animated coral stocks, there have been gradually established more
accurate views respecting the influence exercised by corals on other
departments of Nature,--on the elevation of groups of low islands
above the level of the sea,--on the migrations of land-plants and the
successive extension of the domains of particular Floras,--and, lastly,
in some parts of the ocean, on the diffusion of races of men, and the
spread of particular languages.
As minute organic creatures living in society, corals do indeed perform
an important part in the general economy of Nature, although they
do not, as was begun to be believed at the time of Cook’s voyages,
enlarge continents and build up islands from fathomless depths of
the ocean. They excite the liveliest interest, whether considered as
subjects of physiology and of the study of the gradation of animal
forms, or whether they are regarded in reference to their influence on
the geography of plants and on the geological relations of the crust
of the Earth. According to the great views of Leopold von Buch, the
whole formation of the Jura consists of “large raised coral-banks of
the ancient world surrounding the ancient mountain chains at a certain
distance.”
In Ehrenberg’s Classification, (Abhandlungen der Akad. der Wiss. zu
Berlin aus dem, J. 1882, S. 393-432) Coral-animals, (often improperly
called, in English works, Coral-insects) are divided into two great
classes: the single-mouthed Anthozoa, which are either free or capable
of detaching themselves, being the animal-corals, Zoocorallia; and
those in which the attachment is permanent and plant-like, being the
Phyto-corals. To the first order, the Zoocorallia, belong the Hydras
or Arm-polypi of Trembley, the Actiniæ decked with beautiful colours,
and the mushroom-corals; to the second order or Phyto-corals belong the
Madrepores, the Astræids, and the Ocellinæ. The Polypi of the second
order are those which, by the cellular wave-defying ramparts which
they construct, are the principal subject of the present note. These
ramparts consist of an aggregate of coral trunks, which, however, do
not instantly lose their common vitality as does a forest tree when cut
down.
Every coral-trunk is a whole which has arisen by a formation of buds
taking place according to certain laws, the parts of which the whole
consists forming a number of organically distinct individuals. In the
group of Phyto-corals these individuals cannot detach themselves at
pleasure, but remain united with each other by thin plates of carbonate
of lime. It is not, therefore, by any means the case that each trunk of
coral has a central point of common vitality or life. (See Ehrenberg’s
Memoir above referred to, S. 419.) The propagation of coral-animals
takes place, in the one order, by eggs or by spontaneous division; and
in the other order, by the formation of buds. It is the latter mode of
propagation which, in the development of individuals, is the most rich
in variety of form.
Coral-reefs, (according to the definition of Dioscorides, sea-plants, a
forest of stone-trees, Lithodendra), are of three kinds;--coast reefs,
called by the English “shore or fringing reefs,” which are immediately
connected with the coasts of continents or islands, as almost all the
coral banks of the Red Sea seen during an eighteen months’ examination
by Ehrenberg and Hemprich;--“barrier-reefs,” “encircling-reefs,” as
the great Australian barrier-reef on the north-east coast of New
Holland, extending from Sandy Cape to the dreaded Torres Strait; and
as the encircling-reefs surrounding the islands of Vanikoro (between
the Santa Cruz group and the New Hebrides) and Poupynete (one of
the Carolinas);--and lastly, coral banks enclosing lagoons, forming
“Atolls” or “Lagoon-islands.” This highly natural division and
nomenclature have been introduced by Charles Darwin, and are intimately
connected with the explanation which that ingenious and excellent
investigator of nature has given of the gradual production of these
wonderful forms. As on the one hand Cavolini, Ehrenberg, and Savigny
have perfected the scientific-anatomical knowledge of the organisation
of coral-animals, so on the other hand the geographical and geological
relations of coral-islands have been investigated and elucidated,
first by Reinhold and George Forster in Cook’s Second Voyage, and
subsequently, after a long interval, by Chamisso, Péron, Quoy and
Gaimard, Flinders, Lütke, Beechey, Darwin, d’Urville, and Lottin.
