Popular Science Monthly/Volume 85/September 1914/An Expedition to the Coral Reefs of Torres Straits
|AN EXPEDITION TO THE CORAL REEFS OF TORRES STRAITS|
EARLY in September, 1913, the expedition of the Department of Marine Biology of the Carnegie Institution of Washington arrived at Thursday Island in Torres Straits off the northern end of Cape York.
Thursday Island owing to the deep water in its vicinity has grown to be a busy port of call, although it is barely a mile in length and is so completely surrounded by the larger members of the archipelago that only the most detailed British Admiralty charts records its name, and even the painstaking Captain Cook who first sailed past it in the "Endeavour" in 1770, merely notes it as one of the Prince of Wales Islands.
Yet to our eyes it seemed an important place. Four of us—Clark, Harvey, Mayer and Tennent, together with Mr. John Mills, the able engineer of our naptha launch, had come nearly half the distance around the world from the eastern states of America, while Mr. Potts had left his cloistered quarters in Trinity Hall, Cambridge, and Mr. E. M. Grosse, the artist, had joined the expedition in Sydney.
Thursday Island was the intended objective of our journey for Saville-Kent in his beautifully illustrated book upon the Great Barrier Reef of Australia had especially designated it as being the site par excellence from which to study the coral reefs of Torres Straits.
Our surprise and disappointment was great therefore when we found the coral reefs to be overwhelmed with a layer of mud above which only the largest corals could raise their heads and thrive. The region seemed an ideal one only for masses of fleshy, dull olive-green alcyonaria (Sarcophyton) superficially resembling huge lichens several feet in diameter. The remarkably strong currents with their freight of silt and mud were fatal to luxuriant coral growth and the echinoderm life was hopelessly deficient, so that even the cheerful Clark, as enthusiastic a collector as ever lived, was in despair.
Fortunately, Mr. Charles Hedley, of Sydney, the distinguished student of coral reefs, had in a measure prepared us for disappointment and had kindly told us of the clear blue ocean water and rich coral reefs surrounding the Murray Islands 120 miles from Thursday Island, within 5 miles of the outer edge of the Great Barrier Reef and 75 miles south of the coast of New Guinea.
To the Murray Islands therefore we saw we must go with all speed, a feat, however, somewhat easier to plan that to accomplish, for in the intervening region were hundreds of uncharted coral reefs, and of all the fleet of schooners at anchor in Thursday Island harbor but one would venture to undertake the hazard of the voyage.
No sooner did the owner of this daring craft agree to take us, however, than he and his vessel disappeared in the night, leaving us stranded upon Thursday Island.
In response to kind letters of introduction from the British Ambassador Lord Bryce, the officers of the Australian government were most cordial in their efforts in our behalf, and never did we appreciate their generous aid more deeply than in the present emergency, for at the request of the Honorable W. M. Lee-Bryce, Esq., resident of Thursday Island, Messrs. Arthur and Hockings permitted the use of their power, schooner Kestrel to transport Messrs. Clark, Grosse, Harvey, Potts and Tennent to Darnley Island only 25 miles from the Murray Islands.
In the meantime, Mr. Mills and the director of the expedition set out to sea in a small launch to search for the truant schooner which we finally found snugly anchored in the lee of the peak of a beautiful palm-clad island within 25 miles of Endeavor Strait.
The "recapture" of the schooner was speedily effected and soon we were scudding over the waters toward the elusive Murray Islands. Our crew were black, very black, and each man's nose was pierced so as to confer as romanesque an outline as it is possible to attain with an originally negroid nasal organ. Moreover, the captain's ears were slashed and torn in a manner to delight the heart of a rat-catching terrier. His weather-beaten face bore many a scar, and one eye seemed to have seen better days, but more perfect discipline one never saw maintained upon a schooner than that enforced by our erstwhile head-hunting commander. They sprang to obey his almost whispered orders with an alacrity that would have done credit to the crew of a man-of-war.
Without chart or compass we sailed over a sea marked "dangerous" on the maps we might have had but chose to dispense with.Each day we threaded our way among the intricate passages between jagged coral reefs, keeping in the deep blue between the patches of emerald-green edged with foaming breakers; and always the steady southeast trade wind urged us onward. At night, we lay at anchor close
under the lee of reefs and the drowsy roar of the ocean lulled us into sleep.
