TISSUE RETRACTION IN THE SCLERACTINIAN CORAL COELOSERIS-MAYERI, ITS EFFECT UPON CORAL PIGMENTATION, AND PRELIMINARY IMPLICATIONS FOR HEAT-BALANCE

Extreme tissue retraction in the agariciid coral Coeloseris mayeri occurs during periods of sub-aerial exposure. The retraction response appears to involve independent movement of oral and aboral tissue layers to such an extent that skeletal septa are uncovered. Tissue retraction results in a significant paling in colony colour which does not involve any reduction in either zooxanthellae abundance or chlorophyll concentration. Adaptive benefits of the response include increased albedo, leading to a reduction in absorbed solar energy of 10 % for wavelengths between 280 and 700 nm, and possible avoidance of photochemical damage or photoinhibition at high solar irradiance. The degree of retraction is governed by environmental conditions, including length of sub-aerial exposure, and intensity of solar irradiance.