In the North Atlantic ship lanes the same play is staged with different actors. Instead of the equatorial currents there are the Gulf Stream and its continuation, the North Atlantic Drift, and the Arctic Current; instead of confused swell and squalls of rain there are slicks and fogs. Tropicbirds are replaced by jaegers and skuas; and different species of the petrel group, usually here spoken of as shearwaters and fulmars, are flying or swimming about, often in great flocks … Here, too, perhaps, one sees less of sharks and more of porpoise racing with the cut-water or doggedly hurrying, school after school, toward some unguessable objective. The flashing black and white of the young orcas, or the distant sudden spurt and lazy drift of a whale’s spouting, lend life to the water, as do the antics of flying fish, distant though they be from their traditional home in the tropics … One may pass from the blue water of the Stream, with floating gulf weed (Sargassum), and perhaps here and there the iridescent float of a Portuguese man-of-war, into the gray-green water of the Arctic Current with its thousands of jelly fish, and in a few hours back again into the Stream. Each time, at the margin, one is likely to see the surface display of that abundance of life which has made the Grand Banks one of the great fisheries of the world.*
The mid-ocean regions, bounded by the currents that sweep around the ocean basins, are in general the deserts of the sea. There are few birds and few surface-feeding fishes, and indeed there is little surface plankton to attract them. The life of these regions is largely confined to deep water. The Sargasso Sea is an exception, not matched in the anticyclonic centers of other ocean basins. It is so different from any other place on earth that it may well be considered a definite geographic region. A line drawn from the mouth of Chesapeake Bay to Gibraltar would skirt its northern border; another from Haiti to Dakar would mark its southern boundary. It lies all about Bermuda and extends more than half-way across the Atlantic, its entire area being roughly as large as the United States. The Sargasso, with all its legendary terrors for sailing ships, is a creation of the great currents of the North Atlantic that encircle it and bring into it the millions of tons of floating sargassum weed from which the place derives its name, and all the weird assemblage of animals that live in the weed.
The Sargasso is a place forgotten by the winds, undisturbed by the strong flow of waters that girdle it as with a river. Under the seldom-clouded skies, its waters are warm and heavy with salt. Separated widely from coastal rivers and from polar ice, there is no inflow of fresh water to dilute its saltiness; the only influx is of saline water from the adjacent currents, especially from the Gulf Stream or North Atlantic Current as it crosses from America to Europe. And with the little, inflowing streams of surface water come the plants and animals that for months or years have drifted in the Gulf Stream.
The sargassum weeds are brown algae belonging to several species. Quantities of the weeds live attached to reefs or rocky outcroppings off the coasts of the West Indies and Florida. Many of the plants are torn away by storms, especially during the hurricane season. They are picked up by the Gulf Stream and are drifted northward. With the weeds go, as involuntary passengers, many small fishes, crabs, shrimps, and innumerable larvae of assorted species of marine creatures, whose home had been the coastal banks of sargassum weed.
Curious things happen to the animals that have ridden on the sargassum weed into a new home. Once they lived near the sea’s edge, a few feet or a few fathoms below the surface, but never far above a firm bottom. They knew the rhythmic movements of waves and tides. They could leave the shelter of the weeds at will and creep or swim about over the bottom in search of food. Now, in the middle of the ocean, they are in a new world. The bottom lies two or three miles below them. Those who are poor swimmers must cling to the weed, which now represents a life raft, supporting them above the abyss. Over the ages since their ancestors came here, some species have developed special organs of attachment, either for themselves or for their eggs, so that they may not sink into the cold, dark water far below. The flying fish make nests of the weed to contain their eggs, which bear an amazing resemblance to the sargassum floats or ‘berries.’