At Darnley Island we found our associates most comfortably housed in the home of the magistrate, Mr. T. Arnold Williams, from which hospital roof, indeed, they were most unwilling to be "rescued."
But at last the peaks of the three extinct volcanoes which constitute the Murray Islands loomed through the tropic haze, and still struggling among the maze of reefs, we made for Maër Island, the largest of the group and anchored under the lee of the mountain wall by the side of its palm-edged beach.
As our naptha launch approached the shore, the sands became black with natives all gesticulating in much excitement, but we were most cordially and kindly received by the magistrate and school teacher, John Stewart Bruce, Esq., who for more than twenty years has lived alone among the natives laboring to fit them to meet the oncoming of civilization. Throughout our stay on Maër Island, the constant kindness and excellent advice of Mr. Bruce was indispensable to the success of our studies, and incidents exhibiting his rare personal charm and high character we shall always recall as the happiest of our memories.
Through the kind permission of the government, we were allowed to occupy the courthouse and the jail for laboratory quarters.
The courthouse was an airy, cheerful one-roomed concrete building which the natives under the leadership and instruction of Mr. Bruce had succeeded in erecting after four years of the most strenuous and concerted effort in the history of the island.
The jail, on the other hand, was a flimsy hut of pandanus thatch, but it served admirably as a storehouse for our apparatus and supplies.
As may be imagined, our visit put an end to the orderly administration of island justice. Deferred jail sentences were henceforth the only sort that could be enforced upon wife-beaters and other disturbers of the serenity of the island, but an even more dreadful punishment was quickly devised by the chief, or Mamoose, who condemned malefactors to work for us.
This punishment, however, soon lost its sting in proportion as the fame of the achievements of Jimmie, our cook, became spread abroad. Four cups of strong coffee, five fish balls, a large piece of turtle meat, four bananas and a yam constituted an average 5:30 a. m. "breakfast" for our native assistants, so it may be imagined that starvation was not the rule of our camp.
The impression should not arise, however, that our native servants were reprobates, for those whom we chose were good and faithful. Indeed, we employed the same men who had served Professor Haddon, whose accounts have made the anthropological and geological aspects of the islands so well known.
Fortunately one of our party could claim the honor of Professor Haddon's personal friendship, an "open sesame" to the Islander's highest consideration, but despite the initial respect thus inspired, the natives soon decided that we of the scientific staff were all hopeless but quite harmless lunatics who were being taken around the world under the guidance of our engineer, Mr. Mills. Indeed the wonderful behavior of the launch and the miraculous achievements of "Johnmills" who could "saw iron" were soon immortalized in song and will doubtless remain as a revered tradition of the island.Maër Island is an extinct volcano which in its active days burst through the old limestone floor of the wide Barrier Reef plateau which
as has been shown by Andrews, Griffith-Taylor and Hedley, was once above the sea but is now submerged to a depth of from 90 to 180 feet. Shattered fragments of the old limestone are found imbedded in the ash crater of the volcano.
On the western side of the island, the crater rim rises to a height of about 750 feet, the seaward slope being steep and evidently determined by the angle of repose of the ejected ash.
In later times, however, the volcano appears to have exploded and destroyed the northern part of the crater rim, out of the break in which there flowed a tongue-shaped mass of lava which now constitutes the northern half of the island. The last volcanic activity issued from a small ash-cone in the cup of the old crater, and then the island lapsed into its unbroken quietude.
A luxuriant growth of cocoanut palms, and forest trees now covers the old lava, while coarse grass grows rankly over the ash slopes of the crater. The torrential rains of the wet season from November to March
have cut three ravines down the slopes, and in former times, before the coral reef grew seaward to protect the island, the sea commenced to cut into the shores, forming a precipice about 20 feet high along the southeastern side of the island.
But, after the volcanic fires had ceased, corals began to grow along the shores and soon the island was surrounded by a fringing reef. The steep seaward slope and outer edges of this reef provided the best foothold for the growth of corals, and no sooner did the old ones die than new growths took possession of the coveted space and thus the reefs pushed seaward from the shores and the old volcano was protected from the attack of the breakers which now break impotently upon the outer edge of the ever-widening reef.
