Popular Science Monthly/Volume 32/January 1888/Glimpses of Life Along a Coral Reef
|GLIMPSES OF LIFE ALONG A CORAL REEF.|
LAST summer (1886) I spent the month of June, with a party of naturalists from Johns Hopkins University, on Green Turtle Key, a small coral island near Abaco, Bahama, where we were engaged in the study of marine invertebrate life. In order to learn more of the general flora and fauna of the reef, I visited many of its rocks and keys which stretch in a long, broken chain northeastward of Abaco and the submerged banks connected with it. My friend who accompanied me was especially interested in birds, and was anxious to obtain specimens of the eggs and skins of the sea-fowl which breed in great numbers on these remote islands.
Abaco Island is roughly crescent-shaped (as shown by the accompanying map), its two horns pointing about northwest and south. With Little Abaco, which properly belongs to it, it is nearly one hundred miles long, and has an average width of twelve miles. There are six hundred and eighty square miles in the larger island alone. The greater part of its outer side, facing the ocean, is bordered by an inner reef of small keys and rocks, which trend northwest by southeast,
and form a channel about five miles wide, having a depth of from one to two and a half fathoms. Two or three miles farther out there is a second reef, mostly submerged, beyond which the bottom falls abruptly to the abyssal sea. The larger islands extend through one degree of latitude, from nearly 25° 50' to 26° 50'.
We left Green Turtle on the 15th of June in a sail-boat, with two men to pilot and assist us. Our older guide, Curry, was a native of the island, and made his living by fishing and sponging. His services were invaluable, as he was not only invariably obliging, but knew every rock and key in the reef, and could readily tell them at a long distance by their slight differences in contour. The position of our key, which we had left behind, was shown by the top of its tall cocoanut palms long after the island itself had dipped below the water. Taking a northwest course up the channel, Abaco is seen as a low barrier on our left, while at a greater distance it looks like an undulating green ribbon between the sky and sea. We pass numerous small keys
and rocks on the right, between which long white lines of breakers may be seen, marking the outer reef. We are frequently near enough to the "mainland" to see its dense forests of pine, its palms fringing the shore, the narrow beaches of white coral-sand, with here and there a thatched hut fronting a pineapple field, which may be distinguished by the small clearings in the woods.
The keys present the greatest variety in size and form, from a bare rock no larger than a buoy to islands five or six miles long. The latter are very narrow, and are usually covered with a thick growth of shrubs and small trees which, excepting a few palms, rarely exceed fifteen or twenty feet in height. The islands are scattered along closely together, or occasionally separated by wide channels. The soil has to be very thin indeed, which can not support a variety of shrubs, which seem to grow out of the very rocks and to live upon the air. Some of the smaller keys are mantled with vines and climbing plants, such as smilax, convolvuli, and rock samphire, with here and there some low shrubbery at the water's edge.
The coral-rock which forms the basis of the islands crops out at many points, and is always exposed around the shores where these are not covered by a sand-beach. Freshly-broken surfaces have a light-cream color, but weather to a uniform grayish tint. This limestone is so soft that it can be readily sawn or chopped with an axe. Consequently, the waves denude it rapidly, forming the white coral-sand, which is distributed as a fine deposit over the sea-bottom and as stretches of smooth beach. The shores overarch where they are at all precipitous, roofing a wide cavern below, in which the ceaseless roar of the waves may be heard at a long distance. Where a single rock stands alone, it is usually so much undermined that it resembles a low table with a single huge leg. There is a large perforation through the rocks at the southern extremity of Abaco, known as the "glass window," and also several submarine passages extending from one side of the island to the other. The rain carves grotesque forms out of the soft stone. This is sometimes coarsely honeycombed, or bristles all over with pinnacles or miniature chimneys, which are sharp as knife-edges, and compel you to use much caution in walking.
Fig. 3.—Two characteristic Coral Keys as seen from off the Northeast Coast of Abaco. (The tallest trees are Cocoanut Palms. The eroded table-shaped rock between the islands is from a sketch made at another point.
