An Oyster's Life By some standards, an oyster leads a dream life--breakfast in bed never ends. Snug in a tidal or subtidal mudflat, it can feed at its leisure, filtering up to eight gallons of salt water per hour to collect food in the form of detritus, tiny phytoplankton and the even smaller nannoplankton. An intertidal oyster doesn't have to hunt for food, but simply waits for the tide to bring the next serving. Oysters tend to live in clusters--communes if you will. The sexual happenings in one of these clusters depends on the kind of oyster. Members of the genus Ostrea,such as the Olympia oyster, are hermaphroditic--that is, they have both male and female reproductive organs. They first mature into males (in about one year), and then change to females after spawning. Alternation of sexes apparently continues throughout life. Clusters of Crassostrea,the Pacific oyster, also develop first as males. After the first year, the population divides into males and females, usually with no further sex reversal occurring. However, an occasional hermaphrodite has been found. Crassostreaoysters shed sperm or eggs into the water, where fertilization, hatching, and larval development take place. In Washington, this process occurs mid-summer, when water temperatures reach about 70° F. However, with Ostreaoysters, the males release sperm into the water, but the eggs are fertilized within the branchial chamber (space between the gills) of the female. The brood continues to develop for about 10 days before being discharged into the water column. Once in the water, larvae become part of the plankton community and gradually undergo several changes. After three to four weeks, the larvae are ready to settle on and attach to Oyster spat on a piece of cultch, approximately two months after setting. suitable substrates. At this time, oystermen place various kinds of material into the water to "catch" the larvae, in essence providing the young oysters with a home. This process is called "cultching." The catching materials are referred to as "cultch" and the recently settled oysters are known as "spat." Old shells from previously harvested oysters are commonly used as cultch. Natural spawning and setting occur together periodically in Washington state waters. The best areas for collecting oyster spat are in Dabob and Quilcene bays, in Hood Canal, and in Willapa Bay. The yearly setting frequency, however, has always been unpredictable. In some years catches of oyster spat exceed 50 per shell, in others no spat is caught. Recently, oyster growers have used oyster "setting" tanks to overcome this uncertainty. These tanks of seawater are aerated, heated to favorable levels, and filled with bags of clean shell to catch the seed. Free-swimming larval oysters are purchased from a shellfish hatchery and added to the cultch-filled (or lined) tanks. After a few days, the oysterman will have seed for the next crop of oysters. Life is not so rosy for the newly settled oyster though. Crabs, starfish and other predators love to feed on the youngsters. Mussels, barnacles, slipper shells and sponges may compete with them for space and food. Ghost shrimp can burrow into oyster beds, stirring up the mud that can smother young seed and ruin the best oyster-growing conditions. Oysters can also accumulate pollutants from the environment as they filter food from the water, slowing their growth, impairing breeding or even causing death. The luckiest oysters find safe homes on firm mud-sand in coves or bays, protected from scouring currents. There they can grow fat and healthy--at least until they are harvested, shucked and used in your favorite oyster recipes. (Also see water quality.) Return to Oysters Are Cool