A Time-Domain Nuclear Magnetic Resonance Study of Mediterranean Scleractinian Corals Reveals Skeletal-Porosity Sensitivity to Environmental Changes

Mediterranean corals are a natural model for studying global warming, as the Mediterranean basin is expected to be one of the most affected regions and the increase of temperature is one of the greatest threats for coral survival. We have analyzed for the first time with Time Domain Nuclear Magnetic Resonance (TD-NMR) porosity and pore-space structure, important aspects of coral skeletons, of two scleractinian corals, Balanophyllia europaea (zooxanthellate) and Leptopsammia pruvoti (non-zooxanthellate), taken from three different sites on the western Italian coast along a temperature gradient. Comparisons have been made with Mercury Intrusion Porosimetry and SEM images. TD-NMR parameters are sensitive to changes of the pore-structure of the two coral species. A parameter, related to the porosity, is larger for Leptopsammia pruvoti than for Balanophyllia europaea, confirming previous non-NMR results. Another parameter representing the fraction of the pore-volume with pore-sizes less than 10-20 um is inversely related, with high statistical significance, to the mass of the specimen, and, for Balanophyllia europaea, to the temperature of the growing site. This effect in the zooxanthellate species, that could reduce its resistance to mechanical stresses, may depend on an inhibition of the photosynthetic process at elevated temperatures and could have particular consequences in determining the effects of global warming on these species.