top of page

American Oyster


American oyster

The American oyster is an iconic species of the Chesapeake Bay and other coastal waters of eastern North America. Historically, this species was so common and made such large reefs that it was a documented navigation hazard in some areas. Unfortunately, a history of overexploitation, pollution, and physical damage has reduced the American oyster population size to as low as one percent of its original abundance in some areas.


American oysters, like all true oysters, live a sessile lifestyle. After a short mobile phase in the plankton, juveniles settle on dead oyster shells or some other hard surface and permanently cement themselves in place. From then on, they build strong, calcium carbonate shells. In this manner, they form very large reefs that provide habitat for several other species of invertebrates and fishes. American oysters are filter feeders that strain plankton and other organic matter from the water above the surface of their reefs. In areas with high oyster densities, they can keep the water nearly free of floating matter. Each American oyster filters approximately 50 gallons of water per day.


American oysters reproduce via broadcast spawning, where several females release their eggs and several males release their sperm into the water column at the same time. This behavior increases the likelihood that eggs will be fertilized and decreases the likelihood that the eggs will be eaten by predators near the reef’s surface. These oysters are extremely productive, and a single female may release as many as 150 million eggs throughout her lifetime. When they hatch, all American oysters are male. Most of them reproduce at least once as male, but as they mature, some individuals change to female. This sex change is a result of the difference in energy required to make sperm and eggs. Small individuals can m