(A.K.A. American oyster)

The Eastern oyster is vital to the Chesapeake Bay ecosystem. Oysters consume algae by filtering water at a rate of up to 2 gallons per hour. In abundance, oysters help clarify the water, which allows Bay grasses to receive more sunlight. Plentiful grasses increase oxygen levels and reduce shoreline loss. Oyster reefs also provide excellent habitat for other aquatic life. Fish and crabs hide in the small crevices and holes created by the oysters and shells that make up the reef.

Oysters start life in the summer as tiny larvae which attach themselves to rocks, pebbles or shells. They prefer to connect to other oyster shells, and over many centuries, the buildup of generations of oysters creates large bars or reefs of shells and live oysters. Living oyster bars are made up of mostly dead shells with only a covering of live oysters on top.

Eastern Oysters have two shells which are generally grey in color. The shells are often much darker in spots due to algae and other encrusting organisms. The shells fit tightly together, forming a water tight seal when fully closed. As it grows the shell develops many bumps and ridges. Adult Eastern Oysters can grow to be about 8 inches long. Oysters found in the Chesapeake Bay are usually 4 to 5 inches long.

People all over the world love to eat oysters. The Chesapeake oyster industry, once the world’s largest, began to decline steadily throughout the late 19th and early 20th centuries. The recent rapid decline in the abundance of oysters has been attributed to the introduction of two foreign diseases, Dermo and MSX.

Environmental factors such as runoff also contribute to the loss of oyster habitat. Intensive efforts are underway to restore the oyster population. Information on current restoration efforts and studies is available at http://www.dnr.state.md.us/fisheries/oysters/

Illustration of Eastern Oyster is from
a 1902 Colorlitho by S.F. Denton

For more information:
Fish Facts: Eastern Oyster