National Geographic : 1927 Jan
LIFE ON A CORAL REEF is a pink one easily visible to the naked eye. It belongs to some gorgonian, as its odor testifies when it is crushed between the fingers, or as the very odor of the water in which the eggs are dipped up indicates. In a great outburst of reproductive ac tivity on the night before, very many, perhaps all the mature colonies of at least one of the common gorgonians, must have discharged these together. But for concentration of its spawning within narrow limits and for intensity of expression of the reproductive bent, surely nothing can surpass the various palolo worms, of which one is very com mon at Tortugas. Its annual breeding swarm is one of the outstanding events of the year in the life of the reef popula tion. WHEN NATURE DEMANDS ACTION The Tortugas palolo at maturity is a segmented worm about eight inches long. In appearance it shows marked resem blance to the clam worms of northern shores. It lives chiefly in burrows, origi nally made by other organisms, in the dead corals of the reef, and little is seen of it by one who does not take hammer and chisel and carefully chip it out. It is marvelously attuned to its surround ings. Each year, usually within three days of the last quarter of the July moon, it forgets its customary shyness. Then, before daylight, on the same day, prac tically all, male and female alike, protrude the hind end of the body from their hid ing places. These exposed ends, which contain all their developed egg and sperm cells and may measure more than half the length of the animal, they then proceed to cut off in a single piece by vigorous twisting which breaks the worms in two. The severed tails swim to the surface and may be found there at dawn in myriads. Scarcely a square foot over stretches of miles fails to show one or more of them. With the greenish female pieces the reddish males continue to writhe till sun rise, in the mazes of a witches' dance. Then at sunup, within a few minutes, all burst, spilling the germ cells in the water, which becomes at once turbid with them. Their office discharged, the shrunken remains of the fertile segments sink to the bottom and are lost. After a free swimming life of a few days, the larvae follow them to the depths to take up their buried life. The mutilated worms, in their burrows, grow their missing parts anew, and young and old alike remain in seclusion a twelve month more. THE FEASTING HOUR OF THE STRANGER This great natural time of reproduction lasts only a few hours at most, but the period of the swarm is for many of the fishes a combined field day, Sunday school picnic, and Fourth of July. Grunts, that eat worms freely at all times, are gorged with them. Groupers, that have tasted none for a year, are filled to reple tion, their trim lines marred by swollen maws. Snappers, that usually feed from the bottom and at daylight quit as promptly as a journeyman throws down his tools, are stirring actively long after their usual hour, with backs and fins breaking the surface in deep water. The tax levied upon the helpless worms is enormous. Twenty each was the esti mated spoil of fourteen snappers ex amined, and fishes of their size and sort occur on the reefs by scores of thousands. Thus the inroad upon the sum total can be imagined. BENEATII-THEI-SURFACE OBSERVATIONS The fertility of the sea is one thing, its mystery another by which I am always impressed. Here I think not of the vast reaches on which one may steam for a week and see not even a wisp of friendly smoke on the horizon; nor even of life in its deeps, from which our dredges bring up rare samples of the bizarre creatures that people them. What happens in ten feet of water is, perhaps, less well known than land events anywhere except in the crown of the tropical forest. Even if we knew the di urnal round of life at this slight depth which we do not-night life is so differ ent that an account of it would make a tale both novel and thrilling. Except audibly, even in the jungle, there is not greater change at dusk and dawn. Before I leave my work under water in the late afternoon I feel it im pending.