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Biogeosciences An interactive open-access journal of the European Geosciences Union
https://doi.org/10.5194/bg-2017-58
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
01 Mar 2017
Review status
A revision of this discussion paper was accepted for the journal Biogeosciences (BG) and is expected to appear here in due course.
Daily variation in net primary production and net calcification in coral reef communities exposed to elevated pCO2
Steeve Comeau1,2, Peter J. Edmunds1, Coulson A. Lantz1,3, and Robert C. Carpenter1 1Department of Biology, California State University, 18111 Nordhoff Street, Northridge, CA 91330-8303, USA
2School of Earth Sciences, Oceans Institute and ARC Centre of Excellence for Coral Reef Studies, The University of Western Australia, Crawley, Western Australia 6009, Australia
3Southern Cross University School of Environment, Science, and Engineering, Military Road Lismore NSW 2480 Australia
Abstract. The threat represented by ocean acidification (OA) for coral reef has received considerable attention because of the sensitivity of calcifiers to changing water carbonate chemistry. However most studies have focused on the organismic response of calcification to OA, and only a few have addressed community-level effects, or investigated parameters other than calcification, such as photosynthesis. Light (Photosynthetically Active Radiation, PAR) is a driver of biological processes on coral reefs, and the possibility that these processes might be perturbed by OA has important implications for community function. Here we investigate how CO2 enrichment affects the relationships between PAR and community net O2 production (Pnet), and between PAR and community net calcification (Gnet), using experiments on three coral communities constructed to match (i) the back reef of Moorea, French Polynesia, (ii) the fore reef of Moorea, and (iii) the reef flat of Oahu, Hawaii. The results were used to test the hypothesis that OA affects the relationship between Pnet and Gnet. For the three communities tested, pCO2 did not affect the Pnet-PAR relationship, but it affected the intercept of the hyperbolic tangent curve fitting the Gnet-PAR relationship for both reef communities in Moorea (but not in Oahu). For the three communities, the slopes of the linear relationships between Pnet and Gnet were not affected by OA, although the intercepts were depressed by the inhibitory effect of high pCO2 on Gnet. Our result indicates that OA can modify the balance between net calcification and net photosynthesis of reef communities by depressing community calcification, but without affecting community photosynthesis.

Citation: Comeau, S., Edmunds, P. J., Lantz, C. A., and Carpenter, R. C.: Daily variation in net primary production and net calcification in coral reef communities exposed to elevated pCO2, Biogeosciences Discuss., https://doi.org/10.5194/bg-2017-58, in review, 2017.
Steeve Comeau et al.
Steeve Comeau et al.

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Short summary
Here we investigate how CO2 enrichment affects in coral reef communities the relationships light–production and light–calcification. For the three communities tested, CO2 did not affect the light–production, while calcification was lower at elevated CO2 for all light levels. Our result indicates that CO2 can modify the balance between net calcification and net photosynthesis of reef communities by depressing community calcification, but without affecting community photosynthesis.
Here we investigate how CO2 enrichment affects in coral reef communities the relationships...
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