Interactive effects of ocean acidification and temperature on two scleractinian corals from Moorea, French Polynesia

This study tested the hypothesis that the response of corals to temperature andpCO2is consistent between taxa. Juvenile massivePoritesspp. and branches ofP. rusfrom the back reef of Moorea were incubated for 1 month under combinations of temperature (29.3 °C and 25.6 °C) andpCO2(41.6 Pa and 81.5 Pa) at an irradiance of 599 μmol quanta m−2s−1. Using microcosms and CO2gas mixing technology, treatments were created in a partly nested design (tanks) with two between‐plot factors (temperature andpCO2), and one within‐plot factor (taxon); calcification was used as a dependent variable.pCO2and temperature independently affected calcification, but the response differed between taxa. MassivePoritesspp. was largely unaffected by the treatments, butP. rusgrew 50% faster at 29.3 °C compared with 25.6 °C, and 28% slower at 81.5 Pa vs. 41.6 Pa CO2. A compilation of studies placed the present results in a broader context and tested the hypothesis that calcification for individual coral genera is independent ofpH, [HCO3−], and [CO32−]. Unlike recent reviews, this analysis was restricted to studies reporting calcification in units that could be converted to nmol CaCO3 cm−2 h−1. The compilation revealed a high degree of variation in calcification as a function ofpH, [HCO3−], and [CO32−], and supported three conclusions: (1) studies of the effects of ocean acidification on corals need to pay closer attention to reducing variance in experimental outcomes to achieve stronger synthetic capacity, (2) coral genera respond in dissimilar ways topH, [HCO3−], and [CO32−], and (3) calcification of massivePoritesspp. is relatively resistant to short exposures of increasedpCO2, similar to that expected within 100 y.