Bicarbonate addition promotes coral growth

The addition of 2 mM bicarbonate to aquaria containing tropical ocean water and branches of Porites porites caused a doubling of the skeletal growth r ate of the coral. Nitrate or ammonium addition (20 mu M) to oligotrophic se awater caused a significant reduction in coral growth, but when seawater co ntaining the extra bicarbonate was supplemented with combined nitrogen, no depression of the higher growth rate was evident. We infer that (1) the pre sent dissolved inorganic carbon (DIC) content of the ocean limits coral gro wth, (2) this limitation is exacerbated by nitrate and ammonium, and (3) ad ding DIC increases coral calcification rates and confers protection against nutrient enrichment.