The mighty deep

CORAL is a familiar enough object with us all, whether in the shape of a child’s first plaything, or a girl’s first trinket, or a Museum curiosity. It may be red or pink or white; it may be polished into smoothness or left in its natural state of jagged roughness, dotted over with tiny pits. In any case, it is a thing of interest and beauty. In any case, it is the dead skeleton of a once-living animal.

In the Red Sea alone about one hundred and twenty kinds of Coral are found, and in Ocean waters the numbers rise rapidly.

Perhaps one of the species best known to us is the small red coral of the Mediterranean, usually gathered from shallow parts, though sometimes fished up from a thousand feet deep.

This kind seldom exceeds ten or twelve inches in length; and when alive, the pretty branching skeleton is clothed in a thin tinted jelly-like vesture, which, though in a sense one, is yet no “single individual.” It is formed of many polyps, all united together, while each has its own separate mouth, and each holds out its own tiny feelers for food. Once let the branch be taken from the water, and only one result can follow. Life quickly fades; the enfolding vesture disappears; and a bare red skeleton is left for use in the market, to be made into toy or ornament.

The word Coral has other associations. It carries our thoughts far from home to fair isles in tropical seas—isles connected in our memories with tales of shipwrecked mariners and hair-breadth escapes, of dashing waves and peaceful lagoons, of breadfruit trees and waving palms, of perpetual sunshine and endless holidays, of Robinson Crusoe adventures and interesting islanders, of poisoned arrows and ferocious sharks.

Such islands do exist, and in numbers far greater than we commonly realise.

At this moment I have before me a map of the world, made for the express purpose of showing “Coral Seas,” or the regions where Coral islands are constructed. And the red patches are astonishingly plentiful, dotting a broad belt of ocean all round the world, except where that belt is interrupted by Continents, within the limits, roughly, of 30° north latitude and 30° south latitude.

In the West Indies coral islands abound. Travelling westward from America we come across the same material, in extensive regions to the north-east, the north, and the north-west of Australia. Tahiti, Samoa, the Fijis, the Solomons, the New Hebrides, the Carolines, the Marshall Islands, the Seychelles, and innumerable others, are literally made of coral.

Not made as sandstone and chalk are made, put together by the slow action of the sea, far below the surface. This is another kind of making.

Coral is built by living creatures, near the surface of the water. All that the waves have to do is, firstly, to bring abundance of food to the polyps, when alive, since by reason of their ponderous rock-skeletons they cannot go in search of food; and secondly, after the death of the polyps, to break and grind and heap together the skeleton-remains.

We have seen something of ocean “stone-makers,” in the story of Chalk. Here we have the same thing again. As the tiny shells, which go to the building of chalk, are the dead remains of once-living jelly-specks, so these great masses of coral, forming islands and reefs in southern seas, are largely the skeletons of once-living polyps.

A coral-polyp, like a jelly-speck, has power to take lime from sea-water. It has power to secrete carbonate-of-lime. It has power to deposit that carbonate-of-lime in solid masses.

But whereas the jelly-speck lives inside its shell, putting out tiny temporary limbs through holes for food, the coral-polyp more often lives outside its skeleton, clothing the dry bones with translucent jelly. This is rather more after the fashion in which man clothes his skeleton. Yet because of its make the coral-polyp cannot properly, in the full sense of the word, “secrete” or hide its internal framework.

It is hardly fair to speak of “the polyp” and of “it” in this connection. “Polyps” and “they” are more correct.

For the coral-polyps live in close communities, in very near fellowship, acting on co-operative principles of the most advanced kind. Each individual may, it is true, have its own mouth, its own tentacles, and even its own small stomach. But the latter at least can hardly be reckoned as personal property, since all are so connected that liquids pass freely from one to another, and the food which is taken in by one polyp helps to nourish its neighbours.

And again, while we speak of coral as being “built,” that really is not the right word; unless we may also talk of the “building” of a man’s skeleton, or of an elephant’s framework.

