ECOLOGY OF THE MURRAY ISLAND CORAL REEF. 



35 



The author also made some experiments upon the corals of Porto Rico 

 and of Tortugas (Florida) and found that upon gradually cooling the sea- 

 water within which hungry reef corals are living they gradually lost their 

 activity and with it their ability to capture food (crab or snail meat). Food 

 already captured, however, could be held upon the surface of the tentacles 

 or other parts to within i° C. of the death temperature, whereas the corals 

 lost the power to seize fresh pieces of crab meat at about 3° to 5° C. above 

 the death temperature for cold. 



Table 7. 



Table 8. 



Table 8 shows the extremes for a number of determinations upon dif- 

 ferent individual coral stocks, each coral being held for i hour at the tem- 

 perature stated. Thus, after one hour at about 6i° F., or i6° C, most of 

 the reef corals would be unable to capture food, and doubtless a sustained 

 exposure to 18.5° C. would be fatal if from 

 no other cause than that it would result in 

 starving the corals. 



It would seem that Australian corals, 

 which are never called upon in nature to 

 withstand the effects of cold, are about as 

 able to resist low temperatures as are the 

 corresponding genera of Florida.^ This is 

 interesting, for nearly every winter the 

 Florida corals are brought close to their death temperature by the cold 

 northerly storms, and yet natural selection has not enabled them to attain 

 an increased resistance to cold. Similarly, the Australian corals, which are 

 annually called upon to withstand a higher temperature than are those of 

 Florida, are not more resistant in this respect than are Florida corals. The 

 whole matter of temperature resistance is physiological and natural selection 

 appears to have had nothing to do with improving it. 



'See Mayer, A. G., 1914, Carnegie Wash., Researches from the Tortugas Laboratory, vol. vi, p. 19. 



