Interactive comment on “Ocean acidification increases photosynthate translocation in a coral–dinoflagellates symbiosis” by P. Tremblay et al.

This is not a full review, just an open comment providing some suggestions on this interesting manuscript.

– The title and first paragraph of the introduction set the experiments in the context of anthropogenic ocean acidification and the abstract concludes “this decrease might have important consequences for the survival of corals under an acidification stress”. Yet, the perturbation used, pH of 7.2 and pCO2 of almost 4000 atm, are not relevant in this context. Barry et al. (2011) provide guidelines on the experimentaldesign of ocean acidification perturbation experiments. I suggest that the title, abstract and introduction should be revised in order to avoid misleading the readership.

– It is absolutely essential to mention the pH scale used (pHNBS, pHT, pHf or pHSWS) every time a pH value is reported (see Pesant et al., 2010). Yet, the pH scale is not mentioned at all in this manuscript. The reader is referred to the discussion paper of Cohen and Fine (2012) which used the NBS scale andconverted the values on the total scale using a very approximate approach.

– Arbitrary values are used for the photosynthetic and respiratory quotients (respectively1.1 and 0.8). There are very few values reported in the literature for scleractinian corals but data are available for the species investigated here (Stylophora pistillata) from a very close location in the Gulf of Aqaba (Gattuso and Jaubert, 1990). These values range from 1 to 1.5 for PQnet and from 0.7 to 1 for RQc. I am not sure whether using these values would significantly alter the results and conclusions but the authors may want to address this concern.

I hope that the authors will find these comments useful.

Reference cited
Barry J. P., Tyrrell T., Hansson L. & Gattuso J.-P., 2010. CO2 targets for ocean acidification perturbation experiments. In: Riebesell U., Fabry V. J., Hansson L. & Gattuso J.-P. (Eds.), Guide to best practices for ocean acidification research and data reporting, pp. 53-66. Luxembourg: Publications Office of the European Union.

Cohen S. & Fine M., 2012. Measuring gross and net calcification of a reef coral under ocean acidification conditions: methodological considerations. Biogeosciences Discussions 9:8241-8272.
Gattuso J.-P. & Jaubert J., 1990. Effect of light on oxygen and carbon dioxide fluxes and on metabolic quotients measured in situ in a zooxanthellate coral. Limnology and Oceanography 35:1796-1804.

Pesant S., Hook L. A., Lowry R., Nisumaa A.-M. & Pfeil B., 2010. Safeguarding and sharing ocean acidification knowledge. In: Riebesell U., Fabry V. J., Hansson L. & Gattuso J.-P. (Eds.), Guide to best practices for ocean acidification research and data reporting, pp. 243-258. Luxembourg: Publications Office of the European Union.

Gattuso J.-P., 2013. Interactive comment on “Ocean acidification increases photosynthate translocation in a coral–dinoflagellates symbiosis” by P. Tremblay et al. Biogeosciences Discussions 10: C1-C3. Interactive comment.


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