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Aquarium of the Pacific - Online Learning Center - Species Print Sheet

Conservation Status:  Invasive Species

Climate Change:  Vulnerable

Aquatic SpeciesPacific Oyster

Crassostrea gigas Mollusks, marine

Hand holding a large oyster | Brandi Kenney/Aquarium of the Pacific
Hand holding a large oyster - popup
Brandi Kenney/Aquarium of the Pacific

Species In-Depth | Print full entry

At the Aquarium

An exhibit featuring Olympia and Pacific oysters is located in the Pacific Visions Culmination Gallery. The Pacific oysters in the exhibit were provided courtesy of Carlsbad Aquafarm.

Geographic Distribution

This species is originally from Japan but has been introduced worldwide. They are now found along the West Coast of the United States, from Prince William Sound, Alaska, to Newport Bay, California.

Habitat

Pacific oysters are found cemented to rocks, other oysters, firm sediment, or other hard surfaces in sheltered intertidal waters up to 20 feet (6 m) deep in water temperatures of 46 to 72 degrees F (8 to 22 degrees C).

Physical Characteristics

This species is a large, sedentary bivalve mollusk, with the left valve typically attached to the substrate. It is usually larger and cupped, while the right (upper) valve is slightly smaller and flatter with folds or spine-like outgrowths that are often extremely sharp and rough. Pacific oysters generally have an elongate shell shape, without wings near the hinges as with most bivalves. The shell shape is extremely variable depending on substrate. The shell’s outer color is gray-white or off-white, with new growth often purplish-black and smooth. The shell is white on the inside, with a dark purple adductor muscle scar. The oyster’s flesh is off-white to beige in color with a dark edge.

Size

This species’ typical size is 3 to 15 inches (8-40 cm).

Diet

Pacific oysters are filter feeders that feed on phytoplankton, bacteria, protozoa, diatoms, and invertebrate animal larvae.

Reproduction

C. gigas changes sex during its lifetime, usually first spawning as a male then as a female the next year. Spawning usually takes place in the summer, as it is temperature dependent. Over 50 percent of the oyster’s body mass is devoted to reproductive capacity during spawning season. Females may produce 30 to 40 million eggs each spawning, releasing them at a regular interval rate of five to ten times per minute, which turns the water a milky color. Males release their sperm with the water normally expelled as they filter for food. Fertilization takes place in the water column.

Pacific oyster larvae are planktonic, spending several weeks moving through the water column using a larval foot in search of a suitable settlement location. Time spent in this stage is dependent on salinity, food supply, and water temperature. Over time they metamorphose and settle as small spat, attaching to a substrate and maturing into an adult oyster.

Behavior

Pacific oysters are sedentary, typically attaching to a substrate on their left valve.

Adaptation

Oysters are slower to adapt to changing conditions such as ocean acidification, ocean warming, and habitat destruction. They are able to tolerate short-term temperature increases and lower salinity. Most farmed oysters are raised under controlled conditions.

Longevity

This species may live twenty years or more.

Conservation

Although this species has been introduced worldwide, it is considered an invasive species as it outcompetes native species for space and food. Oysters are threatened by ocean acidification, habitat destruction, and pollution. Ocean acidification inhibits an oyster’s ability to form a shell. Oceans become more acidic as they absorb more carbon as a result of increased carbon emissions.