“Built” undeniably it is; but the building implies no conscious effort, no deliberate intention, no praiseworthy exertions, on the part of the builder. Coral is simply “secreted”—is unknowingly and without choice put together by the polyps.

There is invention; there is plan; there is design. But these belong to a Mind, above and beyond and out of sight; not in anywise to the live jelly which clothes the coral-skeleton, or to the extremely limited understanding of that co-operative jelly-sheet.

Not all polyps have stony skeletons. On our sea-shores we have species many, and individuals by tens of thousands, which secrete no coral. They are known to us as Sea-Anemones: and the first-cousins of these dainty flower-like beings, inhabiting British salt-pools, construct miles and miles of coral far off in southern seas.

Some few even among coral-polyps live individual lives, but the greater number follow the community-system. This must always be looked upon as an inferior way of existence.

The most usual way in which polyps increase is by “budding”—not unlike the growth of a plant by buds. A small lump appears on one side of the parent, which increases fast in size, develops a mouth and tentacles, and by-and-by gives birth itself to other buds. The increase of numbers is enormous. One polyp may produce in a short time thousands or even tens of thousands of descendants.

But in the case of coral-polyps the children do not leave the parents or go out into the world. They cling to the old stock; they partake of the united family-life; and each little mouth and stomach works for the benefit of all the little stomachs of the whole community.

Some polyps, instead of budding like a plant, increase by division. One polyp separates into two parts, each of which becomes a full-grown animal; and each then divides anew; this plan continuing ad infinitum. Here again the growth of numbers is not slow.

Occasionally, in place of spreading in branch-like shapes, they grow in solid rounded masses. Such a sphere-like mass in tropical waters of the Pacific may be twenty feet in diameter—one huge family of united beings, each perhaps under a twentieth of an inch across, and all together clothing a skeleton common to the entire clan.

In these cases the tips of the branches or the outer edges of the rounded mass are the young polyps, while the older ones lie lower down or more inward.

As the tree or ball of coral grows, spreading farther, giving birth to fresh generations of polyps, the old ones die off. So the living and the dead are found in one community, in close touch, on a single branch or a single mound of coral. At the tip of each twig may be the brightly-coloured active jelly, while the stem below is a dead skeleton. On a solid mass of coral, twenty feet in diameter, the whole outside may be alive, down perhaps to a depth of half-an-inch, while the whole inside is lifeless bone. That is how the coral grows.

Living coral is seldom found at any greater depth in the sea than about twenty fathoms, and the limits of temperature which the polyps can endure are narrow. Their growth is quickly checked by water a little too deep or a little too cold, and by water not very pure. Abundance of lime also is needful.

An “atoll” is a coral-reef standing alone, generally of a round or oval shape, with a lake of calm sea-water in its centre, while ocean-billows thunder on the outer margin. The polyps love those waves; but they fade and die in the inclosed lagoon, where the water is not often enough renewed to supply them with food.

Much the same in make are the Fringing Reefs and Barrier Reefs, except that the former skirt the shore more closely, while the latter may lie at a distance of many miles from island or mainland.

It is impossible for the polyps to raise their stony structure above the sea. Some kinds can endure exposure to the air for a short time without dying, but only for a short time. A coral island, when first built, is merely level with the ocean-surface at low tide.

But old Ocean carries on the work which the polyps have begun. Heavy rollers break incessantly against the reef, loosening blocks of coral, some of which are flung bodily upon it, while others are pounded into sand, which fills up holes and crevices. Gradually thus the whole becomes cemented into hard reef-rock.

As this goes on the low island slowly rises, until it has climbed above high-tide level.

Then the task can only be completed by waves of exceptional reach. Still the grinding of coral to fine sand goes on; and in time it gains a depth of some inches. And the waves carry seeds and cocoa-nuts to the spot; and shrubs and trees spring up, to sow again their own seeds, and by gradual decay to form mould. Thus it comes about that a little island is made ready for man to live on.

One might expect these stages to be very slow indeed, but such events march at the double in tropical climates. In the Low Archipelago one atoll was found, in the space of only thirty-four years, to have been transformed from a mere rock-reef to a lagoon island, fourteen miles in length, with tall trees growing along almost the whole of one side.

