured as food by humans and other species. They are habitat for fish, crabs, and other critters—and because as filter feeders, they help filter the water. Centuries ago, they were plentiful. In some places, reefs were so big that ships had to navigate around them. Since then, in many areas, the populations have dwindled to just a few percent of what they once were. This is due to disease, overharvesting, habitat loss, and poor water quality. 

Appearance

• Reaches 8 inches at maturity.
• The shell has smooth edges and is oval in shape. The inside of the shell is white to off-white to brownish in color.
• The shell has a “cupped” shape to it, giving rise to its alternate name “American cupped oyster.”

Biology

• Are of the shellfish family. Like mussels, clams and scallops they are bivalve mollusks, and have a hinged shell.
• Adults are sessile—they stay in one place—and inhabit both intertidal and subtidal areas.
• Have fast growth rates and high reproduction rates.
• First mature as males, then later develop female reproductive capabilities.
• Each female can produce over 100 million eggs during a spawning event.

Where They Live

Range

• Eastern oysters are found along eastern North America from the Gulf of St. Lawrence to the Gulf of Mexico. They are found in the middle and lower Chesapeake Bay and its rivers. They are the only species of oyster native to this region.

Habitat

• Eastern oysters live in brackish and salty waters from 8 to 35 feet deep. In some warmer areas, they are able to live in the intertidal zone. They attach to firm bottom areas, and to each other, to grow into reefs. These reefs provide habitat for fish, crabs, invertebrates, macrofauna, and birds.

Are Eastern Oysters Sustainable?

U.S. farmed Eastern oysters are a smart seafood choice because they are sustainably grown and harvested under U.S. state and federal regulations.

Availability

Available year-round.

Source

Estuaries, mainly the East Coast or Gulf of Mexico.

Taste

Ranges from sweet to briny.

Health Benefits

Oysters are low in saturated fat and excellent sources of omega-3 fatty acids and iron.

Nutrition Facts

Servings: 1; Serving Weight: n/a; Calories: 81; Protein: 9.45 g; Total Fat: 2.3 g; Total Saturated Fatty Acids: 0.5 g; Carbohydrate: 0 g; Total Sugars: 0 g; Total Dietary Fiber: 0 g; Cholesterol: 50 mg; Sodium: 106 mg

Understanding the Risks

Each year millions of Americans enjoy eating raw oysters. However, some people with certain medical conditions are at high risk for becoming seriously ill and dying from eating raw oysters. The U.S. Food and Drug Administration (FDA) is advising these high-risk individuals not to eat raw oysters, and to only eat oysters that have been thoroughly cooked.

The Cause: Vibrio vulnificus

Vibrio vulnificus (V. vulnificus) is a bacterium that occurs naturally in warm coastal areas, such as the Gulf of Mexico. Vibrio vulnificus is found in higher concentrations in the summer months as water becomes warmer.

Oysters feed by filtering water-surrounding areas where vibrios may thrive and as a result concentrate V. vulnificus in their tissues. When a person eats these shellfish raw or undercooked, the bacteria enter the digestive tract and multiply rapidly. In addition to ingestion, high-risk individuals can become infected when cuts, burns or sores come in contact with seawater containing V. vulnificus.

The Risk Factors

While not potentially life-threatening to most healthy people, symptoms of V. vulnificus infection may occur within 24 to 48 hours of ingestion and may include sudden chills, fever, nausea, vomiting, diarrhea, shock and skin lesions. In people with certain medical conditions such as cancer, diabetes or liver disease death can occur within two days. Anyone showing signs of any these symptoms after eating raw oysters should seek medical attention immediately.

Certain health conditions put people at high risk for serious illness or death from V. vulnificus infections. Some of these health conditions may be present without any symptoms so people may not know they are at risk. Individuals should check with their doctors if they are unsure of their risk. Vibrio vulnificus infections in high-risk individuals have a 50 percent fatality rate.

These conditions include:

• Liver disease (from hepatitis, cirrhosis, alcoholism, or cancer)
• Iron overload disease (hemochromatosis)
• Diabetes
• Cancer (including lymphomas, leukemia, Hodgkin's disease)
• Stomach disorders
• Or any illness or medical treatment that weakens the body's immune system, including HIV infection

Drinking Alcoholic Beverages Regularly and Liver Disease

People who drink alcoholic beverages (including beer and wine) regularly may be at risk for liver disease, and, as a result, at risk for serious illness or death from consuming raw oysters. Even drinking two to three drinks daily can contribute to the development of liver disease, which may occur without symptoms. Alcoholism and infections from Hepatitis can injure the liver and impair its function years before an individual begins to experience symptoms. Liver disease puts people at risk for V. vulnificus infection from raw oysters. The risk of death is almost 200 times greater in those with liver disease than those without liver disease.

Reducing Risk

Vibrio vulnificus bacteria are not a result of pollution, so although oysters should always be obtained from reputable sources, eating oysters from "clean" waters or in reputable restaurants with high turnover does not provide protection. Eating raw oysters with hot sauce or while drinking alcohol does not kill the bacteria, either. Only heat can destroy the bacteria.

Since thoroughly cooking oysters will destroy the bacteria, oysters can continue to be enjoyed in many cooked preparations by following this advice.