Kinetics of strontium uptake in the scleractinian coral Stylophora pistillata

Reef-building corals are very sensitive to changes in their environment and have been identified as potential accurate recorders of environmental changes. They form aragonitic carbonate skeletons that contain relatively high amounts of strontium (Sr2+). The ratio of Sr2+/calcium (Ca2+) has been proved to be useful for paleoclimatic studies since it has been suggested to vary with the seawater temperature. However, no correlation can be established between skeletal Sr2+ content and environmental parameters due to the lack of knowledge concerning the extent to which skeletal chemistry is controlled by physiological parameters. In this study, we investigated the pathway of Sr2+ incorporation by the scleractinian coral Stylophora pistillata. For this purpose, we used Sr-85 and a non-destructive NaI gamma detector. Sr2+ skeletal incorporation was found to be linear during the 9 experimental days of incubation with natural concentrations of Sr2+. The incorporation of Sr2+ versus external Sr2+ concentration was also linear up to 3.42 mM (i.e. a concentration 37.5 times higher than normal seawater concentration). However, the uptake of Sr2+ at high concentrations (> 1 mM) decreased with an increase in Ca2+ concentration in the seawater. Moreover, Verapamil, a Ca2+ channel inhibitor, also inhibits the incorporation of Sr2+ with the same I-c50 (12 muM) as for Ca2+. Incorporation of Sr2+ is therefore inversely correlated to the rate of calcification, suggesting interactions between these 2 ions, which should be taken into account during paleoclimatic studies.