IV. The Rim of Sand 4 страница

But if this area has little life within itself, it is full of the reminders of other lives. For here above the high‑tide line, all the empty shells of the mollusks come to rest. Visiting the beach that borders Shackleford Shoals in North Carolina or Florida’s Sanibel Island, one could almost believe that mollusks are the only inhabitants of the sea’s edge, for their enduring remains dominate the beach debris long after the more fragile remnants of crabs and sea urchins and starfish have been returned to the elements. First the shells were dropped low on the beach by the waves; then, tide by tide, they were moved up across the sands to the line of the highest of the high tides. Here they will remain, till buried in drifting sand or carried away in a wild carnival of storm surf.

From north to south the composition of the shell windrows changes, reflecting the changing communities of the mollusks. Every little pocket of gravelly sand that accumulates in favorable spots amid the rocks of northern New England is strewn with mussels and periwinkles. And when I think of the sheltered beaches of Cape Cod I see in memory the windrows of jingle shells being shifted gently by the tide, their thin, scale‑like valves (how can they house a living creature?) gleaming with a satin sheen. The arched upper valve occurs more often in beach flotsam than the flat lower one, which is perforated by a hole for the passage of the strong byssus cord that attaches the jingle to a rock or to another shell. Silver, gold, and apricot are the colors of the jingles, set against the deep blue of the mussels that dominate these northern shores. And scattered here and there are the ribbed fans of the scallops and the little white sloops of the boat shells stranded on the beach. The boat shell is a snail with a curiously modified shell, having a little “half deck” on the lower surface. It often becomes attached to its fellows in chains of half a dozen or more individuals. Each boat shell is in its lifetime first male then female. In the chains of attached shells those at the bottom of the chain are always females, the upper animals males.

On the Jersey beaches and the coastal islands of Maryland and Virginia the massive structure of the shells and the lack of ornamental spines have a meaning–that the offshore world of shifting sand is deeply stirred by the endless processions of the waves that roll in on this coast. The thick shell of the surf clam is its defense against the force of the waves. These shores are strewn, too, with the heavy armaments of the whelks, and with the smooth globes of the moon snails.

From the Carolinas south the beach world seems to belong to the several species of arks, whose shells outnumber all others. Though variously shaped, their shells are stout, with long straight hinges. The ponderous ark wears a black, beardlike growth, or periostracum, heavy in fresh specimens, scanty or absent in beach‑worn shells. The turkey wing is a gaily colored ark, with reddish bands streaking its yellowish shell. It, too, wears a thick periostracum, and lives down in deep offshore crevices, where it attaches itself to rocks or any other support by a strong line or byssus. While a few kinds of arks extend the range of these mollusks throughout New England (for example, the small transverse ark and the so‑called bloody clam–one of the few mollusks that has red blood) it is on southern beaches that the group becomes dominant. On famed Sanibel Island on the west coast of Florida, where the variety of shells is probably greater than anywhere else on our Atlantic coast, the arks nevertheless make up about 95 per cent of the beach deposits.

The pen shells begin to appear in numbers on the beaches below Capes Hatteras and Lookout, but perhaps they, too, live in the most prodigious numbers on the Gulf coast of Florida. I have seen truckloads of them on the beach at Sanibel even in calm winter weather. In a violent tropical hurricane the destruction of this light‑shelled mollusk is almost incredible. Sanibel Island presents about fifteen miles of beach to the Gulf of Mexico. On this strand, it has been estimated, about a million pen shells have been hurled by a single storm, having been torn loose by waves reaching down to bottoms lying as deep as 30 feet. The fragile shells of the pens are ground together in the buffeting of storm surf; many are broken, but even those not so destroyed have no way of returning to the sea, and so are doomed. As if knowing this, the commensal pea crabs that inhabit them creep out of the shells like the proverbial rats abandoning a sinking ship; they may be seen by the thousand swimming about in apparent bewilderment in the surf.

The pen shells spin anchoring byssus threads of golden sheen and remarkable texture; the ancients spun their cloth of gold from the byssus of the Mediterranean pens, producing a fabric so line and soft it could be drawn through a finger ring. The industry persists at Italian Taranto, on the Ionian Sea, where gloves and other small garments are woven of this natural fabric as curios or tourists’ souvenirs.