The coral-animals and their stony cellular structures or scaffolding
belong principally to the warm tropical seas, and the reefs are found
more frequently in the Southern than in the Northern Hemisphere. The
Atolls or Lagoon Islands are crowded together in what has been called
the Coral-Sea, off the north-east coast of New Holland, including New
Caledonia, the Salomon’s Islands, and the Louisiade Archipelago; in
the group of the Low islands (Low Archipelago), eighty in number; in
the Fidji, Ellice, and Gilbert groups; and in the Indian Ocean, on the
north-east of Madagascar, under the name of the Atoll-group of Saya de
Malha.
The great Chagos bank, of which the structure and rocks of dead coral
have been thoroughly examined by Captain Moresby and by Powell, is so
much the more interesting, because we may regard it as a continuation
of the more northerly Laccadives and Maldives. I have already called
attention elsewhere (Asie Centrale, T. i. p. 218), to the importance
of the succession of these Atolls, running exactly in the direction
of a meridian and continued as far as 7° south latitude, to the
general system of mountains and the configuration of the earth’s
surface in Central Asia. They form a kind of continuation to the great
rampart-like mountain elevations of the Ghauts and the more northern
chain of Bolor, to which correspond in the trans-Gangetic Peninsula the
North and South Chains which are intersected near the great bend of the
Thibetian Tzang-bo River by several transverse mountain systems running
east and west. In this eastern peninsula are situated the chains of
Cochin China, Siam, and Malacca which are parallel with each other, as
well as those of Ava and Arracan which all, after courses of unequal
length, terminate in the Gulfs or Bays of Siam, Martaban, and Bengal.
The Bay of Bengal appears like an arrested attempt of nature to form an
inland sea. A deep invasion of the ocean, between the simple western
system of the Ghauts, and the eastern very complex trans-Gangetic
system of mountains, has swallowed up a large portion of the low
lands on the eastern side, but met with an obstacle more difficult to
overcome in the existence of the extensive high plateau of Mysore.
Such an invasion of the ocean has occasioned two almost pyramidal
peninsulas of very different dimensions, and differently proportioned
in breadth and length; and the continuations of two mountain systems
(both running in the direction of the meridian, _i. e._, the mountain
system of Malacca on the east, and the Ghauts of Malabar on the west),
shew themselves in submarine chains of mountains or symmetrical
series of islands, on the one side in the Andaman and Nicobar Islands
which are very poor in corals, and on the other side in the three
long-extended groups or series of Atolls of the Laccadives, the
Maldives, and Chagos. The latter series, called by navigators the
Chagos-bank, forms a lagoon encircled by a narrow and already much
broken, and in great measure submerged, coral reef. The longer and
shorter diameters of this lagoon, or its length and breadth, are
respectively 90 and 70 geographical miles. Whilst the enclosed lagoon
is only from seventeen to forty fathoms deep, the depth of water at a
small distance from the outer margin of the coral, (which appears to be
gradually sinking), is such, that at half a mile no bottom was found
in sounding with a line of 190 fathoms, and, at a somewhat greater
distance, none with 210 fathoms. (Darwin, Structure of Coral Reefs, p.
39, 111, and 183.) At the coral lagoon called Keeling-Atoll, Captain
Fitz-Roy, at a distance of only two thousand yards from the reef, found
no soundings with 1200 fathoms.
“The corals which, in the Red Sea, form thick wall-like masses, are
species of Meandrina, Astræa, Favia, Madrepora (Porites), Pocillopora
(hemprichii), Millepora, and Heteropora. The latter are among the most
massive, although they are somewhat branched. The corals which lie
deepest below the surface of the water in this locality, and which,
being magnified by the refraction of the rays of light, appear to the
eye like the domes or cupolas of a cathedral or other large building,
belong, so far as we were enabled to judge, to Meandrina and Astræa.”
(Ehrenberg, manuscript notices.) It is necessary to distinguish between
separate and in part free and detached polypifers, and those which
form wall-like structures and rocks.
