HEAT TOLERANCE AND TEMPERATURE RELATIONSHIPS OF THE FIDDLER CRAB, UCA PUGILATOR, WITH REFERENCE TO BODY COLORATION

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Abstract
The objectives of this investigation were to determine the effect of humidity on body temperature and survival at high temperatures, the influence of body coloration on body temperature, and the rates of transporation at high temperatures. In saturated and dry air the lethal temperatures for 50% of the crabs after an exposure of 1 hour were 40.7[degree]C and 45.1[degree]C respectively. Five minutes after having been placed in sunlight the body temperature of dark crabs was 2[degree]C higher than that of pale crabs. More visible light is reflected from the dorsal surface of the cephalothorax of a pale crab than from a dark crab. The difference is more striking with the rays of longer wave length which have a greater heating capacity than the rays at the violet end of the visible spectrum. These observations support the hypothesis that the blanching that occurs at high temperatures has a thermoregulatory role. The rate of transpiration from this crab is proportional to the saturation deficit of the air. In their habitat the crabs exhibit a "feeding-retreat" rhythm that has a frequency of 18-24 minutes. There is no phase interaction between individuals. On hot days the frequent periodic return to the cooler burrows can serve to lower the body temperature.

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