Popular Science Monthly/Volume 76/April 1910/The Research Work of the Tortugas Laboratory
|THE RESEARCH WORK OF THE TORTUGAS LABORATORY|
MARINE BIOLOGICAL STATION OF THE CARNEGIE INSTITUTION AT TORTUGAS, FLORIDA
NEARLY seventy miles west of Key West, out in the Gulf of Mexico and in the most isolated situation occupied by any islands off our coast, lie the seven small keys of the Tortugas. Between them and the Cuban coast flows the great current of the Gulf Stream, and to the eastward of them lie forty miles of open water beyond which are their nearest neighbors, the Marquesas Keys of Florida. The Tortugas are the most westerly and southerly and the newest geologically of all those coral and limestone islets which are strung chain-like one after another in a long graceful sweeping curve from Cape Florida southward and always westward to end in the Tortugas.
The Tortugas Keys are low, being only as high as the winds and waves can toss the shifting sea-sands which compose them, for they consist entirely of wave-broken fragments of shells with here and there the stony skeleton of a seaweed, echinoderm or dead coral. Every particle composing them was once part of a living creature in the ocean which surrounds them, and thus the islands are but the dead remains of living things that were. A stunted twisted growth of bay cedars and cactus clings to their sandy soil and defies the salt spray which in time of storm drives completely over the islands. Almost every plant surviving upon the Tortugas is tough-leaved and juicy inwardly, or it sends roots far down through the sand to the salt water, for the rain serves but poorly to moisten the loose sandy soil through which it filters rapidly. The Tortugas Keys constitute the rim of an irregular atoll enclosing a lagoon with many a coral patch rising ominously out of deep blue water to within a few feet of the surface. In the old days tradition says that its harbor was the retreat of many a pirate safely anchored in the midst of the maze of its coral reefs.Yet the islands, although remote, are not desolate to the naturalist, for all around them lies the deep blue of the tropical ocean, its ripples flashing merrily in the brilliant sun, and looking downward through the crystal depths one floats above the richest coral reefs of the Florida region. No butterflies of an East Indian jungle outrival the brilliant fish which glide languidly in and out among the purple sea-fans bending majestically to the surging sea. Hundreds of creatures find their homes among the caverns of the coral reef, or under the great carpets of rich yellow and olive sea-anemones which overgrow the naked rock
that once was living coral; and the Gulf Stream, that greatest carrier of floating life, flows close to the Tortugas, and the southerly and easterly winds of the summer months constantly drive its dark blue waters upon the islands.
It is on account of these things that the Carnegie Institution of Washington, seeking always to promote research in fields that others can not, or dare not, venture to explore, has established a marine laboratory upon Loggerhead Key, Tortugas. The station is still young, its first season being that of 1905.
The era of finding and naming of animals which had its dawn with Linnæus and its noonday of splendor with the great French naturalists has waned into its dignified decline. Not that systematic zoology will not accomplish much in the future, but the days of its great achievement are in the past.
Therein, indeed, lies the opportunity of the Tortugas laboratory, for a new science has arisen phoenix-like above the ashes of the old. Modern biology is now but little concerned with the naming of dead things, but the study of the living has become of paramount importance. All problems necessitating the study of living animals have been neglected in the tropics, yet there in the pure water of the Gulf Stream one may conduct such experiments with extraordinary success. It is through the study of living animals that science has already discovered truths of incalculable benefit—the control of malaria, yellow fever, and the hook-worm—but a mere beginning has been made in this new science, and, if unrestricted by ill-considered legislation, its future promises far more than its brief past has given us.
As Franklin said when asked the purport of the study of so trivial a set of phenomena as those of frictional electricity—"Of what use is a baby? It may become a man." Who could predict that a reflection of the sun from the windows of the Luxembourg would reveal to Malus the secret of polarized light, and lead ultimately to the most accurate analysis of sugars. It is a reflection upon our lack of confidence that in this age one must still plead for the cause of pure science, for everywhere about us we find practical applications rendered possible only through the previous discovery of their underlying principles by students whose inducement to labor was their love of science, not the hope of financial gain. Thus it was that Henry paved the way for Morse's telegraph, Faraday's classic studies rendered possible the dynamo and electric motor, and the researches of Hertz found their practical application in the development of wireless telegraphy.
Fifty years ago Darwin changed biology into a philosophical science, but it is only recently that it has exhibited decisive evidence of passing out of the qualitative into the quantitative stage of its development.Thus it is that in these days a marine laboratory is dependent not
mainly upon a rich and varied fauna, but upon the presence of animals which may be found in abundance in its immediate neighborhood, and which provide favorable subjects for experimental studies.