The dark-green foliage of the keys is frequently bordered by white, glistening lines, indicating beaches of coral-sand, which reflect the sun's rays with great power. Cocoanut palms find foothold along the shores, growing spontaneously from nuts cast up by the waves. In going northward from Green Turtle we pass successively Crab, Fiddle, Mun Jack, Ambergris, Spanish, Pensacola, Umbrella, Fish, Carter, Joe Keys, etc., and, in an opposite direction. Pelican Key, No Name Key, Great Guana Key, and numerous others.
The sharp contrast between the ordinary "white water" of the bay and the deep blue of the sea beyond the reefs, is very striking. The irregular black patches seen everywhere in the channel are due to algae or similar plants growing on the bottom. The sea-floor between Abaco and the reefs is elsewhere covered with the white coral-sand which causes a marvelously brilliant color-effect in strong lights, the tints ranging from the richest emerald to a transparent greenish-white.
Numerous sea-fowl show themselves as we sail past their haunts: brown pelican, standing immovable like statues on the rocks, but suddenly expanding into birds of astonishing size; men-of-war or frigate birds, whose dark, cleanly-cut forms are strongly silhouetted against the sky; flocks of black-headed gulls, standing in military order, each facing the same way, on the rocks, rise and whirl off at our approach.
At Fish Key we found a large colony of the sooty terns (Sterna fuliginosa), or "egg-bird," as the natives call them, just beginning to breed. This is a collection of wild-looking rocks, rising ten or fifteen feet above the sea like a row of petrified sand-dunes, which in reality they probably are, and covered with low shrubbery, grasses, and vines. When a long way off we noticed the birds hovering over the place, and on landing, their numbers increased until the air far above and around us fairly swarmed with the gliding forms of this graceful tern, and the strange medley of their harsh cries, together with the whirring of thousands of wings, was nearly deafening. They were nesting amid a tangle of shrubs three or four feet high, along a low, narrow ridge of one of the islands, a few yards from the water. Parting the bushes aside, we could see the old birds sitting on their eggs, and caught with our hands several which were snared in the vines as they attempted to fly. This tern resembles a large and powerful swallow. It has a sharply-forked tail, snow-white neck and breast, while the rest of the plumage is a dead black. They nest close together under the bushes, laying a single egg on the ground, without nest of any kind. Their eggs are easily distinguished from any others which we saw, being white or creamy and boldly spotted all over with umber and lilac. Even in these remote places the numbers of sea-birds are being yearly lessened by the natives, who persistently collect their eggs for food. The rare flamingo is now reduced to a colony of a few hundred on Abaco, where, as I was informed by an old settler, they numbered thousands several years ago, and similarly the beautiful tropic bird, which is hunted chiefly for food, is being gradually exterminated.
Close beside this key there was a small rock a few yards square, with scarcely a spear of grass upon it, which a party of the Wilson's tern (Sterna hirundo) held in undisputed possession. Their cone tipped, olive-green, and spotted eggs lay in twos and threes on the bare surface of the limestone. Both this bird and the smaller edition of it, the least tern (S. superciliaris), which has similar habits, are called "shanks" by the islanders, while on the North Carolina coast (where we found both species breeding a month before) they are known to the fishermen as "great" and "little strikers." The Wilson's tern has a wide range, and is one of the most beautiful of a large and exceptionally striking family. It has a prominent black crest and coral-red bill and feet. Like many of our most attractive birds, it is shot down each season tothe widespread demands of a barbarous fashion. Its pearly wings, or as often the whole bird, usually much distorted by the milliner, may be seen almost any day in the streets, pinned on to ladies' hats.
As we approached Paw-paw Key some tall bushes on the island appeared to be draped in deep mourning. Presently, as a large black company of birds rose one after another in the air, we recognized the frigate-bird (Tachypetes aquilus). I counted seventy of them as they soared above our heads. These swarthy giants cut a memorable figure against the sky, with their great angular wings, and long, forked tail. They mount slowly upward in spiral curves, with all the ease and grace of the hawk, until a safe height is reached, when they sail rapidly off to a distant island. The females are recognized by a conspicuous white spot on the breast. We witnessed the ascension and retreat of this pack from the same key on our return a few days later.
