Part 13

The Ocean’s Sound Barrier

A densely woven carpet of life covers the floor of the world of light under the sea—just below the level reached by the most penetrating rays of the sun. It is a carpet of many colors and of flashing lights, the strands of its texture rapidly moving, predaceous, warring organisms. They probably are a mixture of lantern-carrying fish, ten-tentacled squid with malevolent red eyes, and small, luminous, shrimp-like creatures known as euphasids. Their nature can only be deduced by the echoes of sound from their bodies.

This carpet, about 300 feet thick, is the sea’s “false bottom.” It was discovered by Navy ships making depth soundings during the war. Such soundings depend on the time taken for echoes to be reflected to the surface from the ocean floor. Recorded on a ship’s instruments, they represent an extremely precise procedure perfected to the point where a continuous record of depth can be obtained with an accuracy of a few inches.

But, using certain wavelengths of sound, echoes were received from depths between 1,000 and 1,500 feet, whereas the sea itself was known to be two or three miles deep at these places. The only plausible explanation was that there were vast multitudes of floating or swimming objects of some sort, constituting almost a solid surface, at the depths from which the echoes came. The mystery was increased by the fact that the false bottom existed only during daylight. The carpet was laid shortly after sunrise and rolled up at twilight. The indication was that the echo-producing objects rose to the surface at the beginning of darkness—a clue which has given rise to much speculation and argument.

The carpet is under all the oceans, even the nethermost Antarctic. In some areas it seems practically continuous over thousands of square miles. In others it is broken up into smaller areas, like scatter rugs on a floor.

The false bottom is almost as much a mystery today as when it first puzzled the Navy’s navigators. All are agreed that it must be composed of vast hordes of animals. They are not directly observable by any known technique. Some indication of their size and abundance, however, can be deduced from the wave lengths of sound which they echo. There must be, it has been calculated, from ten to twenty of these organisms in each cubic meter of water. They echo only long sound waves. High frequency sound passes through them like light through glass and is bounced back from the true sea bottom. They have been a mild nuisance, but never a peril, to modern navigators.

Whatever the organisms may be, they evidently cannot endure any light. At dawn they sink immediately from within about 100 feet of the surface through the zone of moonlight-pale, green illumination which represents sunshine’s deepest penetration of sea water.

Chief proponents of the theory that a preponderance of them are squid are oceanographers of the Navy’s Hydrographic Office. It is well established that the deep sea abounds in these fantastic mollusks. They rarely are seen at the surface. They move through the water very rapidly by a kind of jet propulsion, gulping water in the mouth and shooting it out explosively from the rear. They are little affected by changes in hydrostatic pressure, as are fish with air bladders. When the false bottom rises at sunset it comes to the surface at a rate of forty to fifty feet a minute. No swimming fish, it is maintained, could rise so rapidly through the decreasing pressure. It would get the “bends”, like a human diver brought to the surface in too great a hurry.

These squid range in length from three or four inches to more than a foot. They are of about the right size to return some of the echoes which have been observed. The faintly luminous euphasid shrimps also are known to be very abundant in the depths. Presumably they provide most of the squids' food.

The principal investigations have been carried out by the Navy’s Electronics Laboratory and the Scripps Institute of Oceanography of San Diego. An outstanding difficulty hitherto has been that the echoes have been known only from the false bottom as a whole. They have covered a wide spectrum of sound wavelengths. A recently developed technique is to lower a hydrophone connected with a sound-producing mechanism into the depths in order to record echoes from individual objects at distances of a few feet. Indications to date are that some of them are from a foot to eighteen inches long—too large to be squid and far too large to be shrimp. They can only, it is deduced, be deep water fish. If a great number of fairly large fish are indicated, this false bottom might turn out to be the richest pasture in the ocean for the production of food for man.

Navy divers have swum through the false bottom at night when it was within less than 200 feet of the surface. They have observed enormous numbers of euphasids and other small organisms—but very few fish. This, however, is only suggestive. There is no good reason to believe the carpet has the same texture at night as by day. It is quite likely that the organisms disperse widely over the surface waters.

Snakes That Act and Look Like Worms

There are snakes that look like snarls of six-inch-long pieces of wrapping twine. These worm snakes are the world’s closest imitators of worms. Among the most secretive of living things, they rarely come in contact with man. When they are seen they usually are mistaken for worms. Only zoologists can put them in their true families. These living strings live exclusively under the earth, sometimes in tangled snarls of scores of individuals.

They are the smallest of snakes. Their closest relatives, however, are the gigantic boas and pythons. Judging from their wide distribution—on such isolated spots, for example, as Christmas Island in the Indian Ocean—they are quite ancient reptiles whose wanderings started about fifty million years ago.