Indeed, many of the little marine beasts of the weedy jungle seem to be playing an elaborate game of disguise in which each is camouflaged to hide it from the others. The Sargasso sea slug—a snail without a shell—has a soft, shapeless brown body spotted with dark-edged circles and fringed with flaps and folds of skin, so that as it creeps over the weed in search of prey it can scarcely be distinguished from the vegetation. One of the fiercest carnivores of the place, the sargassum fish Pterophryne, has copied with utmost fidelity the branching fronds of the weed, its golden berries, its rich brown color, and even the white dots of encrusting worm tubes. All these elaborate bits of mimicry are indications of the fierce internecine wars of the Sargasso jungles, which go on without quarter and without mercy for the weak or the unwary.
In the science of the sea there has been a long-standing controversy about the origin of the drifting weeds of the Sargasso Sea. Some have held that the supply is maintained by weeds recently torn away from coastal beds; others say that the rather limited sargassum fields of the West Indies and Florida cannot possibly supply the immense area of the Sargasso. They believe that we find here a self-perpetuating community of plants that have become adapted to life in the open sea, needing no roots or holdfasts for attachment, and able to propagate vegetatively. Probably there is truth in both ideas. New plants do come in each year in small numbers, and now cover an immense area because of their very long life once they have reached this quiet central region of the Atlantic.
It takes about half a year for the plant’s torn from West Indian shores to reach the northern border of the Sargasso, perhaps several years for them to be carried into the inner parts of this area. Meanwhile, some have been swept onto the shores of North America by storms, others have been killed by cold during the passage from offshore New England across the Atlantic, where the Gulf Stream comes into contact with waters from the Arctic. For the plants that reach the calm of the Sargasso, there is virtual immortality. A. E. Parr of the American Museum has recently suggested that the individual plants may live, some for decades, others for centuries, according to their species. It might well be that some of the very weeds you would see if you visited the place today were seen by Columbus and his men. Here, in the heart of the Atlantic, the weed drifts endlessly, growing, reproducing vegetatively by a process of fragmentation. Apparently almost the only plants that die are the ones that drift into unfavorable conditions around the edges of the Sargasso or are picked up by outward-moving currents.
Such losses are balanced, or possibly a little more than balanced, by the annual addition of weeds from distant coasts. It must have taken eons of time to accumulate the present enormous quantities of weed, which Parr estimates as about 10 million tons. But this, of course, is distributed over so large an area that most of the Sargasso is open water. The dense fields of weeds waiting to entrap a vessel never existed except in the imaginations of sailors, and the gloomy hulks of vessels doomed to endless drifting in the clinging weed are only the ghosts of things that never were.
* From The Condor, vol. 36, no. 5, Sept.–Oct. 1934, pp. 186–7.
The Changing Year
Thus with the year seasons return.
MILTON
FOR THE SEA AS a whole, the alternation of day and night, the passage of the seasons, the procession of the years, are lost in its vastness, obliterated in its own changeless eternity. But the surface waters are different. The face of the sea is always changing. Crossed by colors, lights, and moving shadows, sparkling in the sun, mysterious in the twilight, its aspects and its moods vary hour by hour. The surface waters move with the tides, stir to the breath of the winds, and rise and fall to the endless, hurrying forms of the waves. Most of all, they change with the advance of the seasons. Spring moves over the temperate lands of our Northern Hemisphere in a tide of new life, of pushing green shoots and unfolding buds,
all its mysteries and meanings symbolized in the northward migration of the birds, the awakening of sluggish amphibian life as the chorus of frogs rises again from the wet lands, the different sound of the wind stirs the young leaves where a month ago it rattled the bare branches. These things we associate with the land, and it is easy to suppose that at sea there could be no such feeling of advancing spring. But the signs are there, and seen with understanding eye, they bring the same magical sense of awakening.
In the sea, as on land, spring is a time for the renewal of life. During the long months of winter in the temperate zones the surface waters have been absorbing the cold. Now the heavy water begins to sink, slipping down and displacing the warmer layers below. Rich stores of minerals have been accumulating on the floor of the continental shelf—some freighted down the rivers from the lands; some derived from sea creatures that have died and whose remains have drifted down to the bottom; some from the shells that once encased a diatom, the streaming protoplasm of a radiolarian, or the transparent tissues of a pteropod. Nothing is wasted in the sea; every particle of material is used over and over again, first by one creature, then by another. And when in spring the waters are deeply stirred, the warm bottom water brings to the surface a rich supply of minerals, ready for use by new forms of life.
