Skeletal mechanical properties of Mediterranean corals along a wide latitudinal gradient

Abstract

This is the first study exploring skeletal mechanical properties in temperate corals. The variation of skeletal mechanical properties with distance from the aboral pole, coral age, and population was investigated in the corals Balanophyllia europaea (zooxanthellate) and Leptopsammia pruvoti (non-zooxanthellate), collected at three sites along a wide latitudinal gradient. Mechanical properties were measured by nanoindentation, a technique applied here in detail for the first time to a scleractinian. In both species, a reduction of Young’s modulus was observed toward the oral pole, which is the youngest part of the skeleton. Skeletons of B. europaea increased their Young’s modulus with age, unlike L. pruvoti. Only the zooxanthellate species showed reduced Young’s modulus in southern populations, coherently with the observed reduced skeletal bulk density and porosity with SST (decreasing latitude) in B. europaea, and with the lack of correlations with SST and latitude for skeletal bulk density and porosity in L. pruvoti. These results support previous hypotheses on differences in the skeletal mechanical properties of these two coral species in relation to the observed variations of skeletal bulk density and porosity with temperature/latitude, which may have consequences related to the envisaged seawater warming of next decades.