﻿240 BULLETIN 103, UNITED STATES NATIONAL MUSEUM. 



Ecology op Reef-Forming Corals. 



This subject has received the attention of very many investigators, 

 and most of the broad principles have long been known. Darwin 

 clearly recognized the difference in growth-form of exposed-reef 

 corals and the c<jrals that grow in the lagoons. ^ This subject has 

 been discussed at great length by subsequent investigators, of whom 

 I am one, but althougti facts have been presented in a more or less 

 statistical way, the principle of adaptation of growth form to envi- 

 ronment was as clearly perceived by Darwin as it is by anyone to- 

 day. Dana's conclusions on the relations of corals to the tempera- 

 ture of the ocean have been modified in only a subordinate way. It 

 is scarcely known who first recognized the polymorphism of species 

 of corals according to difference in habit. The recognition of such 

 vegetative adaptation was at least foreshadowed by Khmzinger and 

 Pourtales. Brook clearly recognized the principle, and during more 

 recent years it has been elaborately discussed by Gardiner, Von 

 Marenzeller, Wood Jones, and many others, including myself. The 

 literature on coral ecology is enormous, and probably the ecologic 

 relations of no other group of marine organisms are so well known. 



Recently I have published two summaries on the physical condi- 

 tions under which coral reefs form,' and have discussed in detail the 

 temperature relations of coral reefs in a paper entitled Temperature 

 of the Florida Coral-reef Tract.^ Dr. A. G. Mayer has given im- 

 portant information on some of the subjects of coral ecology in a 

 paper entitled Ecology of the Murray Island coral reef;* and I 

 have given considerable data on the relation between the growth- 

 form of colonies and habitat in my monograph. Some shoal-water 

 corals from Murray Island (Australia), Cocos-Keeling Islands, and 

 Fanning Islands.'^ The last-mentioned paper contains a complete 

 bibliography of my publications on corals and coral reefs up to 

 March, 1917. 



In the second of my papers referred to m the preceding paragraph,^ 

 I state on page 99 : ' 



The conditions necessary for vigorous coral-reef development may be summarized 

 as follows: (1) Depth of water, maximum, about 45 meters; (2) bottom firm or rocky, 

 without silty deposits; (3) water circulating, at times strongly agitated; (4) an abun- 

 dant supply of small animal plankton; (5) strong light; (6) temperature, annual mini- 

 mum not below 18° C; (7) salinity between about 27 and 38 parts per thousand. 



To this should be added the statement that the mean temperature 

 of the coldest month must not be lower than about 21° C. 



1 structure and distribution of coral reefs, ed. 3, pp. 1-19, 1889. 



2 Vaughan, T. W., Physical conditions under wiiich Paleozoic coral reefs were formed, Geol. Soc. Amer 

 Bull., vol. 22, pp. 23&-252, 1911 ; The results of investigations of the ecology of the Floridian and Bahaman 

 shoal-water corals, Nat. Acad. Sci. Proc, vol. 2, pp. 95-100, 1916. See also Corals and the formation of 

 coral reefs, Smithsonian Ann. Kept, for 1917 (in press). 



3 Carnegie Inst. Washington Pub. 213, pp. 321-339, 1918. 

 * Idem, pp. 1-48, pis. 1-19, 1918. 



6 Idem, pp. 49-233, pis. 20-93, 1918. 