If we are struck with the great accumulation of building polypifers
in some regions of the globe, it is not less surprising to remark the
entire absence of their structures in other and often nearly adjoining
regions. These differences must be determined by causes which have not
yet been thoroughly investigated; such as currents, local temperature
of the water, and abundance or deficiency of appropriate food. That
certain thin-branched corals, with less deposit of lime on the side
opposite to the opening of the mouth, prefer the repose of the interior
of the lagoon, is not to be denied; but this preference for the
unagitated water must not, as has too often been done (Annales des
Sciences Naturelles, 1825, T. vi. p. 277), be regarded as a property
belonging to the entire class. According to Ehrenberg’s experience in
the Red Sea, that of Chamisso in the Atolls of the Marshall Islands
east of the Caroline group, the observations of Captain Bird Allen in
the West Indies, and those of Capt. Moresby in the Maldives, living
Madrepores, Millepores, and species of Astræa and of Meandrina,
can support the most violent action of the waves,--“a tremendous
surf,”--(Darwin, Coral Reefs, pp. 63-65), and even appear to prefer the
most stormy exposure. The living organic forces or powers regulating
the cellular structure, which with age acquires the hardness of rock,
resist with wonderful success the mechanical forces acting in the shock
of the agitated water.
In the Pacific, the Galapagos Islands, and the whole Western Coast of
America, are entirely without coral reefs, although so near to the many
Atolls of the Low Islands, and the Archipelago of the Marquesas. This
absence of corals might perhaps be ascribed to the presence of colder
water, since we know that the coasts of Chili and Peru are washed by
a cold current coming from the south and turning to the westward off
Punta Parina, the temperature of which I found, in 1802, to be only
12°.5 Reaumur (60°.2 Fah.), while the undisturbed adjacent masses of
water were from 22° to 23° Reaumur (81°.5 to 83°.8 Fah.); and there are
also among the Galapagos small currents running between the islands,
having a temperature of only 11°.7 Reaumur (58°.2 Fah.) But these lower
temperatures do not extend farther to the north along the shores of the
Pacific, and are not found upon the coasts of Guayaquil, Guatimala,
and Mexico; nor does a low temperature prevail at the Cape de Verd
Islands on the West Coast of Africa, or at the small islands of St.
Paul (St. Paul’s rocks), or at St. Helena, Ascension, or San Fernando
Noronha,--which yet are all without coral reefs.
While this absence of coral reefs appears to characterise the _western_
coasts of Africa, America, and Australia, on the other hand such reefs
abound on the _eastern_ coasts of tropical America, of Africa, on the
coasts of Zanzibar and Australia, and on that of New South Wales. The
coral banks which I have chiefly had opportunities of observing are
those of the interior of the Gulf of Mexico, and those to the south
of the Island of Cuba, in what are called the “Gardens of the King
and Queen” (Jardines y Jardinillos del Rey y de la Reyna). It was
Columbus himself who, on his second voyage, in May 1494, gave that
name to this little group of islands, because the agreeable mixture
of the silver-leaved arborescent Tournefortia gnapholoides, flowering
species of Dolichos, Avicennia nitida, and mangrove hedges, gave to
the coral islands the appearance of a group of floating gardens. “Son
Cayos verdes y graciosos llenos de arboledas,” says the Admiral. On the
passage from Batabano to Trinidad de Cuba, I remained several days in
these gardens, situated to the east of the larger island, called the
Isla de Pinos, which is rich in mahogany trees: my stay was for the
purpose of determining the longitude of the different keys (Cayos). The
Cayo Flamenco, Cayo Bonito, Cayo de Diego Perez, and Cayo de piedras,
are coral islands rising only from eight to fourteen inches above the
level of the sea. The upper edge of the reef does not consist simply
of blocks of dead coral; it is rather a true conglomerate, in which
angular pieces of coral, cemented together with grains of quartz, are
embedded. In the Cayo de piedras I saw such embedded pieces of coral
measuring as much as three cubic feet. Several of the small West
Indian coral islands have fresh water, a phenomenon which, wherever it
presents itself, (for example, at Radak in the Pacific; see Chamisso
in Kotzebue’s Entdeckungs-Reise, Bd. iii. S. 108), is deserving of
examination, as it has sometimes been ascribed to hydrostatic pressure
operating from a distant coast, (as at Venice, and in the Bay of Xagua
east of Batabano), and sometimes to the filtration of rain water. (See
my Essai politique sur l’Ile de Cuba, T. ii. p. 137.)