As is always the case under these conditions, the reef advanced seaward most rapidly against the wind, for corals thrive best in agitated water which is free from silt. Thus the reefs are three times as wide on the southeastern as on the northwestern sides of the island, for not only is the water too calm for the most luxuriant coral growth on the leeward side, but the mud which is washed over the reef-flats during the rainy season interferes seriously with coral growth. It is due also to this fact that the reef—or platform—is narrow wherever the silt from the streams washes over it, and wide wherever it is covered with pure ocean water and exposed to the full force of the breakers.
Maër Island is oval, about three miles long and one and a half wide and the southeast trade-wind causes the water currents to sheer in opposite directions from the middle of the southeast shore, and eddies are formed at both ends of the island, and these deposit water-washed sand along the leeward side, thus forming dunes at the ends and a sand beach along the middle of the leeward side, and converting the originally oval shape of the island into a crescent with its horns and concavity directed down the wind. Indeed Hedley and Griffith-Taylor, and Wood-Jones have shown that the crescentic shapes of coral atolls are formed in this manner in obedience to the direction of the prevailing winds and currents.
In short, the width and character of the reefs surrounding Maër Island are determined by the shore conditions; and it is quite clear that the island has not developed in the midst of a preexisting reef-flat, but that the volcano was formed before the modern reefs began to grow around it. Moreover, they are all fringing reefs that have grown outward from the shore and thus the "lagoon" of the great southeast reef is only 18 inches deep and its bottom is of hard coral with none of the mud and occasional reef patches seen in the bottoms of all lagoons between barrier reefs and the shore.
Indeed according to a theory which has been put forth by Penck, and more recently by Professor R. A. Daly, barrier reefs originated in a manner quite different from that of the recent fringing reefs of the Murray Islands. According to these students water was abstracted from the sea to form the great polar ice caps of the glacial epoch, and Professor R. S. Woodward has demonstrated mathematically that a still further lowering of level in tropical seas must have resulted from the attraction of the ice caps for the ocean surrounding them.
Thus the level of the tropical oceans may have been about 120 feet lower than at present. Now under these conditions the oceans would wash away the shores forming platforms along the tropical coasts at a level which would be about 120 feet below the present surface of the water.
Then when the ocean began again to rise, after the close of the glacial epoch, corals would grow along the outer edges of these platforms and thus Atolls and Barrier Reefs have been formed; the Atolls growing upon the truncated summits of mountains.
Andrews called attention to the fact that the platform upon the outer edge of which the Great Barrier Reef has grown, extends southward far beyond the latitude of corals, and Vaughan has observed that the platform of the Florida reef extends far northward beyond the last coral reefs. Also we may observe the Barrier Reef platform extends northward to the coast of New Guinea although the corals are killed in the wide region of the Bligh Entrance by the silt of the Fly and other great Papuan rivers. Thus it appears that the corals have merely grown as break-waters upon the seaward edges of platforms which were formed before the reefs themselves developed.
In some respects, the Pacific reefs are markedly different from those of the Atlantic. In the Pacific, one misses the beautiful sea fans and gorgonians that wave in languid grace to the rhythm of the surges in the crystal waters of Florida and the Bahamas. Instead, we find large areas of leathery-looking alcyonaria, or fleshy eight-rayed corals, Sarcophyton and Alcyonium, and in the crevices one often sees the giant clams Tridacna, their valves opened to show the beautiful mantle edges of malachite green, or blue, yellow or mottled with brown in a gamut of color, no two individuals being alike.
There are almost twice as many kinds of corals in the Pacific as in the Atlantic, and some of the more fragile of these grow luxuriantly down to depths of 60 feet or more, whereas in the Atlantic the coral reefs thrive well only in shallow water not over 20 feet in depth.But the most striking feature which distinguishes the Pacific reefs is the development of a ridge which actually projects half a foot or more above low tide level and extends along the outer seaward edge of the reef-wall wherever the breakers dash. In the Paumotos, this ridge is dull reddish pink in color, and it is composed of a mass of stony seaweeds or nullipores of the sort called Lithothamnion, and also of
bryozoa which are remarkable lime-secreting organisms related more closely to the worms than to any other phylum of the animal kingdom.
This lithothamnion ridge thrives only where the breakers strike in full force upon its living barrier, and it serves as the chief protector of the island, breaking the force of every wave that approaches the windward shore.
