Charles G. Hardy, Jr., age 7, of High Point, North Carolina, for his question:
Why does an oyster change his sex?
The world of nature is full of surprises and if we poke around long enough, we find that almost anything is possible. More than a million species are designed to hand on life, yet no two methods are exactly alike. At present, researchers are still investigating and describing the various procedures. Perhaps they are too busy to wonder why this or that is so. In any case, nobody has come up with a good explanation of why an oyster changes his sex.
Some years ago, medical experts figured out how to change the sex of certain human beings. The operation is said to be very complicated, expensive and successful to some extent. When we hear these newsy events, some of us raise our eyebrows and wonder why. Meantime, certain oysters perform this switch with no trouble at all. It seems to be part of their normal reproductive cycle and they have no say in the matter. What's more, they cannot wonder why because they have no brains for serious contemplation of any sort.
Even brainy biologists are bewildered by this problem. It does not seem to be a necessary part of oyster reproduction, because many species do not change their sex. For example, among the common oysters of the Atlantic coast, the males remain males and the females remain females all their lives. Other oysters of European waters do reverse their sexes about every five years. So does the native oyster of our Pacific coast.
Nobody can say for sure why the change is made, but it does not interfere with the yearly production of infant oysters. As you can imagine, it is not easy to study sex changes in their natural habitat. As a rule, the changeable species share tidal pools with nonchangeable oysters. Both European and Japanese oysters have been established in our Pacific coastal waters.
In any case, the sex change is completed before the spawning season. When the water reaches a comfortable 66 degrees to 70 degrees, a certain number of last year's mammas and papas are ready to reverse roles. Oysters, of course, are firmly embedded on the sea floor and unable to move around for dating and mating. The males and females release their sex cells into the water where some of the pairs meet and fertilize each other. In most species, the young larvae spend a few hazardous weeks swimming around in the hungry sea. But the larvae of the Pacific oysters develop inside the female's shells and their infancy is less risky.
Oyster larvae look like miniature melon seeds, wearing toupees. They wave their hairy wigs to swim through the water, in search of food scraps. Most of them are devoured by fishes and other sea dwellers. In a day or so, they grow tiny, glassy shells, though their waving wigs continue to propel them around for about two weeks more. Then the few lucky survivors sink to the bottom and stay there for the rest of their lives.