CORAL 



CORAL FISHES 



473 



rising of the reef keeping pace with tin- sinking of 

 tin- ^c.i liMttom. TliUH by-and-bv the fringing- reef 

 i-, ( -iui> -i-rii-d into a barrier- reef. \Ve have im\v only 

 to suppose that the movement of subsidence ami 

 the labours of the corals continue until the reef- 

 enriivl'-d island disappears below the waves, and a 

 complete atoll will oe the final result. Darwin's 

 virus \\vre illustrated and strongly supported by 

 I'M 'tensor J. D. Dana, who accompanied the Wilkes 

 exploring expedition round the world in 1838-42, 

 while MM. Couthouy and Beete Jukes likewise 

 upheld i IK- hypothesis of subsidence. The re- 

 searches of Professors L. Agassiz and Le Conte 

 amongst the reefs of Florida have shown that 

 l;u win's views are there inapplicable. They 

 attribute the formation of the southern portion 

 of Florida, which consists of a series of concentric 

 barrier-reefs, to the natural growth of the coral 

 alone aided by the mechanical action of the sea 

 a view which, stated generally, is the same as that 

 held by Chamisso. Professor Karl Semper like- 

 wise, after examining the reefs of the Pelew Islands, 

 came to the conclusion that the form of these reefs 

 had been determined by the natural growth of the 

 corals, modified by local conditions, which is just 

 Chamisso's explanation. But Darwin had already 

 expressly stated that some reefs might have origin- 

 ated in the manner suggested by Chamisso ; and 

 geologists apparently recognised that the conditions 

 of the great Florida reef were hardly analogous to 

 the isolated atolls which rise from profound depths 

 in the open ocean. 