Clustered in the tide pools of this lithothamnion ridge, with the waves dashing constantly over them one finds living corals which cling tenaciously to the shallow crevices and grow into thin encrusting forms instead of into dome-like shapes as in more protected waters; or their branches are remarkably short stump-like and gnarled and tend to bend inward toward the shore after the manner of the ragged trees that survive along a wind-swept coast.
At Maër Island, the lithothamnion ridge extends along the extreme outer edge of the southeastern reef between 1,800 and 2,200 feet from shore, and it forms a veritable dam which prevents the escape of the water from the basin of the reef-flat at the lowest tides, so that at the low tide of the springs, one finds here a great shallow marine lake about 1,700 feet wide, 22 miles long, and only about 18 inches deep.
About 3,600,000 coral heads grow upon the hard rocky bottom of this natural aquarium, and in the middle region of the reef-flat, 1,000 feet from shore, fully 50 per cent, of the bottom is covered with heads the dominant species being the delicate and profusely branched Seriatopora histrix which forms a veritable coral forest, growing so luxuriantly that no other species can thrive so well in this region as it does nearer shore or farther out upon the reef. It is evident that there is a struggle for existence between the different sorts of corals, and the Seriatopora wins in this strife for place in the region 1,000 feet from shore. It is, however, very sensitive to high temperature, and the warm shallows close to shore are fatal to it so it can not survive within 550 feet of the beach. Also, being very slender, it can not survive the rush of the breakers and, thus it disappears about 1,670 feet out from shore where the surges shatter its fragile stems. Delicate and sensitive to high temperature, to silting, and to agitated water as it is, however, if conditions be ideal for its existence, it thrives so well that all other corals, even those that can live anywhere over the reef-flat, must give way to it.
The amount of food required to support the vast coral population of this reef-flat must be very great, especially, as Dr. Vaughan discovered, corals are strictly carnivorous and will not even attempt to capture plants. The minute floating animal life of the ocean is therefore the chief source of food for corals. Moreover, Dr. Vaughan showed that it is possible at a glance to tell the difference between a fat-looking, well fed coral and the thin, drawn appearance of a starved one. The corals of the southeast reef of Maër Island, however, all seem to be well fed, and thus it appears that the question of food has little or nothing to do with their struggle for existence.
There are, however, no large heads upon this reef, only a vast array of small ones.
Now the Murray Islands are in a fortunate region which is never visited by hurricanes, and thus the corals grow on for ages undisturbed by severe storms. Along the entire southeast beach only two small coral heads were found tossed ashore by the waves, a striking fact in contrast with the great heaps of dead coral ten feet high, found strewn along the shores of the Paumotos Islands where severe hurricanes occur.
Pocillopora damicornis. The fragile specimen on the right grew in the calm waters of the reef flat. The rigid one on the left grew in a tide pool among the breakers. Murray Islands, Torres Straits.
Bridal Veil Falls, Gavett's Leap, in the Blue Mountains of New South Wales, showing the characteristic block faulting seen along this part of the Australian coast.
There are, however, parts of the Great Barrier Reef region which are afflicted periodically by hurricanes and the reefs in these regions consist of large coral heads quite far apart instead of great numbers of small ones close together. Moreover, the pure ocean water of the Murray Islands is fairly free from silt, whereas that of Thursday Island bears a vast amount of mud in suspension and this, also, is fatal to corals and buries the small heads more readily than the large, and thus the reefs of Thursday Island are not rich, but the coral heads are of large size and are widely separated.
It is interesting to see how the 40 or more species of corals that grow upon the southeast reef-flat are distributed, and in order to gather a census of the corals, a line was surveyed across the reef, and at intervals of 200 feet, squares of 50 feet on the side were staked off and all the coral heads on each square were counted.
The shallows within 350 feet of the shore lack corals, the bottom being covered with a thin layer of limestone mud which supports a vigorous growth of a short-bladed eel grass, Posldonia australis.
On the square whose center was 400 feet from shore, only three small coral heads were found, and these were growing upon loose corroded limestone blocks which had been washed shoreward from the outer parts of the reef-flat. As one goes outward, however, the coral heads steadily increase in number becoming a maximum at 1,425 feet from shore where there were 1,838 coral heads on the square. Even the crest of the lithothamnion ridge 1,750 feet from shore had 201 living coral heads clinging to the bottom of its shallow tide pools, although the ridge itself was here fully six inches above the level of the lowest tides.
