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 occ urs during periods of sub-aerial exposure. The retraction response app ears 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 invol ve any reduction in either zooxanthellae abundance or chlorophyll conc entration. Adaptive benefits of the response include increased albedo, leading to a reduction in absorbed solar energy of 10 % for wavelengt hs between 280 and 700 nm, and possible avoidance of photochemical dam age or photoinhibition at high solar irradiance. The degree of retract ion is governed by environmental conditions, including length of sub-a erial exposure, and intensity of solar irradiance.