In 1880, however, Dr (afterwards Sir) John 

 Murray of the Challenger expedition, published 

 another explanation which has given rise to con- 

 siderable discussion. He returns to the old views 

 of Chamisso, maintaining that reefs have grown up 

 from the tops of submerged and partially sub- 

 merged banks and mountains. To the objection 

 that it is hard to believe that so many banks and 

 cones should occur just at the proper depth from 

 the surface, Dr Murray replies that it is not 

 necessary to suppose that all the submarine emin- 

 ences were of equal or nearly equal height. Some 

 may have risen at first above the level of the sea, 

 and subsequently have been reduced by the waves 

 and breakers to the condition of shoals ; while 

 others that did not reach to the limits within which 

 reef-builders live may have been brought up to that 

 zone by the accumulation upon them of the hard 

 parts of pelagic organisms. For these forms of life 

 flourish in extraordinary numbers in the surface- 

 waters of the tropics where reefs abound, and as 

 they die, their hard parts falling to the bottom will 

 accumulate there along with the exuviae of creatures 

 living at such depths, until they come to form con- 

 siderable deposits. This levelhng-up of submarine 

 banks to the zone within which coral-builders 

 thrive is the most marked feature in Dr Murray's 

 hypothesis. His further account of the mode in 

 which atolls and barrier-reefs have been formed is 

 a more particular and scientific development of 

 Chamisso's explanation. The growth of a reef is 

 regulated by the food-supply of the corals ; those 

 growing on the external parts of the reef are most 

 favourably placed in this respect, consequently 

 they thrive best, and have the advantage over those 

 that are growing in the centre of the reef ; and this 

 (lillei-ence in the rate of growth of the outer and 

 inner areas will be intensified as the reef approaches 

 the surface. Eventually the corals of the interior 

 die, and the dead coral rock is gradually removed 

 by the solvent action of the sea- water which 

 contains carbonic acid. In this manner the 

 reef assumes a basin-shaped form. F ringing-reefs, 

 according to Dr Murray, are converted into barrier- 

 reefs by the simple outward growth of the coral 

 anon a talus of its own debris, forced off from the 



edge of the reef by the breakers. The lagoon - 

 channel that eventually separates the reef from the 

 land is formed in the same way as the lagoon of an 

 atoll namely, by the dissolution and removal of 

 dead coral rock. Professor A. Agaturiz publinhed 

 in 1882 an account of bin ill-tailed examination of 

 the Tortugas and the Florida reefs, in which he 

 shows how the bottom of the sea in those regions 

 has been gradually raised by the accumulation of 

 the exuviie and skeletons of massive organisms 

 which flourish in prodigious numbers on the sea- 

 floor, forming the submarine plateaus known a* the 

 Florida, Yucatan, and San Pedro banks. He thinks 

 it is by the gradual upward growth of such accumu- 

 lations that the sea-bottom was eventually rained 

 to the zone in which reef-builders thrive. He thus 

 arrived independently at the same general con- 

 clusion as Dr Murray. 



As recently as 1887 Dr Guppy (q.v.) has given 

 the result of his investigations in the Solomon 

 Islands, and has vigorously supported the hypo- 

 thesis advocated by Murray. He shows that in 

 those islands we have elevated reefs which exhibit 

 the very structure which we should expect to 

 find if the new view of coral-reef structure i 

 correct. He found some of those islands largely 

 composed of earthy calcareous deposits having the 

 same character and origin as the various volcanic 

 muds and organic oozes which the Challenger 

 expedition dredged at depths varying from 100 to 

 2000 fathoms. These deposits reached to heights 

 of over 1000 feet, and in some cases denudation had 

 exposed an underlying nucleus of volcanic roclc. 

 The earthy calcareous beds were covered with a 

 comparatively thin crust of true coral rock. The 

 phenomena described by Dr Guppy thus lead to the 

 belief that many other atolls may have a similar 

 structure. Dr Guppy thinks that the various 

 agencies insisted upon by Semper, Murray, and A. 

 Agassiz such as currents and tidal scour, solution 

 and the distribution of food-supply, the repressive 

 influence of sediment and the action of the 

 breakers have each played a part in determining 

 I the form of coral reefs. To the objection that 

 some lagoons are deeper than the zone in which 

 reef-corals live, Dr Guppy replies that where the 

 submarine slope is moderate, the water clear, and 

 breakers of no great size, reef-corals may be found 

 flourishing at depths of 50 and even 60 fathoms. 

 Whether the explanation advocated by Murray and 

 Guppy is destined to lead to the total collapse of 

 Darwin's hypothesis, is likely to remain for some 

 time an unsettled question some writers holding 

 that while Murray's view may be the true explana- 

 tion of the origin of many atolls and barrier-reefs, 

 it does not forbid the possibility or, as others would 

 say, the probability that many other reefs may 

 really have been formed, as Darwin supposed, dur- 

 ing slow subsidence of the bottom. 



See CiKl.KNTKKATKS, ANEMONE, ALCTONIUM ; text- 



books of Zoology Huxley, Glaus, Ac. ; Darwin, Dana, 

 Murray, Guppy, <!tc. on Coral-reefs, and Seiuper's Animal 

 Life; Moseley and Quelch Challenger Rep., vols. ii and 

 xvi. ; for skeleton, Von Koch, Morphologitchn Jahrbuch 

 (1879-86); for red coral, Lacaze-Duthiere, Hittoire 

 Naturelle du Corail (1864); for fossil forms, Zittel's 

 Palaontologie ; systematic works Dana, Zoophyte* 

 (1848-49); Milne-Edwards and Haime, HiL Nat. det 

 Coralliares (1867-60); Koren and Danielssen, Nye 

 Alcyonider, Oorgonider og Pennatulider (1883); Koch, 

 Monograph on Qoryonida ( Naples Station, 1887 ). 



Coral Fishes (Squamipennes), a name applied 

 to a family of bony fishes in the spiny-rayed or 

 Acanthopterous order. They are tropical forms, 

 abundant about coral-reefs, usually small, with 

 short, deep, often brightly coloured bodies. The 

 family includes the Archer-fish (q.v.), the very 

 beautiful Chaetodons, the genus Chelmo with 