There must be some cause for this tendency on the part of the corals to grow best at considerable distances from shore. The truth of the matter is that corals are very sensitive to changes of temperature and an ocean as cold as 56° or as warm as 98° F. would be fatal to all the reef-building forms. The more delicate corals such as the finelybranching Seriatopora or the "stag horns," formerly known as Madrepora
but now called Acropora, are killed at 97.5°, and cease to take food at about 90.5° while the more resistant forms such as various species of Siderastrea, and Porites and some of the brain corals, survive to 100°. or even 102° F., but cease to feed at from 95° to 97.5° F. Now, in general, those corals which are most sensitive to high temperature are correspondingly so to the smothering effects of silt. The more delicate forms such as Acropora, Pocillopora and Seriatopora are killed by being buried for only 10 to 1-i hours beneath the mud, whereas, those corals which die at 100° can withstand as much as 40 to 50 hours of burial and Siderastrea radians of the Atlantic, which dies at 102°, can survive being buried 72 hours without apparent injury. It seems, therefore, that high temperature may produce death by causing asphyxiation, and thus those corals which can withstand the highest temperature are usually those which are best able to resist being covered by mud and silt, and these are the very corals which live in the hot, muddy shallows near the shore, while corals which require pure water live far out upon the reef, where the temperature is lower.
It will be recalled that Winterstein who studied frogs decided that the nervous paralysis that results from high temperature was caused by asphyxiation; but later Babàk, and Amerling showed that some of the frogs and toads are very resistant to lack of oxygen but easily paralyzed by heat, while the reverse is the case with others. Becht also casts doubt upon the asphyxiation theory by showing that recovery from heat paralysis can take place in the absence of oxygen in the water surrounding the nerves of the frog or of the horse-shoe crab (Limulus). Oxygen may however have been derived from the tissues themselves.
Among corals we find that Favia fragum and Mæandra areolata are more resistant to the effects of CO2 or of silt than one would expect from their death temperatures, which are fairly low. If however they be buried in the sand and then heated they are still nearly as resistant as if in the open water, whereas sensitive corals such as Acropora or Orbicella are killed at lower temperatures if buried than if heated in the open water.
The explanation may be that Favia and M. areolata can survive at a low as well as at a high rate of metabolism, in other words "hibernate" under the mud; and thus be almost as well able to resist heat in this condition as when living at a higher rate of oxygen-consumption in the free water of the ocean.
We still incline to the belief, therefore, that high temperature may produce death in corals by asphyxiation, although other factors may complicate the matter, as is so often the case in physiological reactions.Vaughan, indeed, has shown that those corals which live in muddy regions are quite able to free themselves from silt by means of the cilia which cover their surfaces, but those forms which live in the pure water of the outer parts of the reef are not so efficient in this respect.
We saw that there is evidence of a struggle for existence between the various kinds of corals, and according to Darwin's theory, we would expect this to have improved the corals. The Australian forms must withstand a very high temperature during the calm, hot days of the "northwest" season, while those of Florida must suffer annually from cold "northers." Yet, our experiments show that the Australian corals are quite as sensitive to high temperature as are those of Florida, and conversely the Florida corals can not withstand cold any better than can those of tropical Australia. In other words, natural selection has not improved the heat-resisting or cold-withstanding powers of the corals and yet temperature is a factor of primary importance in determining the life or death of reef corals. Of late years we have been steadily losing respect for the efficacy of natural selection as a means of developing morphological or physiological adjustments.
We must conclude that "corals are corals," and their behavior is essentially alike both in Florida and in Australia.
As we have seen, the "lagoon" of the reef flat on the southeast side of Maër Island is shallow, being only about 18 inches deep at the lowest tide, although covered by about 8 feet of water at high tide. When the low tide falls at the hottest part of the day, at about 3 o'clock in the afternoon, the water of the reef flat is several degrees warmer than the air, but in the early morning before sunrise, the water is always colder than the air. This shows that the lagoon water derives most of its heat during the day from direct solar radiation, and at night the surface of the water radiates heat into outer space and thus becomes colder than the air. It has been commonly supposed that the temperature range of ocean water is less than that of the air, but this is evidently not the case in shallow lagoons in the tropics where the range in air temperature is slight. Indeed, during five weeks in September and October at the Murray Islands, the difference in air temperature between the hottest day and coolest night was only 10° F., the hottest being 86° and the coolest 76°; but during the same time the water over the southeast reef-flat
ranged through 21°; the hottest being 93° and the coolest 72° F. Thus the reef-flat corals must be able to withstand a considerable range in temperature.