This little island is nearly bare except for the carpet of vines and low bushes. A few specimens of the Conocarpus called here "button-tree," are growing along the water's edge. It is ten or fifteen feet high, and may be easily told at a glance by its silvery foliage. Its flowers are inconspicuous, in small globular heads, but they are quite fragrant. This and the Rhacichallis rupestris, called "seaweed" by our boatmen, are characteristic of all these islands. The latter is semi-prostrate, and has fine, spray-like foliage, resembling an evergreen. Its light-gray bark is noticeable and also its small saffron flowers. This shrub is very common on the exposed rocks just above high-tide mark, where various mollusks are found in great numbers. One univalve (Tectarius), nearly an inch long, is especially abundant. The rocks are peppered with them, and clumps of several hundred together are sometimes seen. It climbs up the stems of the Rhacichallis, on which it probably feeds, and seems to derive a double protection, from the colors of both the coral-rock and bark of this shrub, which it perfectly simulates.
Before landing at this key we had seen a large, black bird emerge from a mass of twigs in a bush overhanging the water, and, with its long neck outstretched, fly to an adjacent part of the island. This proved to be the Florida cormorant (Phalacrocorax) and its nest. I soon saw a number of these birds standing in line on a sand-spit with heads erect, like a squad of soldiers at drill. The nest was a shallow, rudely-built platform of twigs and grass, and contained three long,
bluish-white eggs, of a coarse, chalky texture. We found several nests on the island, most of which had been just completed. The long neck and thick stub of a body gives the cormorant a comical appearance, whether it is on the wing or walking erect on the beach. This species has sooty-black plumage, a yellow throat, and a blue rim round the eye. The bill is long and cylindrical, the upper mandibles curving over the lower in the form of a sharp hook, and the lining. of the mouth and gular-pouch is bright blue. The long, black quills of the frigate-bird were scattered over the island, and the bushes were whitened with their ordure.
I had not been many minutes on the key before I discovered a large snow-white bird nestling on the ground under a spray of Rhacichallis. Its wings were barred with jet-black; its bill was bright yellow, and tapered to a spear-like point, which forbade too close familiarity. This proved to be the yellow-billed tropic-bird (Phaeton flavirostris), and we afterward caught several in our hands, taking them from the nest. When held up by the wings, they strike lustily with their bills and utter a peculiarly shrill cry. The tropic-bird lays a single egg on the ground beneath rocks or bushes. It is about the size and make of the hen's, and is finely sprinkled with reddish-brown so as to appear of an almost uniform tint. One of these birds which my companion shot and slightly wounded, flew a short distance and then alighted on the water. As we sailed toward it, first one and then another bird came and hovered over it as if urging it to take flight, which It presently did, and with its attendants soon passed out of sight. These birds resemble the gulls in many points, but are distinguished from other sea-fowl by two long streamers in the tail, which wave behind them as they fly.
Joe Key, forty miles northwest of Green Turtle, was the most interesting island we visited. Its windward side, facing the sea, is rocky and precipitous A mangrove-swamp nearly divides it into two, and on the inside there is a smooth beach and a good harbor for small boats. It was nearly dark when we landed, but our attention was soon called to the great numbers of pigeons which were constantly flying to and fro from one point to another on the island. Before going ashore, we rowed to a narrow inlet between a detached cliff and the main island, through which the tide flowed with a rapid current. Fish may be always found at such places, where they are apparently on the lookout for the food swept back and forth by the tides. Here our guides captured two fish in as many minutes, which were more than enough for our breakfast and supper. The largest of these was the grouper (Epinephelus morio) a thick, powerful fish of a dull, reddish-olive color, with a square tail like a cod. The other, the barracouta or sennet (Sphyræna picuda) has the shape of a pike. Its jaws are armed with long, projecting teeth, Neither of these fish are especially esteemed, but of the two the barracouta is the best. The inhabitants of these islands capture most of their fish and the turtle with the "grains" or spear. A water-glass also is usually carried in the boat. The grains is an awkward weapon, but in skillful hands a most effectual one, consisting simply of a spear-head attached to a rope, at the end of a long pole.
Above the sand-beach there were two small springs, where our guides scooped up enough water to fill a small keg. These were merely holes dug in the sand scarcely above high tide, and contained decidedly brackish rain-water, which, however, could be rendered palatable by boiling and by the addition of lime-juice. The swamp was bordered by an almost impenetrable growth of shrubbery and small trees, in which were hundreds of old pigeons' nests. The ground was literally strewed, particularly under the trees, with an interesting species of hermit-crab, which inhabits the empty shells of a common whelk. These crabs are of a chocolate-brown color, and have one large swollen claw. They areactive, climbing steep surfaces with ease, and probably ascend trees.