When we contemplate the vast numbers of so-called researches published every year, it becomes evident that science will be advanced more surely by improving the quality of these papers than by increasing their bulk. For a generation the civilized nations of the world have at great expense maintained experiment stations to improve the breed of plants and animals useful to man, but nearly all of them have labored under the false impression that researches can be produced at stated intervals. Much of that freedom so essential for research was sacrificed to the production of bulky annual reports restricted to the accounts of "purely practical" studies. It was not an accident that Mendel, laboring obscurely in his cloister garden and with no thought save but for nature and her ways, discovered the law of heredity which all the experiment stations in the world failed to find.
Anton Dohrn did well for science when he gave his fortune to build the Naples Laboratory, but he did far better when he granted to those who labored there unlimited time and boundless freedom in thought and action, and his confidence was rewarded, for at Naples have been produced many of the greatest papers known to biological science.
Concentrating its efforts solely upon research, the Tortugas is in no sense the rival of other educational institutions, its simple object being to supplement and extend the work which others are attempting, or to render possible the prosecution of researches which no other institutions can undertake. Indeed, the success of any research laboratory must depend upon the efficiency of the training which its investigators have received at institutions of both instruction and research, such as the laboratories at Woods Hole, Cold Spring Harbor, Bermuda, South Harpswell and St. Andrews.
At Tortugas some of the ablest investigators of our country have been directing their attention not only to the systematic study of the rich reef fauna of the region, but mainly to problems in physiology, ecology, regeneration and embryology. We shall have space for a review of the results of a few only of these studies, selecting such as may be of the widest general interest.
Throughout the autumn and winter one of the most desolate of the Tortugas Islands is the small uninhabited Bird Key; but suddenly on a day late in April or early in May a cloud of sea-gulls gathers from far and near, and soon more than 25,000 birds are screaming over the island, struggling for nesting space.
Undeterred by the roasting heat of desert sands, the air above which rises to at least 120° F. on every sunny summer's day, or by the ceaseless shrieks of sea-gulls, Professor Watson, of Johns Hopkins University, lived nearly three months upon Bird Key. He reared the young birds and found that they could learn their way through a maze to their food. The adults could also learn to overcome obstacles in seeking to sit upon the eggs. The noddy gull builds its nest in bushes and while
so doing is quite shy, but if an egg be placed in the nest the mere sight of it causes the bird to lose all shyness, and it sits upon the egg as if it were its own. Both male and female cooperate to build the nest, but the male alone procures food for both during this period, the female constantly guarding the nest. After the egg is laid, both male and female fly away to fish and take their turns in brooding the egg at intervals of about two hours. The egg hatches after 32 to 35 days. But the noddy gull does not recognize its own egg, but will readily incubate the egg of the sooty tern or any object colored or uncolored bearing more or less resemblance to an egg. It recognizes the locality of its nest however, and returns to the old locality if the nest be moved, but it will accept an artificial nest placed in the old nest locality without hesitation. Dyeing one of the mates in strange colors causes the undyed bird to attack it, and indeed all other birds upon the island displayed excitement at the appearance of a dyed bird.
The sooty tern nests upon the ground, and recognizes the exact locality of its nest, if, however, the nest be raised vertically, the bird, but little disturbed, alights upon it, then if after an interval it be lowered, the bird attempts to alight in the air above the nest in the place where the nest was formerly. A slight horizontal movement of the nest causes great confusion in the bird.
Professor Watson caused adult birds to be taken from Bird Key to Havana, 92 miles; to Key West, 66 miles, and to Cape Hatteras 850 miles from Bird Key. Birds liberated at these places returned in a very short time to their nests on Bird Key. The sooty terns returned from Cape Hatteras in five days, and as they probably flew along shore and not by the straight-line route, they must have flown at least 1,081 miles. This is a most striking experiment, for Cape Hatteras is far to the northward of the northern limit of the geographical range of these birds.
Another Tortugas research was that of Professor Reighard, of the University of Michigan, who worked upon the subject of warning coloration.
For a long time Darwin was puzzled by the fact that many animals are conspicuously colored and yet their habits are such that they openly display themselves to the view of all possible enemies. Why, then, were they not exterminated? That brilliant yet modest man, Alfred Russel Wallace, came forward with an ingenious hypothesis, now well known as the theory of warning coloration. He assumed that such conspicuous
animals possessed poisonous or disagreeable qualities which rendered them unpalatable, so that their enemies soon learned to recognize them as uneatable, and thus the more conspicuous their appearance, the more surely were they protected.