Just as land plants depend on minerals in the soil for their growth, every marine plant, even the smallest, is dependent upon the nutrient salts or minerals in the sea water. Diatoms must have silica, the element of which their fragile shells are fashioned. For these and all other microplants, phosphorus is an indispensable mineral. Some of these elements are in short supply and in winter may be reduced below the minimum necessary for growth. The diatom population must tide itself over this season as best it can. It faces a stark problem of survival, with no opportunity to increase, a problem of keeping alive the spark of life by forming tough protective spores against the stringency of winter, a matter of existing in a dormant state in which no demands shall be made on an environment that already withholds all but the most meager necessities of life. So the diatoms hold their place in the winter sea, like seeds of wheat in a field under snow and ice, the seeds from which the spring growth will come.
These, then, are the elements of the vernal blooming of the sea: the ‘seeds’ of the dormant plants, the fertilizing chemicals, the warmth of the spring sun.
In a sudden awakening, incredible in its swiftness, the simplest plants of the sea begin to multiply. Their increase is of astronomical proportions. The spring sea belongs at first to the diatoms and to all the other microscopic plant life of the plankton. In the fierce intensity of their growth they cover vast areas of ocean with a living blanket of their cells. Mile after mile of water may appear red or brown or green, the whole surface taking on the color of the infinitesimal grains of pigment contained in each of the plant cells.
The plants have undisputed sway in the sea for only a short time. Almost at once their own burst of multiplication is matched by a similar increase in the small animals of the plankton. It is the spawning time of the copepod and the glassworm, the pelagic shrimp and the winged snail. Hungry swarms of these little beasts of the plankton roam through the waters, feeding on the abundant plants and themselves falling prey to larger creatures. Now in the spring the surface waters become a vast nursery. From the hills and valleys of the continent’s edge lying far below, and from the scattered shoals and banks, the eggs or young of many of the bottom animals rise to the surface of the sea. Even those which, in their maturity, will sink down to a sedentary life on the bottom, spend the first weeks of life as freely swimming hunters of the plankton. So as spring progresses new batches of larvae rise into the surface each day, the young of fishes and crabs and mussels and tube worms, mingling for a time with the regular members of the plankton.
Under the steady and voracious grazing, the grasslands of the surface are soon depleted. The diatoms become more and more scarce, and with them the other simple plants. Still there are brief explosions of one or another form, when in a sudden orgy of cell division it comes to claim whole areas of the sea for its own. So, for a time each spring, the waters may become blotched with brown, jellylike masses, and the fishermen’s nets come up dripping a brown slime and containing no fish, for the herring have turned away from these waters as though in loathing of the viscid, foul-smelling algae. But in less time than passes between the full moon and the new, the spring flowering of Phaeocystis is past and the waters have cleared again.
In the spring the sea is filled with migrating fishes, some of them bound for the mouths of great rivers, which they will ascend to deposit their spawn. Such are the spring-run chinooks coming in from the deep Pacific feeding grounds to breast the rolling flood of the Columbia, the shad moving into the Chesapeake and the Hudson and the Connecticut, the alewives seeking a hundred coastal streams of New England, the salmon feeling their way to the Penobscot and the Kennebec. For months or years these fish have known only the vast spaces of the ocean. Now the spring sea and the maturing of their own bodies lead them back to the rivers of their birth.
Other mysterious comings and goings are linked with the advance of the year. Capelin gather in the deep, cold water of the Barents Sea, their shoals followed and preyed upon by flocks of auks, fulmars, and kittiwakes. Cod approach the banks of Lofoten, and gather off the shores of Ireland. Birds whose winter feeding territory may have encompassed the whole Atlantic or the whole Pacific converge upon some small island, the entire breeding population arriving within the space of a few days. Whales suddenly appear off the slopes of the coastal banks where the swarms of shrimplike krill are spawning, the whales having come from no one knows where, by no one knows what route.
