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 (W) of seawater at 25∞C.Calcification rate of a massive coral Porites lutea cultured in a beaker showed a linear increase with increasing W aragonite values (1.08-7.77) of seawater.The increasing trend of calcification rate (c) for W is expressed as an equation, c = aW + b (a, b: constants).When W was larger than ~4, the coral samples calcified during nighttime, indicating an evidence of dark calcification.This study strongly suggests that calcification of Porites lutea depends on W 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.