The Eastern oyster (Crassostrea virginica) has been associated with the Chesapeake Bay for hundreds of years. Also known as the American or Virginia oyster, the eastern oyster is a bivalve with two rough, whitish shells. It forms reefs in brackish and salty waters throughout the Bay. For more than a century, oysters have made up one of the region’s most valuable commercial fisheries, and the filter-feeder continues to clean our waters and offer food and habitat to other animals. But over-harvesting, disease and habitat loss have led to a severe drop in oyster populations. Scientists are working to manage harvests, establish sanctuaries, overcome the effects of disease and restore reefs with hatchery-raised seed in an effort to bring back the bivalve.
Oysters are natural filter feeders. This means they feed by pumping water through their gills, trapping particles of food as well as nutrients, suspended sediments and toxic contaminants. In doing so, oysters help keep the water clean and clear for bay grasses and other aquatic life. One oyster can filter more than 50 gallons of water in a single day.
As oysters grow, larvae settle on top of adults, forming layers of oysters that spread upward and outward. With their countless nooks and crannies, these aquatic reefs provide habitat to hundreds of critters, from small fish and invertebrates seeking shelter to larger fish looking for food. Oysters have a number of natural predators, from other filter feeders that feed on oyster larvae to shorebirds that feed on exposed adult oysters.
Since the late nineteenth century, the oyster industry—including the catch, sale, shucking, packing and shipping of oysters—has contributed millions of dollars to the region’s economy. At the turn of the twentieth century, the Bay’s oyster fishery was one of the most important in the United States. But over-harvesting removed huge volumes of oysters from the Bay and led to the demise of the Bay’s healthy reefs. Currently, jurisdictions manage oysters for multiple uses by designating areas for harvest, aquaculture and sanctuaries (no harvest).
The continuous decline has also been attributed to other factors including disease and habitat loss. Overcoming the effects of two common oyster diseases in the Bay, Dermo and MSX, has posed a challenge to oyster restoration. It is estimated that by age three, 80 percent or more of a single oyster year class in a high-disease area (like the Virginia portion of the Bay, for example) will die due to disease. Additionally, the watershed has experienced a change in land use over the past century, as urban, suburban and agricultural areas have replaced forested lands. This has increased the amount of nutrients and sediment entering our rivers and streams and contributed to the poor water quality that affects oysters and other aquatic life.