Effects of Temperature on Tropical Marine Animals. 



19 



At Tortugas, on the other hand, a very slight departure in temperature either 

 above or below 29° C. causes a decided falling-off in rate. 



The contrast between the behavior of Aurellia at Tortugas and at 

 Halifax is shown in figure 8 wherein the ordinates represent average rates of 

 pulsation and the abscissae temperatures, the curve ABC applying to the 

 medusae from Halifax, while FDE shows the general reactions of the same 

 species from the warm waters of Tortugas, Florida. 



The wide range in temperature in which these northern forms are about 



normal or only slightly increasing in activity accords with the fact that 



tropical marine animals are, physiologically speaking, but poorly adjusted 



to their temperature environment in comparison with creatures of colder 



waters, for the tropical forms live near their upper death-points and slight 



elevation in temperature affects them adversely. Nor are they capable of 



withstanding the same proportionate degree of cold as do northern forms, 



as may be seen after every severe "norther" in winter, when the Florida 



beaches are strewn with reef fishes which have succumbed to the cold^ 



although the temperature of the water over the reefs in these storms rarely 



declines below 17° C. 



Table 6. 



' Survives without apparent injury after being for 9 



hours at 11.2° to 12.1° C. 

 "Survives 13° to i4-4° C.for 9 hours; half killed by 



11.2° to 12.1° for 9 hours. 

 ' Apparently uninjured by 13.2-15.1° for 10.5 hours. 

 * Killed by 13° to 14.4° for 9 hours. 



"i Nearly killed by 13.2° to 15.1° for 10.5 hours. 



« Not injured by 13.85° to 16.8° for 9 hours. 



' Killed by 14° to 15° for 9 hours. 



8 Injured but survived 13.85° to 16.8° for 9 hours. 



' Killed by 14° to 15.8° for 9 hours. 



■"Killed by 13.3° to 15° C. for 9 hours. 



The reef corals are interesting, for, as is well known, they are restricted 

 to tropical seas. Accordingly, the vital limits in respect to temperature 

 of the 18 most abundant reef species of the Florida-Bahama region were 

 studied.^ The results are presented in table 6, the method pursued being 

 the same as in all other experiments recorded in this paper : the corals were 



' Experiments upon corals of the Great Barrier Reef of Australia, near Torres Straits, show that their 

 temperature reactions are on the whole similar to those of the corresponding Atlantic genera. Thus natural 

 selection has not aided the Florida corals in withstanding cold, or improved the resisting powers of the Pacific 

 forms in respect to heat. 



