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Front. Mar. Sci. | doi: 10.3389/fmars.2018.00068

ATP supply may contribute to light-enhanced calcification in corals more than abiotic mechanisms

  • 1Dept. of Oceanography, National Institute of Oceanography and Experimental Geophysics, Italy
  • 2International Centre for Theoretical Physics, Italy

Zooxanthellate corals are known to increase calcification rates when exposed to light, a phenomenon called light-enhanced calcification that is believed to be mediated by symbionts’ photosynthetic activity. There is controversy over the mechanism behind this phenomenon, with hypotheses coarsely divided between abiotic and biologically-mediated mechanisms. At the same time, accumulating evidence shows that calcification in corals relies on active ion transport to deliver the skeleton building blocks into the calcifying medium, making it is an energetically costly activity.
Here we build on generally accepted conceptual models of the coral calcification machinery and conceptual models of the energetics of coral-zooxanthellae symbiosis to develop a model that can be used to isolate the biologically-mediated and abiotic effects of photosynthesis, respiration, temperature, and seawater chemistry on coral calcification rates and related metabolic costs.
We tested this model on data from the Mediterranean scleractinian Cladocora caespitosa, an acidification resistant species. We concluded that most of the variation in calcification rates due to photosynthesis, respiration and temperature can be attributed to biologically-mediated mechanisms, in particular to the ATP supplied to the active ion transports. Abiotic effects are also present but are of smaller magnitude. Instead, the decrease in calcification rates caused by acidification, albeit small, is sustained by both abiotic and biologically-mediated mechanisms. However, there is a substantial extra cost of calcification under acidified conditions.
Based on these findings and on a literature review we suggest that the energy aspect of coral calcification might have been so far underappreciated.

Keywords: corals, calcification, Light Enhanced Calcification, biological control, Calcification Cost, Calcification model, temperature, acidification

Received: 27 Oct 2017; Accepted: 14 Feb 2018.

Edited by:

Sönke Hohn, Leibniz Centre for Tropical Marine Research (LG), Germany

Reviewed by:

Anthony W. Larkum, University of Technology Sydney, Australia
Virginie Raybaud, University of Nice Sophia Antipolis, France  

Copyright: © 2018 Galli and Solidoro. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Dr. Giovanni Galli, GALLI., National Institute of Oceanography and Experimental Geophysics, Dept. of Oceanography, via Beirut 2, Trieste, 34151, Italy, Italy, ggalli@inogs.it