Coral calcification: Sources of error in radioisotope techniques

Isotopic exchange occurs between coral skeleton and ⁴⁵Ca⁺⁺ and H¹⁴CO ₃ ^- in seawater. Exchange of ¹⁴C onto skeletons is more rapid than exchange of ⁴⁵Ca⁺⁺. Exchange of ¹⁴C from skeletons to seawater takes place more slowly than exchange of ⁴⁵Ca⁺⁺ to seawater. When living coral is incubated in the dark with radioisotopes for 1 h, the tissues contain considerably more radioactivity than is associated with the skeleton. The tissue radioactivity reflects permeation of tissues and coelenteron by radioactive compounds from the incubation seawater. Addition of alkalis to cardioactive seawater results in a radioactive precipitate, part of which becomes associated with any coral skeleton present, and part of which forms on the wall of the containing vessel. Strong alkali removes biologically-deposited radioisotope from coral skeletons. Deposition, of ¹⁴C from H¹⁴CO ₃ ^- in skeletons of living coral incubated in the dark is greater than in dead coral. The reverse situation occurs with ⁴⁵Ca⁺⁺.