In the Pacific, the lithothamnion ridge always grows along the seaward face of reefs, provided the reef is exposed to the breakers, for the lithothamnion can thrive only in strongly agitated water. This ridge at Maër Island is only about six inches above low tide, for the breakers are not very high, the force of the rollers being partially spent upon the reefs of the Great Barrier six miles to the eastward of the Murray Islands.
We saw that at low tide the southeast reef flat of Maër Island is a wide shallow lake dammed in by the lithothamnion ridge. Now as the reef grew seaward this lithothamnion ridge always remained as a narrow boundary wall upon its advancing edge.
Thus in former times when the reefs began to grow outward, the lithothamnion ridge must have been close to the shore, whereas now it is from 1,800 to 2,200 feet out to sea. The lagoon behind this ridge is about eighteen inches deep and it is evident that as the reef advanced outward the shoreward edge of the lithothamnion ridge must have disintegrated or dissolved and has thus disappeared. Indeed, the disintegration of the dead inner edge of the lithothamnion ridge is very apparent in its ragged outline and the many loose blocks which are detached from it and washed shoreward, the process of disintegration being accelerated by the boring of numerous echinoderms; and it is evident that in same manner, a thickness of about two feet of limestone has disappeared so that the bottom of the present lagoon is now about eighteen inches below the crest of the lithothamnion ridge.
Sir John Murray and Alexander Agassiz believed that limestone was dissolved by sea water, but Dr. T. Wayland Vaughan collected samples of water from the lagoon of Tortugas, Florida, for an entire month and these were analyzed by Mr. R. B. Dole, who decided that they contained no free carbon dioxide. Now, without carbonic acid, or some other free acid, sea-water can not dissolve limestone.
The Tortugas is peculiar in being surrounded by wide areas of chalky mud and, moreover, the surface waters of the Florida-Bahama contain, according to Drew and Kellerman, great numbers of bacilli which cause a precipitation of calcium carbonate composed of such minute colloidal particles that they float for some time before sinking to form the impalpable limestone ooze of the sea bottom, and, finally, to change into oolite in the manner explained by Linck and by Vaughan, oolite being a rock composed of small calcium carbonate balls causing it to resemble fish roe.
One might expect therefore that the excessive amount of calcium carbonate in the water would hold the carbon dioxide in chemical combination, but Dr. Shiro Tashiro working with his marvelously sensitive bromites, finds that carbon dioxide is set free, and discharged into the air, from the Tortugas sea-water at ordinary atmospheric pressures and temperatures. The whole question as to the condition of the carbon dioxide within the ocean itself is therefore thrown open to be determined by future researches. It is still possible, however, that the seawater of Florida can not dissolve limestone and if this be true, the lagoons of the Florida-Bahama region were not formed by marine solution; but as yet no direct tests have been made to determine the efficacy of the water of the reefs as a limestone solvent, although the writer has begun a series of experiments to test this at Tortugas.
It seems that the limestone of the shallow southeast reef-flat of Maër Island must dissolve, for the disintegrated coral sand disappears in situ, there being very little sand either on the hard, rocky bottom of the lagoon or on the beach.
There are, however, several factors other than sea-water which might cause such solution, for it is well known that when rain-water percolates through dead leaves it gains a considerable charge of carbonic acid and this has been the cause of the solution which has resulted in the formation of the numerous caverns seen in all limestone regions. It is evident that the torrential rains of the wet season at Maër Island cause a great outpouring of fresh water from the shores over the reef flat and this must dissolve the limestone. This is not necessarily injurious to the living corals, however, for experiments made at Maër Island show that all species can survive being in sea-water diluted with an equal volume of rainwater for at least four and a half hours, and most of the forms can survive twelve hours of such treatment. The fact that there is but little coral sand along the southeast beach indicates that after it is cast ashore it is soon dissolved by the terrestrial drainage in the wet season.
