Response to: Coral reef calcification - carbonate, bicarbonate and proton flux under conditions of increasing ocean acidification

We respond to the comment 'Coral reef calcification: carbonate, bicarbonate and proton flux under conditions of increasing ocean acidification' by Jokiel, who uses our data to test his 'proton flux hypothesis', which accounts for the negative effect of ocean acidification (OA) on the calcification of reef corals. We applaud the use of our empirical data to explore hypotheses differing from our own to draw attention to possible associations between pairs of dependent variables that can provide insight into cause-and-effect relationship resulting in coral calcification being depressed by high pCO2 in seawater. As described recently, robust data are necessary to project the impact of OA on coral reefs into the future and test hypotheses regarding the underlying mechanisms by which OA depresses calcification by coral reef calcifiers. The use of absolute units (e.g. mg CaCO3 d?1 cm?2) is critical when measuring calcification in perturbation experiments in order to retain the greatest capacity for subsequent synthesis and reinterpretation, as has been accomplished by Jokiel using our data. We note that this would not have been possible with calcification expressed in relative units (i.e. %), as is often the case.