THE PEARL OYSTER
Anatomy of an Oyster
Oysters are highly sensitve and quite complex creatures. The oyster like every other animal, possesses a heart, stomach, and mouth. It breathes through its gills and is able to move using its 'foot.'
An oysters age can be determined by the grooves in its hinge, just as one tells a tree's age from the rings in its trunk. The most interesting aspect of the oyster is the mantle. It is a fold of epithelial material that envelopes the animal and the halves of the mantle are joined together at the hinge. The outer edge is split into two parts: one covers the edge and crust of the shell and the other covers the mother of pearl which it produces through its epithelial cells. All pearls whether natural or cultured depend on this part of the mantle, so it is vital to be able to tell them apart so as to understand the process of pearl secretion.
Location and predators
Oysters are located at contrasting depths from very shallow waters to the edge of a Continental Shelf in 80 metres of water. Oysters survive best on a gravel or sandy bottom and prefer an open aspect, although some can be found in reefs. Enemies include octopus' and stingrays, and cyclones are known to cause a great deal of mortality as well as unseasonal changes in weather to which they are very sensitive.
Th oyster has the ability to change sex from male to female.When an oyster starts to breed it sets off a chain reaction with neighbouriong oysters. Eggs and semen unite at the mercy of the currents and the fertilised eggs remain in a plankton state for 20 to 30 days. By the 45th day, the oyster reaches a diameter of 10mm.
Oyster Habitat and Food
The oyster requires a flowing current to bring organic detritus to them, on which they feed, and is filtered through their system. Any other fragments such as sand and coral which come their way as they feed on the currents, are naturally filtered away, and generally do not pose a problem. It was thought that an irritating piece of grit was the basis of natural pearls, however the irritant is now believed to be a tiny marine worm or boring creature. When an oyster finds a suitable place to live, an organ situated in the foot secretes a fibrous matrerial, the byssus, which holds it in place to its location. The oysters attach themselves to suitable anchor points at depths of 15 to 20 metres and it is apparent that the light plays a major factor while deciding where to stay.