They are found most often in termite nests, where they eat the eggs and possibly the larvae. Small earthworms and other soil creatures add to their diet. The worm snakes are almost toothless. Eyes are buried under skin, are only faint spots, and probably only can discriminate light from darkness. The tail looks somewhat like the head—a likeness presumably developed as a camouflage. They retain a snake’s scales, but these are highly polished so they can be of no help in crawling.

These Typhlopidae and Glauconidae, as the two major groups are known, are extremely active. When they are exhumed they start at once to burrow back and have been found as much as two feet underground. Occasionally they may be found in mole holes or in rotten wood where they feed on insect larvae and also, it is likely, get some warmth from the decay process. The snout is used in burrowing. They are hard to hold in the hand, owing to the high polish of the scales. There are approximately 100 species scattered over the world, two coming as far north as the Texas border. They have teeth in only one jaw—the upper jaw for Typhlopidae, the lower for Glauconidae.

A Porcupine of the Sea

Among the weirdest creatures of the deep is also one of the latest to become known to science—the sea urchin (closely related to star fish) astropyga magnifica. It is the largest sea urchin yet found in the Atlantic. It has approximately 200 bright blue eyes arranged in double rows. The body is covered with several hundred sharp, barbed black spines nearly a foot long.

That so conspicuous an animal, living in such a densely populated region—one of the most intensively studied in the world by biologists—should have remained undiscovered so long probably is due to two reasons. First, if its habits are at all comparable to those of its nearest relatives, it is strictly nocturnal and comes out to forage on the coral sands of the shallow sea bottom only after light has ceased to penetrate the water. During the day the creatures remain secluded, often congregated in great numbers, in holes and caves of the sea floor and under the coral.

Second, it is quite similar in appearance to another smaller member of the sea urchin race with spines as much as 18 inches long which is greatly dreaded and is even reputed to have caused the death of children who have fallen on it. Anybody coming upon a daytime bed-chamber of these fantastic creatures would be likely to leave them strictly alone.

This particular sea urchin is especially interesting in the development of its eyes. These appear to be true sight organs. If a hand is placed in the water near one of the animals the long barbs immediately are pointed in the direction of the intrusion, and as the hand moves the barbs move. Such a creature is practically impregnable. It never, however, takes the offensive. It cannot “throw” its barbs, but they enter the flesh easily and cause painful local irritation. Some species inject a virulent poison which may even kill a human being. There is no evidence that this species is toxic.

Astropyga magnifica, which has more the appearance of a porcupine than of any other land animal, is a scavenger of the sea bottom. It gathers and devours the accumulated debris that falls through the water. It never kills its own food, so far as is known. It has five sharp teeth in its mouth, located on its under surface, with which it can chew away the flesh of dead animals.

This sea porcupine has a peculiar system of locomotion in common with most of its relatives. It has literally thousands of sucker-like feet, which are hollow and attached to tubes within its shell. It moves by forcing water through the tubes and into the particular “feet” which it wishes to use. When these are out of use they are contracted by withdrawing the water. Being a radially symmetrical animal, the creature can move with equal ease in any direction. It has no head—that is, the development of its nervous system and the direction of its locomotion are not fixed in a forward direction, as is the case with vertebrates and insects.

Some members of the sea urchin family have hoof-like formations on the ends of some of their spines, with which they are enabled to walk over the sea bottom without using the suction disks. About the only enemy of these fearsome nightmares of the deep is man. Some species are used extensively for human food, notably among the Mediterranean coast and in the West Indies. The developing eggs are taken from the body and eaten either raw or cooked. Even if it should prove suitable for human food, it is unlikely that the sea porcupine ever will be a rival in this respect of its rival, the “sea rabbit.” It is too secluded in its habitat.

Worms That Are Unkillable

In nematodes life may have reached its greatest capacity for survival. The remarkable persistence of these soil worms has been studied by C. W. McBeth, researcher of the Shell Oil Company. One form, he reports, has been known to survive after 25 years in a glass bottle in a laboratory. Another, a pest of wheat kernels, apparently came back to life after 28 years in laboratory storage. A nematode which had invaded a rye plant, collected in Kansas in 1906, revived after 39 years of complete dehydration in a herbarium.

Those which live as active feeders in the soil, however, are not particularly long-lived. Each species depends on a certain plant type and must starve if this is not available. The recently introduced golden nematode of potatoes, a particularly obnoxious pest, is known, however, to survive as much as ten years in soils where no potatoes are planted. A great mass of eggs is produced, but not laid. They are retained in the body of the mother, who dies. Her skin remains—a bag filled with eggs.

This stays in the soil, apparently unharmed by changing conditions, until potatoes are planted again. Then some mysterious influence, as yet unexplained, causes the eggs to hatch and the whole nematode cycle begins once more.