Anomalies in coral reef community metabolism and their potential importance in the reef CO(2) source-sink debate

It is not certain whether coral reefs are sources of or sinks for atmospheric CO(2). Air–sea exchange of CO(2) over reefs has been measured directly and inferred from changes in the seawater carbonate equilibrium. Such measurements have provided conflicting results. We provide community metabolic data that indicate that large changes in CO(2) concentration can occur in coral reef waters via biogeochemical processes not directly associated with photosynthesis, respiration, calcification, and CaCO(3) dissolution. These processes can significantly distort estimates of reef calcification and net productivity and obscure the contribution of coral reefs to global air–sea exchange of CO(2). They may, nonetheless, explain apparent anomalies in the metabolic performance of reefs close to land and reconcile the differing experimental findings that have given rise to the CO(2) debate.