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The Olympia oyster, Ostrea lurida, is the only oyster native to the West Coast of the United States. Around the turn of the 20th century, Olympia oysters were heavily harvested from Washington and Oregon for a booming San Francisco market. These small oysters were renowned for their distinctive, coppery flavor. A combination of unsustainable harvest, habitat degradation, pollution, and disease has caused the Olympia oyster population to plummet and remain very low.
Oysters are bivalves, a type of mollusk characterized by two opposing shells, or valves. They are related to clams, mussels, and other commonly known and often edible mollusks. They feed by filtering small particles from seawater. Many oysters, like other bivalves, release sperm and eggs separately in the water, where they meet and fertilize to form embryos outside the body of the mother. But Olympia oysters retain eggs within the mother’s shell. They “brood” their embryos for several weeks before releasing the young, now called larvae, into the water column. All oysters and most bivalves produce larvae, which are generally less than a millimeter in length. The larvae swim, eat, and develop in the water for several weeks to several months. They then search for a hard surface on which to settle and metamorphose into a juvenile oyster. Once settled, they are cemented to the substrate and remain there for the rest of their lives.
Oysters are important in regulating the health and diversity of the estuarine ecosystem. Because they feed by filtering phytoplankton and bacteria from seawater, a sizeable oyster population can reduce the amount of algae in the bay and help control water quality. The beds that form when oysters settle near each other help stabilize the muddy bottom of the estuary and may improve habitat conditions for eelgrass, an important estuarine plant. The hard, complex surfaces provided by groups of oysters provide a unique habitat in which other estuarine animals can hide, settle, or lay eggs. In this way, a substantial oyster population could increase species diversity. A number of restoration efforts are currently underway to restore Olympia oyster beds along the west coast of the US.