Incorporation of metabolic CO2 into coral skeleton

Abstract

Two possible sources for the carbonate in the calcium carbonate coral skeleton are (a) soluble carbonates from seawater and (b) carbon dioxide produced in metabolism by the living coral tissue. Although radioisotopic tracer experiments have established that carbonate from sea-water is incorporated into the skeleton by many corals1-3, evidence for incorporation of metabolic CO2 into the skeleton is much less direct. Goreau 1 found that calcification rates measured by incorporation of radioactive carbonate from seawater were usually lower than those measured by using radioactive calcium; he proposed that the labelled carbonate might be diluted by unlabelled carbonate in coral tissue. In addition, findings that the ratios of 13C to 12C and of 18O to 16O in seawater differ from those in coral skeleton suggest that not all of the skeletal carbonate originates directly from carbonate in seawater4-7. To examine further the possibility that some skeletal carbonate originates from metabolic CO2, I fed 14C- labelled mouse tissue to small individuals of the coral Fungia scutaria, a solitary polyp containing symbiotic algae. © 1970 Nature Publishing Group.