However, they are rarely killed by either low or high temperatures. Intertidal oysters are frequently subjected to rapidly changing temperatures, including freezing air during the winter months. South of Cape Fear to northeastern Florida, most oysters grow intertidally, in the area exposed between high and low tides, although there are some isolated subtidal oysters growing in South Carolina. Most east coast oysters north of Cape Fear, North Carolina, are subtidal, growing on bottoms that are covered with water throughout the tidal cycle. This frequently produces overcrowding and results in thin, elongated oysters. In southern waters there is a nearly continuous setting of spat during warm weather. Oyster shells that are purposely placed or planted to attract oyster larvae are known as cultch.Īfter attachment occurs, these small oysters are called spat. However, other oyster shells appear to be the most-favored surface. Almost any hard, clean surface is acceptable for attachment. Unless removed by some external force, the oyster will never move again. If a suitable surface for attachment is found, the larva secretes a fluid that cements the left shell permanently to the object. If a place for attachment cannot be found, the larvae sink to the bottom and die. After three to four weeks these larvae settle on the bottom where they must locate a hard, clean surface for permanent attachment. Limited locomotion is produced by controlled movements of the cilia, however tides and currents produce the greater movement. Free-swimming larvae develop in approximately 24 hours. The sperm and eggs are released directly into the water column where fertilization and the early stages of development occur. In South Carolina most spawning occurs from April to October and is intensive during the summer months. Individual oysters are capable of alternating sexes, although the sexes are, at any given time, separate. Spawning begins in the spring when water temperature exceeds 70 degrees F. The filtering action of oysters can play an important role in removing not only suspended sediments from the water column, but can cleanse the water of various pollutants. This ability to separate food from silt apparently allows oysters to survive in waters of high turbidity which occurs in many estuaries. Large amounts of silt are rejected in this manner. Matter brought into the shell, but not passed through the mouth, is collected by mucus on the gills and then discharged. Food particles retained by the gills are conducted by ciliary action to the mouth and then to the stomach of the oyster. The quantity of water pumped by a large, healthy oyster may approach four gallons per hour. Food and other particulate matter, suspended in the water, are drawn into the oyster by the motion of small, fringe-like whips called cilia located on the gills. Opening and closing of the valves are controlled by an adductor muscle attached to each shell. The oyster feeds by filtering food particles from the surrounding water. Oysters are not only palatable, but also contain a number of vitamins, minerals, carbohydrates and proteins. It is readily available and can be served in a variety of appetizing ways. The oyster is one of the most popular local seafoods. Although other oysters are grown on the west coast, no other commercially important oyster species occurs on the east coast. The South Carolina oyster fishery is based entirely on the eastern oyster, Crassostrea virginica. Saltwater Fishing Conservation and Ethics.Recreational Harvesting of Oysters and Clams.
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