THE PHYSIOLOGY OF SKELETON FORMATION IN CORALS. I. A METHOD FOR MEASURING THE RATE OF CALCIUM DEPOSITION BY CORALS UNDER DIFFERENT CONDITIONS

Abstract

1. A method is described for the accurate measurement of calcification rates in reef-building corals under various controlled conditions, using calcium-45 as tracer.2. At the temperatures of the experiments, there was a slow but appreciable isotopic exchange between the coral skeleton and sea water. There are indications that this is considerably less in living coral where the tissue forms a barrier against such exchange.3. In many of the reef-building corals tested so far, the calcification rate was significantly lowered by the exclusion of light.4. The calcification rate of reef corals grown in darkness for prolonged periods of time to remove the zooxanthellae is considerably reduced and seems independent of the light intensity.5. Variations in the growth rates of different parts of coral colonies were measured. The existence of growth gradients was demonstrated in a number of species.6. Calcium uptake was greatly reduced on the addition of Diamox, a specific carbonic anhydrase inhibitor. In those species tested, the effect of carbonic anhydrase inhibition and exclusion of light was in the same direction. In the presence of complete inhibition of carbonic anhydrase there was still an uptake, even in darkness.7. It was concluded that the effect of light on reef coral growth is in part mediated through the zooxanthellae. The decreased calcification rates of reef corals in darkness, in the absence of zooxanthellae or in the presence of a carbonic anhydrase inhibitor suggest that the rapid calcification of these corals may be dependent on efficient removal of H2CO3.