The survival of an undamaged angel wing in the debris of the upper beach seems extraordinary, so delicately fragile does it appear. Yet these valves of purest white, when worn by the living animals, are capable of penetrating peat or firm clay. The angel wing is one of the most powerful of the boring clams and, having very long siphons with which to maintain communication with the sea water, is able to burrow deeply. I have dug for them in peat beds in Buzzards Bay, and have found them on beach exposures of peat on the coast of New Jersey, but their occurrence north of Virginia is local and rare.

This purity of color, this delicacy of structure are buried throughout life in a bank of clay, for the angel wing’s beauty seems destined to be hidden from view until, after the death of the animal, the shells are released by the waves and carried to the beach. In its dark prison the angel wing conceals an even more mysterious beauty. Secure from enemies, hidden from all other creatures, the animal itself glows with a strange green light. Why? For whose eyes? For what reason?

Besides the shells, there are other objects in the beach flotsam that are mysterious in shape and texture. Flat, horny or shell‑like discs of various shapes and sizes are the opercula of sea snails–the protective doors that close over the opening when the animal has withdrawn into its shell. Some opercula are round, some leaf‑shaped, some like slender, curving daggers. (The “cat’s eye” of the South Pacific is the operculum of a snail, rounded on one surface and polished like a boy’s marble.) The opercula of the various species are so characteristic in shape, material, and structure that they are a useful means of identifying otherwise difficult species.

The tidal flotsam abounds, too, in many little empty egg cases in which various sea creatures passed their first days of life. These are of various shapes and materials. The black “mermaid’s purses” belong to one of the skates. They are flat, horny rectangles, with two long, curling prongs or tendrils extending from each end. With these the parent skate attaches the packet containing a fertilized egg to seaweeds on some offshore bottom. After the young skate matures and hatches, its discarded cradle is often washed up on the beach. Egg cases of the banded tulip shell remind one of the dried seed pods of a flower, a cluster of thin, parchment‑like containers borne on a central stalk. Those of the channeled or the knobbed whelks are long, spiraling strings of little capsules, again parchment‑like in texture. Each of the flat, ovoid capsules contains scores of baby whelks, incredible in the minute perfection of their shells. Sometimes a few remain in an egg string found on the beach; they rattle against the hard walls of the capsule like peas in a dried pod.

Perhaps the most baffling of all objects found on beaches are the egg cases of the sand collar snail or moon snail. If someone had cut a doll’s shoulder cape out of a piece of fine sandpaper, the result would be about the same. The “collars” produced by the various species of the family of moon snails differ in size and, though slightly, in shape. In some the edges are smooth, in others scalloped. The arrangement of the eggs also follows slightly different patterns in the various species. This strange receptacle for the eggs of the snail is formed as a sheet of mucus pushed out from under the foot and molded on the outside of the shell. This results in the collar shape. The eggs are attached to the under side of the collar, which becomes completely impregnated with sand grains.

Mingled with the bits and fragments of sea creatures are the reminders of man’s invasion of the sea–spars, pieces of rope, bottles, barrels, boxes of many shapes and sizes. If these have been long at sea, they bring their own collection of sea life, for in their period of drifting in the currents, they have served as a solid place of attachment for the searching larvae of the plankton.

On our Atlantic coast, the days following a northeast blow or a tropical storm are a time to look for the driftage of open ocean. I remember such a day on the beach at Nags Head, after a hurricane had passed by at sea during the night. The wind was still blowing a gale; there was a fine wild surf. That day the beach was strewn with many bits of driftwood, branches of trees, and heavy planks and spars, many of which bore growths of Lepas, the gooseneck barnacle of the open sea. One long plank was studded with tiny barnacles the size of a mouse’s ear; on some of the other drifted timbers the barnacles had grown to a length of an inch or more, exclusive of the stalk. The size of the encrusting barnacles is a rough index of the time the spar has been at sea. In the profusion of their growth on almost every piece of timber one senses the incredible abundance of barnacle larvae drifting in the sea, ready to grasp any firm object adrift in their fluid world, for by strange irony none of them could complete their development in the sea water alone. Each of those weird‑looking little beings, rowing through the water with feathered appendages, had to find a hard surface to which it could attach before assuming the adult form.

