Oxygen isotope ratios in the aragonite precipitated by the scleractinian reef-building corals indicate that the skeletal carbonate is not in isotopic equilibrium with the sea water of the reef environment in which the corals grew. Despite this apparent isotopic disequilibrium, δ18O values are temperature dependent. The δ18O versus temperature curves for various coral genera are parallel or nearly parallel to the isotopic ‘paleotemperature scale’ established by Epstein et al. (1953) but in each case the curves are displaced toward lower 18O/16O ratios at a given temperature. Regression coefficients for 44 genera have been determined. These findings suggest that if skeletal carbonate is derived from both sea-water bicarbonate and metabolic carbon dioxide, the relative proportions contributed by each of these two sources of carbon and oxygen are essentially constant for a given genus, but are different from one genus to another. Thus it is possible that isotopic composition can indicate relative excretory efficiency and that stable isotope ratios can be of considerable value in elucidating some of the processes involved in reef coral development.
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Weber et al. (1972) studied this question.