The living gelatinous investment of the stony calcareous part of the
coral attracts fish, and even turtles, who seek it as food. In the time
of Columbus the now unfrequented locality of the Jardines del Rey was
enlivened by a singular kind of fishery, in which the inhabitants of
the coasts of the Island of Cuba engaged, and in which they availed
themselves of the services of a small fish. They employed in the
capture of turtle the Remora, once said to detain ships (probably the
Echeneis Naucrates), called in Spanish “Reves,” or reversed, because
at first sight his back and abdomen are mistaken for each other. The
remora attaches itself to the turtle by suction through the interstices
of the indented and moveable cartilaginous plates which cover the
head of the latter, and “would rather,” says Columbus, “allow itself
to be cut in pieces than lose its hold.” The natives; therefore,
attach a line, formed of palm fibres, to the tail of the little fish,
and after it has fastened itself to the turtle draw both out of the
water together. Martin Anghiera, the learned secretary of Charles V.,
says, “Nostrates piscem reversum appellant, quod versus venatur. Non
aliter ac nos canibus gallicis per æquora campi lepores insectamur,
illi (incolæ Cubæ insulæ) venatorio pisce pisces alios capiebant.”
(Petr. Martyr, Oceanica, 1532, Dec. I. p. 9; Gomara, Hist. de las
Indias, 1553, fol. xiv.) We learn by Dampier and Commerson that this
piscatorial artifice, the employing a sucking-fish to catch other
inhabitants of the water, is much practised on the East Coast of
Africa, at Cape Natal and on the Mozambique Channel, and also in the
Island of Madagascar. (Lacépède, Hist. nat. des Poissons, T. i. p.
55.) The same necessities combine with a knowledge of the habits of
animals to induce the same artifices and modes of capture among nations
who are entirely unconnected with each other.
Although, as we have already remarked, the zone included between 22
or 24 degrees of latitude on either side of the equator, appears to
be the true region of the calcareous saxigenous lithophytes which
raise wall-like structures, yet coral reefs are also found, favoured
it is supposed by the warm current of the Gulf-stream, in lat. 32°
23´, at the Bermudas, where they have been extremely well described by
Lieutenant Nelson. (Transactions of the Geological Society, 2d Series,
1837, Vol. V. Pt. i. p. 103.) In the southern hemisphere, corals,
(Millepores and Cellepores), are found singly as far south as Chiloe,
the Archipelago of Chonos, and Tierra de Fuego, in 53° lat.; and
Retepores are even found in lat. 72-1/2°.
Since the second voyage of Captain Cook there have been many defenders
of the hypothesis put forward by him as well as by Reinhold and George
Forster, according to which the low coral islands of the Pacific have
been built up by living creatures from the depths of the bottom of
the sea. The distinguished investigators of nature, Quoy and Gaimard,
who accompanied Captain Freycinet in his voyage round the world in
the frigate Uranie, were the first who ventured, in 1823, to express
themselves with great boldness and freedom in opposition to the views
of the two Forsters (father and son), of Flinders, and of Péron.
(Annales des Sciences Naturelles, T. vi., 1825, p. 273.) “En appelant
l’attention des naturalistes sur les animalcules des coraux, nous
espérons démontrer que tout ce qu’on a dit ou cru observer jusqu’à
ce jour relativement aux immenses travaux qu’il sont susceptibles
d’exécuter, est le plus souvent inexact et toujours excessivement
exagéré. Nous pensons que les coraux, loin d’élever des profondeurs
de l’océan des murs perpendiculaires, ne forment que des couches ou
des encroûtemens de quelques toises d’èpaisseur.” Quoy and Gaimard
also propounded (p. 289) the conjecture that the Atolls, (coral walls
enclosing a lagoon), probably owed their origin to submarine volcanic
craters. Their estimate of the depth below the surface of the sea at
which the animals which form the coral reefs (the species of Astræa,
for example) could live, was doubtless too small, being at the utmost
from 25 to 30 feet (26-1/2 to 32 E.) An investigator and lover of
nature who has added to his own many and valuable observations a
comparison with those of others in all parts of the globe, Charles
Darwin, places with greater certainty the depth of the region of
living corals at 20 to 30 fathoms. (Darwin, Journal, 1845, p. 467; and
the same writer’s Structure of Coral Reefs, p. 84-87; and Sir Robert
Schomburgk, Hist. of Barbadoes, 1848, p. 636.) This is also the depth
at which Professor Edward Forbes found the greatest number of corals
in the Egean Sea: it is his “fourth region” of marine animals in his
very ingenious memoir on the “Provinces of Depth” and the geographical
distribution of Mollusca at vertical distances from the surface.
