All About Oysters
It’s easy to find an oyster shell on the beach. Some are worn smooth by wave action, but most have a fluted surface that gives them a decorative look. Turn one over, and the inside is smooth and white, with a smudge of purplish-brown.
The tasty meat of the oyster is highly prized. BC’s oyster industry harvests an average of 5500 tonnes a year, most of which are grown along the sheltered waters of eastern Vancouver Island. Oysters thrive here, and one would assume they have been around forever, but this is not the case.
The Pacific oyster (Crassostrea gigas), the species used for almost all oyster cultivation in the Pacific Northwest, actually hails from distant Japan. The story of the Pacific oyster begins in 1902, when Pacific oysters were first imported to Puget Sound. Oysters were introduced to BC in 1914. By the early 1930’s, over four million seed oysters had been brought into BC, most of which were planted in Ladysmith Harbour. In years following, the success of the Pacific oyster grew, and seed was planted in Boundary Bay, Pender Harbour, Baynes Sound, Cortes Island and many other areas.
Several other species from Japan have now become residents of the Pacific Northwest, having hitched a ride with the Pacific oyster. Some of these have become nuisance species that prey upon oysters, such as the oyster drill, a snail that bores through the oyster’s shell and sucks out its meat. Others, such as the Japanese littleneck clam, have become an important part of the shellfish industry. All in all, six species of shellfish, seven snails, four polychaete worms, and at least one species of seaweed have been introduced with the Pacific oyster, forever altering original ecosystems.
The Pacific oyster is a large oyster that can grow up to 45 cm long. The size, shape and surface texture of the shell is irregular. It tends to grow longer and smoother when grown on muddy surfaces, and broader and more fluted on firm surfaces. If left undisturbed, a Pacific oyster can live for 20 years or more.
Prior to the introduction of the Pacific oyster, the native or Olympic oyster was an important food source for first nations peoples, and was quite abundant. The Olympic oyster (Ostrea lurida) is much smaller than the Pacific oyster, and is roughly circular in shape, growing to less than 60 mm in diameter. Olympic oysters grow attached to rocks and other shells in mud or gravel flats near estuaries. The outside of the shell is grayish, and the inside is a smooth, iridescent olive-green. The Olympic oyster ranges from southern Alaska to southern Baja, California.
The Olympic oyster is now considered a species of special concern, due to declining populations. Some threats to the Olympic oyster include sedimentation from dredging and filling, pollution, temperature fluctuations, predation by introduced oyster drill snails, and being crowded out by the much more prevalent Pacific oyster. Oyster aficionados claim that the Olympic oyster has the best flavour of any oyster of the Pacific Northwest, and these oysters are grown commercially on a small scale.
The Eastern oyster (Crassostrea virginica) was introduced to Boundary Bay, BC in 1903 from Atlantic Canada. Unlike the Pacific Oyster, the Eastern oyster never did too well in BC waters, and today only small populations remain.
Oysters are bivalve molluscs, a group that include mussels, clams and scallops. They are characterized by have two protective shells, or “valves” that are joined together by a hinge. Bivalves have a soft body that is enveloped by a flap of tissue called a mantle.
Like other bivalves, oysters are filter feeders and feed upon microorganisms such as diatoms, dinoflagellates and bacteria, as well as tiny bits of decaying plant and animal matter. Oysters can change gender from male to female and vice versa depending on conditions. Female oysters produce quantities of eggs, which are fertilized by the male’s waterborne sperm. After fertilization, newly hatched larvae swim freely for one to two weeks before attaching to a hard surface, often on other oyster shells. Chemical signals enable larvae to find oyster shells to settle on. The process of attaching to a hard surface is called “spatting”. Oysters take 22-30 weeks to reach sexual maturity, and harvested when they are around three years old.
Oysters have long been an important food source to peoples around the world, and are considered by some to be an aphrodisiac. In nature, oysters are an important food source for the ducks, crabs, sea stars and snails.
Caution should be taken when harvesting oysters. Oysters feed upon dinoflagellates, creatures responsible for toxic red tides that often close shellfish harvesting for periods during the spring and summer months. At least one-quarter of BC’s beaches are closed to shellfish harvesting due to pollution. Safe oysters are locally available from several retail outlets.
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