As a specimen of the sizes to which coral-buildings reach, the Maldive Archipelago may be named. It is a vast collection of islands and reefs, stretching to a length of four hundred and seventy miles, and in parts fifty miles broad. Barrier-reefs, reaching through many hundreds of miles, are even more remarkable.

Travellers write stirring descriptions of the beauty of these erections. The vivid pen of Miss Gordon-Cumming, for instance, has painted many a picture of Pacific reefs, of thundering breakers, and dazzling white surf.

We are told by her of “the patches of coral, sea-weed, and sometimes white sand, lying at irregular depths beneath a shallow covering of the most crystalline emerald-green water,” producing “every shade of aqua-marine, mauve, sienna, and orange, all marvellously blended.” And, again, of the wonderful masses of living coral which grow like garden-plants below the clear water, and of branching shrubs of all imaginable tints, such as pink, blue, mauve, and primrose.

To pluck and carry off these ocean-blossoms would be a vain attempt, for the “gelatinous slime” to which the colours belong “drips away, as the living creatures melt and die, when exposed to the upper air.”

From the pen of another eye-witness[3] we have a description of a visit at low-tide to the barrier-reef of Levuka, the old Fiji capital. We learn that the reef itself consists mainly of dead coral—“rough, uninteresting, shapeless limestones, with a very small covering of seaweed.” But after about a quarter of a mile of difficult walking, the travellers drew near to the “roaring surf on the outside,” where “fingery lumps of beautiful live coral began to appear, of the palest lavender-blue colour.” By the time that they were nearly within touch of the spray, “the whole floor was one mass of living branches of coral.”

It was not, however, until they ventured actually into the water, beyond the outer verge of the “great sea-wall,” that they could see for themselves the true nature of the reef.

This was the description given. “You look down, and see a steep irregular wall, extending deeper into the ocean than the eye can follow, and broken into lovely grottoes and holes and canals, through which small resplendent fishes of the brightest blue or gold flit fitfully between the lumps of coral. The sides of the natural grottoes are entirely covered with endless forms of tender-coloured coral, but all beautiful, and all more or less of the fingery or branching species, known as madrepores. It is really impossible to draw or describe the sight.”

Equally impossible was it to photograph these fairy grottoes, “seen through twenty feet of surging water,” though some snapshots were taken in moments when the vast billows withdrew themselves.

One difficult question in connection with coral reefs has been—How can they rise, as they do, out of considerable depths, when coral-polyps cannot live below some twenty fathoms from the surface?

Two chief explanations have been offered, each of which has been warmly taken up and defended.

One meets the difficulty by means of the theory of a rising and sinking earth-crust. A mountain-top might have been first heaved up to within twenty fathoms of the surface. Then later, while the polyps were building upon it, the mountain might have slowly sunk. In that case the polyps below would die, as the water deepened; but the wall of dead coral would remain, reaching in time very far down.

The other explanation also admits that coral-reefs have been generally built upon sub-ocean heights. But it supposes that height to have been partly raised by volcanic forces, and afterwards built up to the needed height by a growing collection of oozes and animal-remains, deposited through ages.

Many proofs have been found in recent years of the probable truth of the latter theory. Still, it does not of necessity do away with the earlier explanation. Here, once more, the question may be asked—Why should not both be true? If some submarine peaks have been lifted to just the right level by gradual building up of sediment, others may have been so raised by volcanic action or crust-crinkling.

Either way, it is a marvellous tale.

Thousands of miles of solid reef-rocks; hundreds of substantial inhabited islands, all reared, inch after inch, by a mere “gelatinous slime,” by soft-bodied jelly-like creatures, first cousins to the dull though pretty anemone of our shores!

The thing sounds incredible! A stranger from some far-off world—a stranger even from polar regions on our Earth, unlearned in the lore of warmer oceans—might scout the story as absurd.

Yet no fact in Natural History is better attested, or stands on a firmer foundation. There is a good deal more in the philosophy of this small world than appears at first sight.