By absorbing about a third of human-made carbon dioxide, the ocean decelerates global warming. However, when dissolved in seawater, carbon dioxide reacts to produce carbonic acid, causing seawater pH to decrease. It also diminishes the concentration of carbonate ions, thereby putting organisms forming their shells and skeletons from calcium carbonate at risk. Apart from plankton, algae, mussels and snails, stony corals are among those particularly endangered: Their skeletons consist of aragonite, the most soluble form of calcium carbonate....