We could hear the whirring of hundreds of pigeons overhead, and their peculiar cooing, cu-oo-cu-oo-cu-hu-hu, which has a singularly melancholy sound in the woods at dusk. It is impossible to see out of these tangles where the branches and vines interlace over your head, and it is sometimes necessary to climb up and take your bearings. At the hour of twilight the pigeons are approached without difficulty. Besides the white-crowned pigeon (Columba leucocephala) there was also another species, called the "rock dove." The former is of a nearly uniform plumbeous blue, excepting its snowy crest. The rock-dove is more brilliantly marked with brown, and iridescent green and blue. It is a pretty sight to see hundreds of these birds sitting erect on the trees, and to watch their rapid, incessant flight. If one is disturbed, all within gunshot take wing, and circle rapidly over the trees, sometimes encompassing the island before settling again. These birds were apparently about to breed here very soon.
There was a palmetto-grove on this island, in which a recent fire had burned away all the undershrubbery, leaving a clean floor to walk upon, and the charred trunks and new foliage of some of the palms showed how closely they also had escaped. These trees have great size of trunk compared with their height, which gives them a decidedly dwarfed appearance. Some swollen boles, a foot or so in diameter, are only four or five feet tall. A pendulous spray of fine creamy flowers hangs down from the base of the leaves. This is succeeded by a small nut or berry, dried specimens of which were still on the trees. Many of the trunks were tattooed by a woodpecker, which also breeds on the island, as shown by its old nesting-holes.
The mosquito, which abounds everywhere along the keys, did not trouble us here, but the pest of the place was a microscopic midge, called the "sand-fly," with black bead and transparent body, whose burning touch was like that of a sharp needle on the skin.
The Bahaman red-winged starling, looking much like our northern species (Agelaeus phœniceus), of which it is a variation, was common, and probably breeding on this key. It delivered its flute-likeas assiduously from the top of a palm as its relative does his from the button-bush or alder of a New England meadow.
The black-headed or laughing gull (Larus atricilla) was nesting here also, as well as at most points where we touched. It is a common resident all along the South Atlantic sea-board. We found its nests and eggs at Portsmouth, on the North Carolina coast, the last week in May. It is easily distinguished by its black hood, which completely covers the head, ending abruptly on the neck. This cap is, however, exchanged for a white one in winter. These birds dwell in small colonies on the rocky keys, nesting a few feet above high-water mark. The nest is indifferently made of grass and seaweed, varying much in the amount of materials used, and contains from two to three large, olive eggs, mottled or spotted with darker pigment.
A handsome spike-grass (Uniola paniculata), whose wavy plumes are sometimes six feet tall, grows above the sandy beach. This same species occurs along the coast from Virginia to the Gulf of Mexico, where it is called "sea-oats." The green blades of the "West Indian lily" (Pancratium Carolinianum), a member of the Amaryllis family, are found growing in large clumps at the water's edge. Its flowers, which were now nearly past, are pure white, and remarkably fragrant. We found here also the Sabbatia gracilis in the sand, and a small leguminous tree, with clusters of reddish flowers, at which I saw the Bahaman honey-creeper—a delicate little warbler—busily at work.
The Cuban nighthawk (Chordeiles minor) was breeding here, as at several other islands which we examined. It is called "pilepedick," from its peculiar note, which is well reproduced in the name. It has many of the characteristics of the bull-bat of the Eastern United States, tumbling along the ground as if its wings and legs were broken, if surprised on its nest, and producing that peculiar booming sound when on the wing by sweeping down from a great height in the air. The young, which we found as frequently as the eggs, resemble a pinch of gray down, and so perfectly do both they and the eggs match the gray rock on which they are laid, it is only by a rare chance if you find a nest without flushing the old bird. The young nighthawk is about as broad as long, and, unlike the callow young of most birds, it is covered from head to foot with a thick coat of down.
