Thermal effects of tissue optics in symbiont-bearing reef-building corals

Isabel M. Jimenez, Anthony W. D. Larkum, Peter J. Ralph and Michael Kühl

Limnol. Oceanogr., 57(6), 2012, 1816-1825 | DOI: 10.4319/lo.2012.57.6.1816

ABSTRACT: Reflectance spectroscopy and microscale temperature measurements were used to investigate links between optical and thermal properties of corals. Coral tissue heating showed a species-specific linear correlation to the absorptance of incident irradiance. Heat budgets estimated from absorptance and thermal boundary layer measurements indicated differences in the relative contribution of convection and conduction to heat loss in Porites lobata and Stylophora pistillata, and a higher heat conduction into the skeleton of the thin-tissued branching S. pistillata as compared to the massive thick-tissued P. lobata. Decreasing absorptance associated with bleaching resulted in decreased surface warming of coral tissue. Action spectra of coral tissue heating showed elevated efficiency of heating at wavelengths corresponding to absorption maxima of major zooxanthellae photopigments. Generally, energy-rich radiation (< 500 nm) showed the highest heating efficiency. Species-specific relationships between coral tissue heating and absorptance can be strongly affected by differences in the thermal properties of the skeleton and/or tissue arrangement within the skeletal matrix, indicating a yet unresolved potential for coral shape, size, and tissue thickness to affect heat dissipation and especially the conduction of heat into the coral skeleton.

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