In his comment on our paper, Moran (Moran, 2014) raises the important issue of ensuring that experiments investigating the responses of marine organisms to future ocean acidification scenarios are carried out with a high degree of certainty about the CO2 levels being tested. We agree wholeheartedly, which is why we take considerable care in measuring and validating pCO2 in our field-based and laboratory experiments. Here we explain, more fully than was possible in a Short Communication, the procedures used to measure and cross-validate pCO2 in Chung et al. (Chung et al., 2014) and other studies we have conducted over recent years (in which the methods have been reported). These techniques are in accordance with those mentioned by Moran and detailed descriptions are already available in the literature (e.g. Hari et al., 2008). We also correct a number of factual errors and incorrect assumptions made by Moran in his comment.
Moran states that because of the ‘dependence of the Chung et al. study on pH to determine test pCO2 levels, the dose–response effect reported in the paper should be treated with caution’ and that ‘we cannot assert that the target CO2 levels were correct’. The author proposes that: ‘Ideally, direct pCO2 measurements should be made via nondispersive infrared measurement (NDIR), where the dissolved gases are equilibrated with a carrier gas which passesthrough an infrared analyser.’ Indeed, that is exactly what was done in our experiment. (…)
Munday P. L., Watson S.-A., Chung W.-S., Marshall N. J. & Nilsson G. A., 2014. Response to ‘The importance of accurate CO2 dosing and measurement in ocean acidification studies’. Journal of Experimental Biology 217:1827-1829. Article (subscription required).