There are, also, other agencies which dissolve limestone, for Professor Treadwell finds that worms which form burrows in dead coral heads are decidedly acid, and many sponges and boring plants are well known to dissolve the shells of molluscs. In addition, Stanley Gardiner, Wood-Jones, and others have observed that echinoderms which swallow large amounts of calcareous sand probably dissolve a certain percentage of it in their digestive tracts. We thus see that limestone is built up by some agencies and destroyed by others and the resultant condition of the reefs represents the balance between these antagonistic tendencies.This leads us to the question of the rate of growth of corals, a subject which has been studied in greatest detail by Dr. Vaughan at Tortugas, Florida, and in the Bahamas, but upon which many other students have worked in a less exhaustive manner. For example, in 1890, Saville-Kent measured and photographed certain corals off Vivien Point, Thursday Island, and some of these we succeeded in identifying and remeasuring in November, 1913, and it appeared that a brain coral, Symphyllia, which
was 30 inches in diameter in 1890 had increased to be 74 inches in 1913. Also, a huge coral which Saville-Ivent called "Porites astræoides" was 19 feet in diameter in 1890 and 22 feet and 92 inches in 1913. On the other hand, a certain gray-green Gonaistrea, which was 8 feet, 2 inches wide in 1890 had not grown during the intervening 23 years. Indeed, Dr. Vaughan's growth experiments upon Florida corals show that perhaps all corals grow to well-defined sizes and then cease to enlarge. However, the corals that did grow at Vivien Point had increased in diameter from 44 to 452 inches in 23 years, or about 1.9 inches per annum.
Thus charts of channels which are only occasionally used, and the bottoms of which are covered with corals, should, state that an upward growth of at least one inch per annum may be expected.
But other studies apart from those upon coral reefs were conducted at the Murray Islands. Dr. Hubert Lyman Clark, of Harvard, found many species of the delicate feathery "sea lilies" or crinoids, which live among the coral heads below low tide. These crinoids were, by some, supposed to be sedentary animals but Dr. Clark found that at least certain forms can swim actively through the water using their long graceful arms as oars. In cretaceous times crinoids were abundant along our own shores but are now common only in the depths of the Atlantic Ocean and in the shallow water of the western tropical Pacific and Malayan region northward to Japan.
There were also great numbers of slender serpent stars, rapidly moving forms which usually live in crevices among the rocks and scuttle off
with great rapidity when disturbed. They are often called "brittle stars," for if one seizes an arm it is promptly cast off, permitting the major portion of the animal to escape. Their beautiful sculpturing, rich colors, and the ornate patterns of their disks were admirably figured in color by Mr. E. M. Grosse, who executed more than 100 beautiful drawings which will serve to illustrate Dr. Clark's purposed paper upon the Echinoderms of Torres Straits. Indeed, Dr. Clark aptly called the region "a paradise for echinoderms," and it appears to be the richest known locality in the world for shallow-water forms of these animals, for Dr. Clark found 51 species at Maër Island alone, and in addition, he collected 26 others at Badu, Darnley and Thursday Islands; making 177 from Torres Straits. Thus his collection is a notable addition to that of the Museum of Comparative Zoology at Harvard, which was probably already the greatest gathering of specimens of echinoderms in the world. In almost every instance Mr. Grosse's figure is the only colored drawing of these Torres Straits species, and thus Dr. Clark's paper will be a classic upon the subject of tropical Pacific echinoderms.
117 species had been previously recorded from Torres Straits, and of these, Dr. Clark found only 42, but in addition he found at least 45 not previously known to science, so that at present fully 250 echinoderms are known from this extraordinary region.
As is well known to physiologists, the important subject of the penetration of living cells by alkalies has for several years engaged the attention of Dr. E. Newton Harvey, of Princeton, and his results essentially support Overton's lipoid theory, namely, that those substances which are most readily dissolved in fat-solvents enter living cells most readily; and this leads one to suspect that the cell surface may be lipoid, or fat-like in nature.
No one had been able to test this hypothesis for acids, until Dr. Harvey discovered a holothurian at the Murray Islands, Stycopus ananas, the intestines of which are purplish-red. If placed in acid, however, they turn bright red, and in alkalies dark purple; and these changes are reversible and may take place in weak acids or alkalies without killing the cells. Dr. Harvey used 24 different kinds of acids in dilute solutions upon this animal and found that those which are most poisonous penetrate most rapidly, and all the acids penetrate about in the ratio of their degree of toxicity. There is, on the other hand, no relation between the degree of dissociation of an acid and its rate of penetration of the living cells; and there is only a fair but by no means perfect agreement between the rate of penetration and the solubility of an acid in xylol.
