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Abstract

Corals construct skeletons by extracellular precipitation of calcium carbonate in the form of orthorhombic aragonite. These structures not only play a role in the global carbon budget, but also create complex three-dimensional habitat that has significant ecological and economic value. Environmental conditions affect physical properties of coral, including calcification rate, skeletal density, and porosity. Changes in these conditions can result in decreased skeletal stiffness, making corals more susceptible to physical damage during storms. Using a small volume hardness test, nanoindentation, on coral cores, we can examine changes in the physical properties of coral skeletons over time. We observe decreased skeletal stiffness and hardness during the 2010 coral bleaching event. Moreover, the submicron scale of nanoindentation facilitates comparison with Scanning Electron Microscopy (SEM) and Electron Backscatter Diffraction (EBSD). Using these tools, we can image aragonite crystals and map their orientation, helping to explain changes in coral hardness and stiffness at the submicron scale. Images generated develop two dimensional arrays representing the data in an intuitive fashion, which could be used by artists to convey critical messages of coral resilience.

The authors have worked in the past with artists and communications experts to generate videos for the general public, explaining their work collecting coral cores to understand the history of environmental conditions in the ocean and their impacts on coral reefs.