With the subsiding of the diatoms and the completed spawning of many of the plankton animals and most of the fish, life in the surface waters slackens to the slower pace of midsummer. Along the meeting places of the currents the pale moon jelly Aurelia gathers in thousands, forming sinuous lines or windrows across miles of sea, and the birds see their pale forms shimmering deep down in the green water. By midsummer the large red jellyfish Cyanea may have grown from the size of a thimble to that of an umbrella. The great jellyfish moves through the sea with rhythmic pulsations, trailing long tentacles and as likely as not shepherding a little group of young cod or haddock, which find shelter under its bell and travel with it.
A hard, brilliant, coruscating phosphorescence often illuminates the summer sea. In waters where the protozoa Noctiluca is abundant it is the chief source of this summer luminescence, causing fishes, squids, or dolphins to fill the water with racing flames and to clothe themselves in a ghostly radiance. Or again the summer sea may glitter with a thousand thousand moving pinpricks of light, like an immense swarm of fireflies moving through a dark wood. Such an effect is produced by a shoal of the brilliantly phosphorescent shrimp Meganyctiphanes, a creature of cold and darkness and of the places where icy water rolls upward from the depths and bubbles with white ripplings at the surface.
Out over the plankton meadows of the North Atlantic the dry twitter of the phalaropes, small brown birds, wheeling and turning, dipping and rising, is heard for the first time since early spring. The phalaropes have nested on the arctic tundras, reared their young, and now the first of them are returning to the sea. Most of them will continue south over the open water far from land, crossing the equator into the South Atlantic. Here they will follow where the great whales lead, for where the whales are, there also are the swarms of plankton on which these strange little birds grow fat.
As the fall advances, there are other movements, some in the surface, some hidden in the green depths, that betoken the end of summer. In the fog-covered waters of Bering Sea, down through the treacherous passes between the islands of the Aleutian chain and southward into the open Pacific, the herds of fur seals are moving. Left behind are two small islands, treeless bits of volcanic soil thrust up into the waters of Bering Sea. The islands are silent now, but for th
e several months of summer they resounded with the roar of millions of seals come ashore to bear and rear their young—all the fur seals of the eastern Pacific crowded into a few square miles of bare rock and crumbling soil. Now once more the seals turn south, to roam down along the sheer underwater cliffs of the continent’s edge, where the rocky foundations fall away steeply into the deep sea. Here, in a blackness more absolute than that of arctic winter, the seals will find rich feeding as they swim down to prey on the fishes of this region of darkness.
Autumn comes to the sea with a fresh blaze of phosphorescence, when every wave crest is aflame. Here and there the whole surface may glow with sheets of cold fire, while below schools of fish pour through the water like molten metal. Often the autumnal phosphorescence is caused by a fall flowering of the dinoflagellates, multiplying furiously in a short-lived repetition of their vernal blooming.
Sometimes the meaning of the glowing water is ominous. Off the Pacific coast of North America, it may mean that the sea is filled with the dinoflagellate Gonyaulax, a minute plant that contains a poison of strange and terrible virulence. About four days after Gonyaulax comes to dominate the coastal plankton, some of the fishes and shellfish in the vicinity become toxic. This is because, in their normal feeding, they have strained the poisonous plankton out of the water. Mussels accumulate the Gonyaulax toxins in their livers, and the toxins react on the human nervous system with an effect similar to that of strychnine. Because of these facts, it is generally understood along the Pacific coast that it is unwise to eat shellfish taken from coasts exposed to the open sea when Gonyaulax may be abundant, in summer or early fall. For generations before the white men came, the Indians knew this. As soon as the red streaks appeared in the sea and the waves began to flicker at night with the mysterious blue-green fires, the tribal leaders forbade the taking of mussels until these warning signals should have passed. They even set guards at intervals along the beaches to warn inlanders who might come down for shellfish and be unable to read the language of the sea.