Coral reefs are particularly vulnerable to ocean acidification that results from increased anthropogenic carbon dioxide in the atmosphere. Among other effects, the lower pH reduces the availability of carbonate ions ( CO 3 2 ), used by corals to create the calcium carbonate skeletons that form the bulk of the reef structure. Reefs are complicated, diverse ecosystems. They contain other calcifying organisms, including some algae. What’s more, calcification rates are influenced by temperature, light, and other environmental factors. And acidification can increase the rate of calcium carbonate dissolution.

Rebecca Albright, Ken Caldeira, and colleagues now report on an in situ experiment that isolated the effect of ocean acidification on the net calcification of an entire coral-reef community. By bubbling CO2 into a tank of ambient seawater, the researchers artificially lowered the water’s pH. They then pumped the water over an unconfined, flat 400 m2 region...

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