It has been assumed that the beautifully colored fish which swim so unconcernedly and slowly in and out among the caverns of the coral reefs were good examples of warning coloration, for over the sandy
bottom around the corals swims the gray snapper, the commonest predaceous fish of the reefs. Yet these gray snappers are not seen to attempt to devour the reef fishes. Professor Reighard found, however, that when lie captured these beautiful reef fish and threw them in among the gray snappers far from the reefs they were greedily devoured without a moment's hesitation. It became evident that the gray snapper could not capture the brilliant little fishes as long as they enjoyed the protection afforded by the stings of the coral polyps, or remained near the entrances to the intricate caverns of the reefs. Hence these fishes are not warningly colored, and Wallace's hypothesis does not apply to them.
Nevertheless, Professor Reighard found that the gray snapper could distinguish colors, and that it could be taught to associate a brilliant coior with an unpleasant taste.
In order to prove this, he made use of the little silvery sardine (Atherina) which swarms in thousands over the shallows of the reefs, and whose only office in life seems to be to supply food for all larger fishes. Reighard dyed these silvery fish a brilliant carmine red and the gray snappers devoured them without hesitation. Then, however, the tentacles of a medusa were placed in the mouths of the red-colored sardines and the gray snappers soon learned after a brief experience with the stings to avoid them; and they remembered to avoid red-colored sardines after an interval of twenty days had elapsed since they had last seen them, although these later red fish had no medusa tentacles in their mouths. Thus he created a warning coloration; something nature herself had not done.
Professor Reighard's experiments are by far the most convincing that have ever been carried out upon the subject of warning coloration, being performed in surroundings natural to the animals themselves. He concludes that the conspicuous coloration of coral-reef fishes is is not for warning enemies, and is the result of race tendency unchecked by selection.
Another research of interest was that of Dr. Stockard, of the Cornell Medical College, upon the habits of the walking-stick insect, Aplopus, which lives upon the bay cedar (Suriana) bushes at Tortugas and bears an extraordinary resemblance to a stick of the bush itself, while its eggs resemble the seeds of the same bush. Professor Stockard finds that the habits of the insect accord perfectly with and enhance the value of its protective coloration. The insect is active only at night, or in darkness, and in daylight they may be piled one on top of another, remaining motionless as real sticks in any attitude, but if they then be placed in the dark they immediately scramble off in all directions.
In another research Dr. Stockard studied the regeneration of the claws of the snapping-shrimp Alpheus which lives within the cavities of sponges. This little lobster-like animal has one very large claw and one small one, and when captured it snaps the nippers of the large claw, producing a sound resembling the sudden cracking of thick glass, so that one imagines that the aquarium has broken. It is well known
Fig. 9. Cassiopea xamachana, the Jellyfish of the Moat of Fort Jefferson. Tortugas.
from the work of Prizbram that if the large claw of Alpheus be cut off the small claw changes to a large one at the next molt.
Dr. Stockard finds, however, that if the large claw be removed and at the same time all legs of the opposite side of the body except the small claw be cut off, the small claw does not change into a large one and the animal acquires two equally developed small claws at the next molt. Thus a tendency toward a reversal is checked.
In another research, Dr. Stockard made the interesting observation that when a piece of a jellyfish (Cassiopea) is cut away and the animal starved a new piece regenerates, even though the old part of the body shrinks in size to provide it nutriment. Cancers also grow in this manner at the expense of the surrounding tissues, and thus there appears to be an analogy between the mode of growth of cancer and regeneration. Possibly, then, if we could control regeneration some similar process might be found effective to check the growth of cancer.
As is now well known to naturalists, Tower has succeeded through the influence of heat and moisture in producing a new sort of beetle which breeds true as would a newly arisen species. MacDougal has also succeeded through chemical means in effecting the same result with plants. Recently, at Tortugas, Professor Tennent, of Bryn Mawr, produced hybrids by reciprocal crosses between Hipponoë and Toxopneustes, two common sea-urchins of the reefs; and he discovered the interesting fact that if the sea-water be normal or rendered alkaline the larvae resemble the Hipponæ parent, but if the sea-water be treated with an acid so as to reduce its alkalinity the larva? resembled their Toxopneustes parent. .He could then by changing the external conditions produce larva? resembling either parent he choose, and thus alter the dominance of either parent at will.
