Ahermatypic corals, and hermatypic corals without zooxanthellae, have Sr and U concentrations that are greater than those of reef corals containing zooxanthellae. The Sr and U concentrations in the corals are independent of water temperature, in that respect differing from those in aragonite experimentally precipitated from sea-water in the laboratory. The deposition of Sr and U in scleractinian coral aragonite may be related to coral metabolic processes and to the influence of algal photosynthesis on calcification rates.