20 Papers from the Marine Biological Laboratory at Tortugas. 



placed in large glass aquaria and the temperature was raised slowly at the 

 rate of about 2° C. per hour, with frequent stirring of the water. Time is 

 an important factor in these experiments, for animals can withstand a 

 higher degree of heat if the temperature be raised quickly than if it be raised 

 slowly. These experiments were made during May-July 1912, at Golding 

 Cay, Andros Island, Bahamas, and at Tortugas, Florida, when the normal 

 temperature of the sea-water ranged from 27° to 29.5° C. as shown in table 6. 



It appears that the reef corals at Tortugas, Florida, live in water which 

 is commonly within 10° C. of their upper death-temperature, and if the ocean 

 were heated to 38° C. (100.4° F.) only one species, Siderastrcea radians, could 

 survive. This form lives on the shallow flats, often in places where the 

 circulation is imperfect and where wide temperature ranges occur. Ac- 

 cordingly, it is also the species most resistant to cold, withstanding 6° to 

 7° C. without apparent injury, but usually being killed at about 4.5° C. 

 (40° F.), although one individual survived without apparent injury after 

 being at a temperature of 1.9° C. (35.4° F.) for 11 hours. 



Next to Siderastrcea radians the most resistant coral is S. siderea, although 

 it lives in relatively deep water on the outer reefs, where the circulation is 

 of the best and the temperature range is therefore slight. It is associated 

 in its habitat with Orbicella annularis, one of the most sensitive of the reef 

 corals, which is killed at 14.1" and 36.8° C. 



In general, however, the corals of the shallow-reef fiats, such as Sider- 

 astrcea radians, Porites furcata, and Mceandra areolata, are the most resistant 

 both to heat and cold, while those of deep water, such as Madrepora palmata, 

 Eiismilia knorri, and Oculina diffusa, are the least resistant. 



Forms such as Porites clavaria, P. astrcBoides, Mceandra muricata, Orbi- 

 cella annularis, O. cavernosa, and Favia fragum, which usually live in fairly 

 shallow but freely circulating water, all show moderate powers of resistance. 



The air-temperature at Tortugas commonly ranges from a maximum of 

 98° F. in summer to about 60° F. in winter,^ and the coldest "northers" in 

 winter appear to reduce the temperature of the water over the reefs to about 

 17.2° C. (63° F.). In view of this fact, the more abundant reef species 

 were maintained at about 13.9° C. (57° F.) for periods of at least 9 hours. 



As a result, we are led to conclude that were the water cooled by an 

 exceptionally prolonged norther to 13.9° C. for 9 hours, Siderastrcea radians, 

 S. siderea, and Mceandra areolata would survive without apparent injury, 

 while Porites furcata, P. clavaria, Mceandra clivosa, and Favia fragum would 

 also survive, but with more or less injury, the first-named being the most 

 resistant. On the other hand, this temperature would be fatal to Orbicella 

 annularis, Porites astrceoides, and Madrepora muricata (cervicornis) . 



The observations cited above are upon the death-temperatures, but the 

 temperatures at which the feeding reactions and normal metabolic processes 

 cease are much more significant, for naturally an animal can not long survive 



1 In the year from June i, 1912, to May 31. I9i3. the air temperature at Tortugas ranged from 95° to 

 65.5° F. as determined by a self-recording thermometer. 



