196 



ANNUAL REPOKT SMITHSONIAN INSTITUTION, 1917. 



Table showing distance from shore, depth of water, character of bottom, num- 

 ber of species, and growth form of the colonies, for each station on line I, 

 southeast reef, Murray Island. 



Distance from shore 

 (in feet) 



300. 



400 



450-550 



600-650 



800-820 



1,000-1,020. 

 1,200-1,250. 

 1,400-1,445. 

 1,600-1,675. 

 1,720-1,775. 



Depth 



of water 

 at low 

 tide (in 

 inches). 



Character of bottom. 



4.5-5 

 6 -12 

 6.5-10 

 10 -11 

 14 -17 

 12 -16 

 14 -15 

 10 -16 

 2.5-3 



Hard limestone mud over lava 



rock. 



Firm limestone mud 



Sand and mud, rock 



Sandy 



Broken coral 



Rocky 



Rocky 



Rocky, broken coral 



Hani, rocky, broken coral. 



Ilard, rocky, with crevice like 



tide pools. 



Num- 

 ber of 

 species 

 at each 

 station. 



7 

 10 

 18 

 > 20 

 21 

 18 

 24 

 32 

 13 



Number of species accord- 

 ing to growth form. 



Fragile 



branches 



and free 



disks. 



' Stout 

 branches, 



incrust- 

 ing. 



1 Acropora pectinala (Hrook), v '• ich is of discoid corymbose growth form, is not counted in the tabulation. 



Comparison of this with the preceding table reveals precisely the 

 same principles. 



The collection made by Doctor Mayer at Murray Island contains 

 an excellent illustration of the variation of Stylo pTwra pistillata 

 (Esper) according to environment. The branches of a specimen 

 from a depth of 18 fathoms, northwest of Murray Island, where the 

 water is not violently agitated, are slender, elongate, and fragile 

 (pi. 7, fig. 1), while a specimen from the exposed reef has very short, 

 stumpy branches (pi. 7, fig. 2). Plate 8, figure 2, illustrates Porltes 

 porltcs from the exposed reef at Tortugas, Florida, while plate 8, 

 figure 1, illustrates the growth form assumed by a fragment broken 

 from the exposed reef and then attached to a terra-cotta disk and 

 planted within Tortugas lagoon. 



In shallow water, corals which have fragile skeletons or which are 

 weakly attached to the bottom predominate in lagoons, where the 

 water is not violently disturbed; and usually conditions favorable 

 for the life of corals having these kinds of growth habits are present 

 outside lagoons in depths between 18 and 25 fathoms. But on the 

 exposed sea-sides of reefs, where the surf is strong and storm waves 

 break, all the corals have strong skeletons, mostly of massive growth 

 form. If the same species of branching coral occurs both in places 

 protected from the beat of the surf and in those exposed to the 

 breakers, the colonies in the exposed situations adjust themselves to 

 their environment by strengthening theix skeletons. The preceding 

 paragraphs show that these adjustments take place in the Cocos- 

 Keeling Islands, on the Great Barrier of Australia, and in Florida, 

 and warrant the conclusion that the phenomena are of general occur- 