The life history of these stalked barnacles is very similar to that of the acorn barnacles of the rocks. Within the hard shells is a small crustacean body, bearing feathered appendages with which to sweep food into their mouths. The chief difference is that the shells are borne on a fleshy stalk instead of arising from a flat base firmly cemented to the substratum. When the animals are not feeding, the shells can be tightly closed, as in the rock barnacle; when they open to feed, there are the same sweeping, rhythmical motions of the appendages.

Seeing on the shore a branch from some tree that evidently has been long adrift and now is generously sprinkled with the fleshy brown stalks and the ivory‑hued shells of the barnacle, with their marginal tints of blue and red, one can remember with tolerant understanding the old medieval misconception that conferred on these strange crustaceans the name “goose barnacle.” The seventeenth‑century English botanist John Gerard compiled a description of the “goose tree” or “Barnakle tree” on the basis of the following experience: “Traveling upon the shores of our English coast between Dover and Rummey, I founde the trunke of an olde rotten tree, which … we drewe out of the water upon dry lande; on this rotten tree I founde growing many thousands of long crimson bladders … at the neather end whereof did grow a shell fish, fashioned somewhat like a small Muskle … which after I had opened … I found living things that were very naked, in shape like a Birde; in others, the Birde covered with soft downe, the shell halfe open, and the Birde readie to fall out, which no doubt were the foules called Barnakles.” Evidently Gerard’s imaginative eye saw in the appendages of the barnacles the resemblance to a bird’s feathers. On this slender basis he built the following pure fabrication: “They spawne as it were in March and April; the Geese are formed in Maie and June, and come to fulnesse of feathers in the moneth after.” And so in many an old work of un‑natural history from this time on, we see drawings of trees bearing fruit in the form of barnacles, and geese emerging from the shells to fly away.

Old spars and water‑soaked timbers cast on the beach are full of the workings of the shipworm–long cylindrical tunnels penetrating all parts of the wood. Usually nothing remains of the creatures themselves except occasional fragments of their small calcareous shells; these proclaim that the shipworm is a true mollusk, despite its long, slender, and wormlike body.

There were shipworms long before there were men; yet within his own short tenancy of earth, man has greatly increased their numbers. The shipworm can live only in wood; if its young fail to discover some woody substance at a critical period of their existence, they die. This absolute dependence of a sea creature on something derived from the continents seems strange and incongruous. There could have been no shipworms until woody plants evolved on land. Their ancestors probably were clamlike forms burrowing in mud or clay, merely using their excavated holes as a base from which to extract the plankton of the sea. Then after trees evolved, these forerunners of the shipworms adapted themselves to a new habitat–the relatively few forest trees brought into the sea by rivers. But their numbers over all the earth must have been small until, scant thousands of years ago, men began to send wooden vessels across the sea and to build wharves at its edge; in all such wooden structures, the shipworm found a greatly extended range, to the cost of the human race.

The shipworm’s place in history is secure. It was the scourge of the Romans with their galleys, of the seagoing Greeks arid Phoenicians, of the explorers of the New World. In the 1700’s it riddled the dikes that the Dutch had built to keep out the sea; by so doing it threatened the very life of Holland. (As an academic by‑product, the first extensive studies of the shipworm were made by Dutch scientists, to whom knowledge of its biology had become a matter of life and death. Snellius, in 1733, pointed out for the first time that this animal is a clamlike mollusk, not a worm.) About 1917 the shipworm invaded the harbor of San Francisco. Before its inroads were even suspected, ferry slips had begun to collapse, and wharves and loaded freight cars fell into the harbor. During the Second World War, especially in all tropical waters, the shipworm was an unseen but powerful enemy.

