Effects of calcium ion concentration on calcification rates of six stony corals: A mesocosm study

Abstract A 1.5-ton indoor artificial coral reef mesocosm was established in order to evaluate the effects of changes in calcium ion (Ca 2+ ) concentration on calcification of six stony corals, including two species of Acroporiidae ( Acropora millepora and A. echinata ), three species of Pocilloporidae ( Pocillopora damicorins , Stylophora pistillata and Seriatopora caliendrum ) and one species of Agariciidae ( Pavona decussata ). Periodic addition of CaCl 2 was conducted to obtain a long-term series (23 weeks) of six reef coral calcification rates. Species-specific calcification rates were found among six stony corals, which shows linear increase in S. pistillata and A. millepora and exponential increase in S. caliendrum with elevated ambient seawater Ca 2+ concentrations (ranging from 157.4 mg/L to 456.7 mg/L). Calcification rates tended to plateau with increased ambient seawater Ca 2+ concentration (300–400 mg/L) for P. damicornis , while displaying a reverse parabolic pattern for A. echinata and P. decussata . We hypothesized that Ca 2+ deposition by most stony corals would follow Michaelis-Menten kinetics, but the plateau would be reached at different Ca 2+ concentrations for different coral species. Linear or exponential increases with Ca 2+ concentrations observed in S. pistillata , A. millepora and S. caliendrum may be still at the initial stages of Michaelis-Menten curve, and they did not reach peak calcification rates at 2+ concentration. This work is valuable in providing instruction for the methodology and timing for periodical Ca 2+ supplementation in closed recirculating aquacultural systems for stony corals.