ECOLOGY OF THE MURRAY ISLAND CORAL REEF. 



33 



The extreme range observed in air temperature 200 feet seaward from 

 the shore between September 30-October 23, 1913, was 2.8° C, while the 

 extreme range of water temperature for the same times and place was 12.5° C. 

 Early in the morning the water near shore was 0.9° to 3.0° cooler than the 

 air, whereas in the hottest part of the afternoon it was 4.2° to 6.7° warmer 

 than the air. Thus, over this reef-flat solar radiation, not air temperature, is 

 the chief factor in warming the water during the day, and during the night 

 the chief factor in cooling the water is radiation from the surface of the water 

 into outer space, not convection of heat by the cooling air. 



The results of these temperature observations are shown in graphic 

 form in figure 9. 



350 



50 



^ Highest water temperature 



j_t;2i:t__a"- ^ temperature 



Lowest 



Range in water t 



^O. 



Ran^e "m a 



200 



600 800 1.000 1.200 



DISTANCE IN FEET FROM SHORE 



— O — 



i.eoo 



Fig. 9. — Showing the temperatures and the range in temperature of the water and of the air over the 

 water along Line No. I on the southeast reef of Maer Island. 



It appears that while the surface of the sea outside the reef ranges 

 through 3.5°, the range over the reef-flat is greater than this and increases as 

 one approaches the shore, becoming 12.5° near the beach. Moreover, in 

 the hot calms of the northwest season in January, the temperatures over the 

 reef-flat must be considerably hotter than those observed during the cool 

 days of October, and it seems probable that the heat alone would be suffi- 

 cient to kill all corals within 450 feet of the shore, for, according to Mr. 



