172 CARNEGIE INSTITUTION OF WASHINGTON. 



The Director made an intensive oecological and physiological study 

 of the coral reefs at ^Vlaer Island, finding that temperature is the chief 

 factor which determines the habitats of the various species upon the 

 reef-flat. Moreover, in general it appears that in proportion as a coral 

 is able to withstand high temperature, it can usually in like ratio sur- 

 vive being buried under the mud. This suggests that high temperature 

 may produce death in corals by causing asphyxiation in the manner 

 stated by Winterstein in the case of frogs. Some corals, however, such 

 as Favia fragum and Mceandra areolata, die at relatively low tempera- 

 tures, but are highly resistant to the smothering effects of CO2 or of 

 being buried under the sand; yet they are nearly as resistant to heat 

 when buried as they are when living in the free open water, while those 

 corals that die at moderate temperatures are much more sensitive to 

 temperature when buried than when not buried. It seems, therefore, 

 that certain corals can, so to speak, go into a state resembling hiberna- 

 tion and still survive at a much lower metabolism than the normal, 

 whereas other corals, such as Acropora and Orbicella, can not adjust 

 themselves in this manner, but die if their metabolism be appreciably 

 lowered. Possibly similar relations may pertain to other hibernating 

 animals and may in a measure account for the observations of Amerling 

 and of Babak, that certain frogs and toads which died at a moderate 

 temperature could survive well in deficiency of oxygen, while others 

 which died at a high temperature were easily asphyxiated. In other 

 words, the vital limits of some animals may be adjustable, some to 

 higher and some to lower rates of metabolism than the normal, whereas 

 others may be confined to a relatively narrow temperature range. 



But to return to the corals: It was found that the physiological 

 reactions of the Pacific corals are similar to those of related Atlantic 

 genera, and that natural selection has not enabled the Florida corals to 

 increase their resistance to the cold of winter, or the Torres Straits 

 forms to better withstand the deadly heat of their hot season. There 

 is clear evidence of a struggle for existence among the various species of 

 the Murray Island reef-flat, but none whatsoever that any of these 

 species has thereby been improved by a selective process. 



It was found that the range in temperature of the water over shallow 

 reef-flats is considerably greater than that of the air above them, thus 

 showing that solar radiation, not conduction from the air, is the chief 

 source of heat for the ocean water. 



There is clear evidence of solution of limestone over the reef-flats 

 everywhere in Torres Strait, but we are not yet prepared to assert that 

 the sea-water as such causes this solution, for there are many other 

 factors, such as rain-water draining from the land, decomposition of 

 organic matter, acid-producing algse, worms, sponges, and mollusks, 

 and the digestive effects produced by echinoderms upon sand in their 

 alimentary tracts. One should consult Dr. Tashiro's report, published 