On our return we anchored the first night in a little harbor at Allons' Key, where two small fishing-boats had already taken refuge from a threatening squall. We saw the ruins of several huts on this island, and the remains of a small grove of cocoanut trees, which had been blown down in the destructive hurricane of September, 1884, The place was so infested by mosquitoes that this little settlement had to be abandoned. It rained heavily in the night, but our men took an early start, and awoke us the next morning at five by announcing the discovery of a
"loggerhead's track." The beaches had been leveled by the rain, so that any new impression could be readily seen. The turtle had ascended the beach to a point above high tide, had stirred up the sand, leaving a great heap over her eggs, and returned to the water but a short time before we landed. This was shown by the ebbing tide, which had retreated only a short distance from her last tracks. The eggs were laid in a bunch, and covered with sand a foot and a half deep. There were just one hundred and thirty-nine of them. They resemble a white rubber ball, an inch and a half in diameter. The sea-turtle's eggs have a peculiar flavor, but are very palatable. The glair becomes tough and leathery by boiling, and is always thrown away. The breeding-season of the loggerhead (Chelonia caretta) lasts from May well into August, according to the statement of our guide, who also said that they deposited eggs several times in this period, producing as many as one hundred and eighty at the first laying, and perhaps no more than two or three at the last. The natives make a business-like search for these eggs each year, and sometimes surprise the female turtle on the beach. When she has once begun the egg-laying process, it has to be finished, even if she is turned on her back and made a prisoner immediately after. The extraordinary egg-producing power of these animals is all that preserves them from immediate extinction. 
Large forest-trees, such as pine, cedar, and mastic, which grow on Abaco, do not occur on the keys. We find here, however, smaller trees and shrubs in great variety. Besides those already mentioned, there are three palmettos, called the "silver" and "thatch-top palms," and "hog-cabbage"; "sea-grape" (Coccoloba uvifera); the "seven-year apple" (Genipa clusiifolia); Malvaviscus arboreus, a handsome shrub, with red flowers, resembling a small hollyhock; mangrove [Rhizophora mangle); wild sapodilla (Sapota achras); and many others equally characteristic. Land-snails are very common on some of the islands, and the omnipresent lizards (Annolis) were the only reptiles which we met with.
The Genipa or seven-year apple is very abundant along the shores of the islands just above high-tide mark. It sends up from the ground slender brittle stems a few feet high, bearing creamy-white flowers and a hard, yellowish-green fruit, which is inedible. The leaves are dark green and highly polished.
The wild sapodilla is equally common, and attains the height of a small tree. The axillary flower-clusters appear a little in advance of the leaves, which in June add a touch of the brightest spring green to every thicket. The fruit, which is not edible, is covered with a rusty-brown skin, and is usually terminated by the long persistent style. The cultivated sapodilla forms a good-sized tree, and appears to grow spontaneously wherever it has been introduced. It differs from the former chiefly in point of size and in the superiority of its fruit. Possibly the wild form is the parent stock from which the other, with its sweet, pulpy fruit, has been derived; but I have been unable to gather any facts relating to this point. A milky juice flows freely from the wounded bark of the sapodilla-trees, forming a viscid gum, which the negroes use as bird-lime. It is also noteworthy that the Isonandra gutta, a. Malayan tree, from the juice of which the gutta-percha of commerce is obtained, is also a member of the Sapotaceæ or Sapodilla family.
These islands have been largely colonized from the South, principally perhaps from Cuba; and the Gulf Stream and other agents, which have brought the plant-germs thither, have carried them also to the keys and coast of Florida, where they may have first become established. The seed-eating birds, finches and starlings, which are common on Abaco and many of the small islands, serve also as important distributors of grains and seeds of other plants. The great number of shrubs bearing edible berries may be partially accounted for in this way. The annual hurricanes, on the other hand, are certainly powerful agencies in scattering seeds over wide areas. Knowing the frequency of their occurrence and their long duration, we can see how by this means alone an island would soon acquire a rich and varied flora.
- Some time ago a large grouper was speared by a fisherman off Sand Key near Nassau, and twenty-two young loggerheads were found in its stomach. This fish was doubtless feeding along the shore, and had evidently snapped up the young turtles just as they were making their début in the water. Thus it seems that these animals have to contend with enemies which are even more formidable than man, and it not surprising that this valuable and once staple product of these islands is fast becoming a luxury.