Pacific oyster (South Sound marine life)

Pacific oyster (Crassostrea gigas)

Looking like a white rock among the cobbles, this Pacific oyster is unusual in that it is not in a clump of other oysters on a muddy sand beach.

Originally from Japan, this large mollusk was imported in the early 1900s, first to Samish Bay near Bellingham, then to Willapa Bay and south Puget Sound. It is distinguished from the native Olympia oyster by its white color, large size and flutes or ruffles on the shell. The Pacific oyster reaches harvest size in two years, two to three times faster than the Olympia oyster. The Pacific oyster can grow to 10 inches, but the Olympia oyster grows to only 3.5 inches. Both are filter feeders straining plankton from the water. The Pacific oyster can pump up to 60 gallons of water a day.

Oysters depend on their thick shells to ward off an attack by a crab or gull. However, small individuals still are vulnerable, and crabs can be a problem. In addition, ghost shrimp can affect oyster beds because of their burrowing activity, which softens the sediment. Oyster growers use various management tools to reduce the effects of predators or competitors on oyster beds.

Because oysters grow best in the low intertidal and shallow subtidal areas, growers usually spread seed or harvest using specially designed barges at high tide. Some growers hang oysters from beach structures and must tend them at low tide.

Seed oysters are obtained today from both oyster hatcheries and natural reproduction. Because the Pacific oyster requires warm water to mature and spawn, it does not do so on a regular basis in Washington. As a result, seed oysters were imported from Japan for many years, except during World War II.

Commercial oyster production in Washington was estimated at $58 million in 2000. The culture of oysters and clams has been important in this state for a long time. For instance, the first state Legislature passed several major laws that dealt with sale and use of tidelands for aquaculture.

David W. Jamison is a marine biologist and Boston Harbor resident.