At the Aquarium
An exhibit featuring Olympia and Pacific oysters is located in the Pacific Visions Culmination Gallery. The Olympia oysters in this exhibit are provided courtesy of California State University, Fullerton.
This species lives along the west coast of the United States, from Sitka, Alaska, to Baja California, Mexico.
Olympia oysters can be found attached to rocks or old oyster bed shells in estuaries, bays, and areas bordered by mudflats and in eel grass beds. They prefer water depths up to 233 feet (71 meters) and a water temperature range of 43 to 68 degrees F (6 to 20 degrees C).
This oyster is a bivalve mollusk with both valves roughly the same size. Genus Ostrea, known as flat oysters, have shells that aren’t deeply cupped. The upper (right) valve is fairly flat and fits into the concave lower (left) half. There are no wings near the hinge as with most bivalves and no regularly spaced radial ribs. Small chomata (folds on the inside of the shell) are present near the hinge ends. Their shell is thinner than that of most oysters and lacks periostracum, or organic coating, which is the outermost shell coating that prevents erosion of the underlying shell. The shell is whitish to purplish black or grayish-green and slightly pearly. The single adductor muscle scar is not much darker than the rest of the inside of the shell. Their flesh is white to light olive green. Adult oysters have either a reduced foot or none at all. They cement their left valve to a solid substrate with the valve conforming to the shape of the substrate.
Olympia oysters are typically 2.4 to 3.1 inches (6 to 8 cm) in length and 1.6 to 2.4 inches (4-6 cm) in width.
Olympia oysters filter the water for phytoplankton.
This oyster is a hermaphrodite. Spawning takes place between May and August, when the water reaches about 57.2 degrees F (14 degrees C). With the oyster’s first spawning cycle, it acts as a male. In following spawning cycles, it will switch between the sexes. Males release their sperm in the form of sperm balls from their mantle cavities. The balls dissolve into free-floating sperm in the water. Female’s eggs are fertilized in their mantle cavity, known as a brooding chamber, when the free-floating sperm are filtered into her gill slits. Fertilized eggs will then move into the branchial chamber (mantle cavity). The eggs will develop into veliger larvae. When the larvae, known as spat, leave the brooding chamber, they begin to develop a foot and eye spot. They will then migrate to find a hard surface, usually old oyster shells, where they will secrete a glue-like material from their byssus gland to attach themselves to the surface.
This sedentary oyster typically lies on its left valve, which is securely attached to the substrate.
This species is slower to adapt to changing conditions such as ocean acidification, ocean warming, and habit destruction. Most farmed oysters are now raised under controlled conditions.
Their maximum lifespan is unknown, but it is thought to exceed ten years.
This species has declined over the last 150 years due to overharvest, pollution, and habitat loss due to coastal development. Its disappearance from the San Francisco Bay area began with the California Gold Rush. They were overharvested and experience severe silting due to hydraulic gold mining in the Sierra Nevada Mountains.
Oysters are threatened by ocean acidification resulting from climate change. Increased carbon emissions result in more carbon being absorbed by the ocean, making it more acidic. More acidic ocean water inhibits young oysters’ ability to form shells. Restoration efforts are now taking place in Puget Sound, Washington; Netarts Bay, Oregon; and San Francisco Bay, California. With efforts by conservancy groups and new laws, the wild species is becoming more stable.