No one knew what caused the newly hatched young of the great sea-turtles to crawl toward the ocean as soon as they had dug their way upward out of the sand within which their eggs are laid, but Dr. Davenport Hooker, of Yale, found that the young turtle is attracted toward the ocean by the blue color of the water. If it sees the ocean through red, yellow or green glass it does not crawl toward it, but if a piece of blue glass, or even blue paper, be placed anywhere within range of its vision the turtle at once scuttles toward it with great excitement.If one goes out upon the ocean before sunrise on the morning of a day within three days of the time of the last quarter of the July moon, the surface will be found to be covered with actively wriggling worms, about six inches long, swimming in all directions. These are the posterior ends of the Atlantic palolo worm (Eunice fucata) which breaks off from the head end of the animal and swims upward from the crevices of the coral reef, to take part in the breeding swarm. Professor Aaron L. Treadwell, of Vassar College, is now studying this phenomenon, and he has discovered that if the rocks containing the worms be placed in a dark chamber upon the day preceding the night of the swarm the worms may still swarm. Hence, contrary to Mayer's supposition, the presence of moonlight is not necessary for the swarming reaction. Previous studies at Tortugas have shown that the
Dr. T. Wayland Vaughan, of Washington, finds that the line of the Florida Keys from Soldier's Key to the southeastern corner of Big Pine Key is composed of elevated coral-reef rock. The northern end of Soldier's Key and all keys to the northward of it are composed of quartz-bearing sands mingled with broken shells. The keys from Key West to Big Pine Key, with the exception of the southeastern corner of the latter, are composed of limestone mud which long ago was elevated above the sea and changed into rock, so that now one sees a net-work of old mud-cracks in the rocky floor of the pine forest. On the continental side of the line of coral-reef keys and extending transversely to them are long shoals formed by the settling of lime mud in the slack water between the currents which flow in and out with the tides through openings between keys. These shoals become covered with mangroves, and thus finally elevated above the surface of the sea. There are many other interesting geological observations made by Dr. Vaughan which limitations of space prevent us from reviewing.
In addition to his studies of the geology of the reef's, he is making
the most accurate and extensive investigation of the associations, habits, rate of growth and constitution of corals ever attempted by any naturalist. He is rearing corals from the free-swimming larva, and observing their rate of growth as well as studying the growth-rate of many coral beads found living upon the reefs or in the moat of Fort Jefferson. Years must elapse before the results of these studies will be ready for publication, but he has already discovered that under favorable conditions the rate of growth of corals is surprisingly rapid, and that the free-swimming stage of the planula lasts long enough for corals to be drifted fully 800 miles by the Gulf Stream.
Professor Edwin G. Conklin, of Princeton, finds that the egg of the scyphomedusa Linerges consists of an outer layer of clear protoplasm, an intermediate shell of densely packed yolk spherules and a central sphere of dissolved yolk. The outer layer of the egg forms the peripheral layer of the gastrula and blastula, and gives rise to the cilia of the ectoderm. The middle layer constitutes the principal part of all of the cells of the body, while the central yolk serves for nourishment. Thus animals so low as the jellyfishes show the beginning of that differentiation of organ-forming substances in tne egg which Professor Conklin discovered was so characteristic of the eggs of higher forms. He also finds that the gastrula larva in this medusa may be formed either by invagination or by unipolar ingression, thus showing the intimate relationship between these apparently distinct processes.
Dr. E. P. Cowles, of Johns Hopkins, carried out an extensive series of observations upon the habits and reactions of the ghost crab Ocypoda arcnaria, which lives upon the sandy beaches of the Tortugas. It will be impossible to do more than present a few of his most important results. He finds that this crab can not detect color, but is sensitive to large differences in the intensity of light, and it readily perceives a moving object. The color pattern of the crab changes under different conditions of light and temperature, becoming dark and mottled in dull light and low temperature. It can not detect sound waves traveling through air, but its so-called "auditory organs" are actually organs of equilibration. The crab has memory, is able to profit by experience and can form habits.
Dr. Prank M. Chapman, of the American Museum of Natural History, discovered that the booby, Sula fiba, which nests upon Cay Verde, Bahamas, between February and April, lays two eggs but rears only one young bird. His observations and collections upon Cay Verde has led to the construction of a very attractive group in the American Museum of Natural History in New York illustrating the nesting habits of the frigate-bird and the booby.Pleasurable as the task would be, limitations of space prohibit my reviewing the results of the studies of Messrs. Brooks, Hartmeyer,
Harvey. Jordan, Kellner, Linton, McClendon, Osburn, Perkins and Pratt, all of whom have produced careful and important work.
The laboratory is very young; it can not yet claim to have been a success, for despite the fact that some of our ablest workers have seen fit to strive in its interests, the time which has elapsed since its foundation is too short to enable us to do more than to assert that with such generous self-sacrificing devotion to its cause as has been shown by those who have honored it by their labors, success will come with the vears that lie before it.