Journal
JOURNAL OF THE ROYAL SOCIETY INTERFACE
Volume 11, Issue 93, Pages -Publisher
ROYAL SOC
DOI: 10.1098/rsif.2013.0997
Keywords
light energy budget; microsensors; light utilization; thermal boundary layer; photosynthetic efficiency; bio-optics
Categories
Funding
- Knud Hojgaards Fond
- Oticon Fonden
- Thorsons Rejselegat
- Kobenhavn Universitets Faelleslegat
- Danish Council for Independent Research \ Natural Sciences
- Australian Research Council
- University of Technology, Sydney
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The light field on coral reefs varies in intensity and spectral composition, and is the key regulating factor for phototrophic reef organisms, for example scleractinian corals harbouring microalgal symbionts. However, the actual efficiency of light utilization in corals and the mechanisms affecting the radiative energy budget of corals are underexplored. We present the first balanced light energy budget for a symbiont-bearing coral based on a fine-scale study of the microenvironmental photobiology of the massive coral Montastrea curta. The majority (more than 96%) of the absorbed light energy was dissipated as heat, whereas the proportion of the absorbed light energy used in photosynthesiswas approximately 4.0% under an irradiance of 640 mu mol photons m(-2) s(-1). With increasing irradiance, the proportion of heat dissipation increased at the expense of photosynthesis. Despite such low energy efficiency, we found a high photosynthetic efficiency of the microalgal symbionts showing high gross photosynthesis rates and quantum efficiencies (QEs) of approximately 0.1 O-2 photon(-1) approaching theoretical limits under moderate irradiance levels. Corals thus appear as highly efficient light collectors with optical properties enabling light distribution over the corallite/tissue microstructural canopy that enables a high photosynthetic QE of their photosynthetic microalgae in hospite.
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