(Report on Ægean Invertebrata in the Report of the 13th Meeting of the
British Association, held at Cork in 1843, pp. 151 and 161.) The depths
at which corals live would seem, however, to be very different in
different species, and especially in the more delicate ones which do
not form such large masses.
Sir James Ross, in his Antarctic Expedition, brought up corals with
the sounding lead from great depths, and entrusted them to Mr. Stokes
and Professor Forbes for more thorough examination. On the west of
Victoria Land, near Coulman Island, in S. lat. 72° 31´, at a depth of
270 fathoms, Retepora cellulosa, a species of Hornera, and Prymnoa
Rossii, were found quite fresh and living. Prymnoa Rossii is very
analogous to a species found on the coast of Norway. (See Ross, Voyage
of Discovery in the Southern and Antarctic Regions, vol. i. pp. 334 and
337.) In a similar manner in the high northern regions the whalers have
brought up Umbellaria grænlandica, living, from depths of 236 fathoms.
(Ehrenberg, in the Abhandl. der Berl. Akad. aus dem J. 1832, S. 430.)
We find similar relations of species and situation among sponges,
which, indeed, are now considered to belong rather to plants than to
zoophytes. On the coasts of Asia Minor the common sponge is found by
those engaged in the fishery at depths varying from 5 to 30 fathoms;
whereas a very small species of the same genus is not found at a less
depth than 180 fathoms. (Forbes and Spratt, Travels in Lycia, 1847,
Vol. ii. p. 124.) It is difficult to divine the reason which prevents
Madrepores, Meandrina, Astræa, and the entire group of tropical
Phyto-corals which raise large cellular calcareous structures, from
living in strata of water at a considerable depth below the surface of
the sea. The diminution of temperature in descending takes place but
slowly; that of light almost equally so; and the existence of numerous
Infusoria at great depths shews that the polypifers would not want for
food.
In opposition to the hitherto generally received opinion of the
entire absence of organic life in the Dead Sea, it is deserving of
notice that my friend and fellow labourer, M. Valenciennes, has
received through the Marquis Charles de l’Escalopier, and also the
French consul Botta, fine specimens of Porites elongata from the
Dead Sea. This fact is the more interesting because this species is
not found in the Mediterranean, but belongs to the Red Sea, which,
according to Valenciennes, has but few organic forms in common with
the Mediterranean. I have before remarked that in France a sea fish, a
species of Pleuronectes, advances far up the rivers into the interior
of the country, thus becoming accustomed to gill-respiration in
fresh water; so we find that the coral-animal above spoken of, the
Porites elongata of Lamarck, has a not less remarkable flexibility of
organisation, since it lives in the Dead Sea, which is over-saturated
with salt, and in the open ocean near the Seychelle Islands. (See my
Asie Centrale, T. ii. p. 517.)
According to the most recent chemical analyses made by the younger
Silliman, the genus Porites, as well as many other cellular polypifers,
(Madrepores, Andræas, and Meandrinas of Ceylon and the Bermudas),
contain, besides 92-95 per cent. of carbonate of lime and magnesia,
some fluoric and phosphoric acids. (See p. 124-131 of “Structure and
Classification of Zoophytes,” by James Dana, Geologist of the United
States’ Exploring Expedition, under the command of Captain Wilkes.)
The presence of fluorine in the solid parts of polypifers reminds
us of the fluorate of lime in the bones of fishes, according to the
experiments of Morechini and Gay Lussac at Rome. Silex is only found
mixed in very small quantity with fluorate and phosphate of lime in
coral stocks; but a coral-animal allied to the Horn-coral, Gray’s
Hyalonema, has an axis of pure fibres of silex resembling a queue or
braided tress of hair. Professor Forchhammer, who has been lately
engaged in a thorough analysis of the sea-water from the most different
parts of the globe, finds the quantity of lime in the Caribbean Sea
remarkably small, being only 247 parts in ten thousand, while in
the Categat it amounts to 371 parts in ten thousand. He is disposed
to attribute this difference to the many coral-banks among the West
Indian Islands, which appropriate the lime, and lower the per centage
remaining in the sea-water. (Report of the 16th Meeting of the British
Association for the Advancement of Science, held in 1846, p. 91.)