Overton's theory applies, however, with the majority of acids, but the agreement is not perfect, and hence Harvey concludes that the power of penetration of an acid depends not only on its lipoid solubility but also upon the affinity of the acid for certain protein substances of the cell surface.
Mr. Frank A. Potts, of Trinity Hall, Cambridge University, reports that he found at the Murray Islands a small lobster-shaped crustacean called Alpheus which lives among the arms of crinoids and usually resembles the rich brown or mottled color of its host. Upon examining some of these Alpheus, Mr. Potts noticed numerous small pink sac-like bodies attached to their legs and these sacs contain the eggs and young larvæ of a barnacle-like animal which is evidently a parasite infesting the Alpheus. In fact this degenerate barnacle grows within the tissues of the Alpheus, and losing all semblance to a crustacean, changes into a mass of root-shaped branches which at intervals send out sac-like genital organs, these being the only special organs it possesses. When the Alpheus moults, the sacs are cast off and each little larva is doubtless liberated to wander for a time as a free-swimming minute crustacean and finally to find an Alpheus and to enter its body and change into a root-like parasite, losing its eyes, legs, antennules, and all organs of special sense to grow into a mere root-like form which sends out its genital sacs upon the legs of its unfortunate host. The name of this very degenerate creature is Thylacoplethus.
Another curious animal which attracted the attention of Mr. Potts was a crab called Hapalocarcinus, the female of which settles down while still very small and immature among the branches of the Pocillopora coral. Here the breathing of the crab produces a water current and this causes the branches of the coral to thicken and finally to enclose the crab in a capsule, leaving only a small aperture far too small to permit of its escape, but large enough to admit the minute male of the species who visits the chamber at the time the female moults.
Professor David Hilt Tennent, of Bryn Mawr College, while at the Tortugas Laboratory in Florida, discovered that the hybrid larvæ of certain echini can be caused to resemble either their father or their mother in response to definite changes in the alkalinity of the seawater. The cytology of this matter has attracted much attention and discussion, and Professor Tennent went with us to the Murray Islands to continue studies of similar import and to study other hybrid crosses between echinoderms.
He caused an artificial cross to occur between a crinoid and an echinus and carried the larvæ farther than had previously been done.
Some of Professor Tennent's best studies were carried out upon Badu Island where members of the expedition enjoyed the privilege of being the guests of the Reverend F. W. Walker, the able managing director of the "Papuan Industries, Limited," which is devoted to developing arts and crafts among the natives thus to enable them to become self-supporting in the broad civilized sense of the term, and to restore that self respect and interest in life which the too sudden introduction of civilization has in large measure crushed out among them. Interesting and hopeful results are being achieved by this sociological, rather than purely religious, enterprise. The natives must first learn how to earn a living before they can make any real advance in the development of a moral and social standard to which they can hold as things of their own initiation. At present a mere semblance of civilization has been forced upon them from outside, but a race to survive must be the father of its own ideals.
After leaving the Murray Islands, Mr. Potts and the leader of the expedition went to Port Moresby, Papua, where His Excellency, the Honorable John H. P. Murray, the governor, was so kind as to invite us to be his guests at Government House during the entire period of our visit.
The English deserve the greatest credit for the altruistic government which is being administered to benefit and uplift the native population. "Fair play for the Papuan" is the watch-word of the colony.
Malaria is still the dreaded pestilence of Papua, and for generations yet to come many noble English lives must be extinguished by its ravages, but despite the dull heat, the certainty of ennervating illness, and the vast areas yet unknown to any save the savage in the stone age, this little band of high-minded men has not lost heart but year by year intertribal wars, cannibalism and sorcery are becoming things of the past, and the natives are slowly but willingly acquiring their first lessons in civilization.
Without detracting from the honor due the missionary who leaves home and friends and seeks the degraded places of the earth, let us not forget the equally altruistic civil servant whose hardships and dangers and devotion to duty we are all too apt to belittle or overlook, yet whose service though less conspicuous than that of his religious co-worker is equally significant for the raising of England's standard of freedom before the eyes of the whole earth.