Effect of CaCO3 (aragonite) saturation state of seawater on calcification of Porites coral

Using living corals collected from Okinawan coral reefs, laboratory experiments were performed to investigate the relationship between coral calcification and aragonite saturation state (Omega) of seawater at 25 degreesC. Calcification rate of a massive coral Porites lutea cultured in a beaker showed a linear increase with increasing Omega(aragonit) values (1.08-7.77) of seawater. The increasing trend of calcification rate (c) for Omega is expressed as an equation, c = aOmega + b (a, b: constants). When Omega was larger than similar to4, the coral samples calcified during nighttime, indicating an evidence of dark calcification. This study strongly suggests that calcification of Porites lutea depends on Omega of ambient seawater. A decrease in saturation state of seawater due to increased pCO(2) may decrease reef-building capacity of corals through reducing calcification rate of corals.