The female of the common shipworm retains the young in her burrow until they have attained the larval stage. Then they are launched into the sea–each a tiny being enclosed in two protective shells, looking like any other young bivalve. If it encounters wood when it has reached the threshold of adulthood, all goes well. It puts out a slender byssus thread as an anchor, a foot develops, and the shells become modified into efficient cutting tools, for rows of sharp ridges appear on their outer surfaces. The burrowing begins. With a powerful muscle, the animal scrapes the ridged shell against the wood, revolving meanwhile so that a smooth, cylindrical burrow is cut. As the burrow is extended, usually with the grain of the wood, the body of the shipworm grows. One end remains attached to the wall near the tiny point of entrance. This bears the siphons through which contact with the sea is maintained. The penetrating end carries the small shells. Between stretches a body that is thin as a lead pencil, but may reach a length of eighteen inches. Although a timber may be infested with hundreds of larvae, the burrows of the shipworms never interfere with each other. If an animal finds itself coming close to another burrow, it invariably turns aside. As it bores, it passes the loosened fragments of wood through its digestive tract. Some of the wood is digested and converted into glucose. This ability to digest cellulose is rare in the animal world–only certain snails, certain insects, and a very few others possess it. But the shipworm makes little use of this difficult art, and feeds chiefly on the rich plankton streaming through its body.

Other timbers on the beach bear the marks of the wood piddock. These are shallow holes that penetrate only the outer portions just beneath the bark, but they are broad and cleanly cylindrical. The boring piddock is seeking only shelter and protection. Unlike the shipworm, it does not digest the wood, but lives only on the plankton that it draws into its body through a protruding siphon.

Empty piddock holes sometimes attract other lodgers, as abandoned birds’ nests may become homes for insects. On the muddy banks of salt creeks at Bears Bluff in South Carolina, I have picked up timbers riddled with holes. Once stout little white‑shelled piddocks dwelt in them. The piddocks were long since dead and even the shells were gone, but in each hole was a dark glistening body like a raisin embedded in a cake. They were the contracted tissues of small anemones, finding there, in this world of silt‑laden water and yielding mud, that bit of firm foundation which anemones must have. Seeing anemones in such an improbable place, one wonders how the larvae happened to be there, ready to seize the chance opportunity presented by that timber with its neatly excavated apartments; and one is struck anew by the enormous waste of life, remembering that for each of these anemones that succeeded in finding a home, many thousands must have failed.

Always, then, in this flotsam and jetsam of the tide lines, we are reminded that a strange and different world lies offshore. Though what we see here may be but the husks and fragments of life, through it we are made aware of life and death, of movement and change, of the transport of living things by ocean currents, by tides, by wind‑driven waves. Some of these involuntary migrants are adults. They may perish in mid‑journey; a few, being transported into a new home and finding there conditions that are favorable, may survive, may even produce surviving young to extend the range of the species. But many others are larvae, and whether or not they will make a successful landing depends on many things–on the length of their larval life (can they wait for a distant landfall before they reach the stage when they must take up an adult existence?)–on the temperature of the water they encounter–on the set of the currents that may carry them to favoring shoals, or off into deep water where they will be lost.

And so, walking the beach, we become aware of a most fascinating problem–the colonization of the shore, and especially of those “islands” of rock (or the semblance of rock) that occur in the midst of a sea of sand. For whenever a seawall is built, or a jetty, or pilings are sunk for a pier or a bridge, or rock, long hidden from sun and buried even beneath the sea, emerges again on the ocean floor, these hard surfaces immediately become peopled with typical animals of the rocks. But how did the colonizing rock fauna happen to be at hand–here in the midst of a sandy coast that stretches for hundreds of miles to north and south?

Pondering the answer, we become aware of that ceaseless migration, for the most part doomed to futility, yet ensuring that always, when opportunity arises, Life shall be waiting, ready to take advantage. For the ocean currents are not merely a movement of water; they are a stream of life, carrying always the eggs and young of countless sea creatures. They have carried the hardier ones across oceans, or step by step on long coastwise journeys. They have carried some along deep, hidden passageways where cold currents flow along the floor of the ocean. They have brought inhabitants to populate new islands pushing above the surface of the sea. These things they have done, we must suppose, since first there was life in the sea.

And as long as the currents move on their courses there is the possibility, the probability, even the certainty, that some particular form of life will extend its range, will come to occupy new territory.

As almost nothing else does, this to me expresses the pressure of the life force–the intense, blind, unconscious will to survive, to push on, to expand. It is one of life’s mysteries that most of the participants in this cosmic migration are doomed to failure; it is no less mysterious that their failure turns into success when, for all the billions lost, a few succeed.