Understanding the structural and mechanical properties of coral skeletons is important to assess their responses to natural and anthropogenic challenges and to predict the long-term viability of hermatypic corals in a changing ocean. Here, we describe the microstructure of the critically endangered staghorn coral (Acropora cervicornis) skeleton and its mechanical properties, spectral and fluidic behavior, including uniaxial compressive strength, resistance to plastic deformation, spectral vibrational response, and flow-field analysis. We evaluated skeletons of A. cervicornis retrieved from a nursery off Broward County, Florida, USA. Optical micrographs and X-ray computed topography revealed a complex system of canals and pores that allow rapid skeletal elongation while retaining sufficient strength to withstand currents, waves, and other physical forces. Compressive loading of the aragonite skeleton resulted in complex stress–strain deformation behavior; the unique pore arrangement resisted catastrophic cracks and prevented instantaneous failure. Vickers microhardness was 3.56 ± 0.31 GPa, which is typical for soft aragonite materials yet sufficient to withstand the hydraulic pressure of ocean waves. Impressions made by the diamond indenter had almost no cracks radiating from their corners, which again demonstrated the ability of the complex skeleton microstructure to suppress crack formation and growth (e.g., from the bites of grazers). Maps of the ν1 mode Raman peak of identation surfaces showed evidence of residual strain. However, the ν1 peak’s position barely changed (from 1083.6 cm−1 outside the impression to 1083.9 cm−1 in the center), indicating weak stress sensitivity. Flow-field analysis revealed small-scale, counter-rotating vortices formed in the skeleton’s wake, which can entrain food particles within range of polyp tentacles and facilitate transport of respiratory gases and wastes. Considered together, our results demonstrate that the perforate skeleton of A. cervicornis is well-adapted to withstand physical forces normally encountered in its shallow-water habitat, but may be susceptible to anthropogenic stressors that alter its architecture.

中文翻译：

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鹿角珊瑚 (Acropora cervicornis) 文石骨架的机械特性、光谱振动响应和流场分析

了解珊瑚骨骼的结构和机械特性对于评估它们对自然和人为挑战的反应以及预测雌雄同体珊瑚在不断变化的海洋中的长期生存能力非常重要。在这里，我们描述了极度濒危的鹿角珊瑚 (Acropora cervicornis) 骨骼的微观结构及其机械性能、光谱和流体行为，包括单轴抗压强度、抗塑性变形、光谱振动响应和流场分析。我们评估了从美国佛罗里达州布劳沃德县附近的苗圃取回的 A. cervicornis 骨骼。光学显微照片和 X 射线计算机地形图揭示了一个复杂的管道和孔隙系统，允许骨骼快速伸长，同时保持足够的强度来承受电流、波浪、和其他物理力量。文石骨架的压缩载荷导致复杂的应力应变变形行为；独特的孔隙排列可抵抗灾难性裂纹并防止瞬时失效。维氏显微硬度为 3.56 ± 0.31 GPa，这是软文石材料的典型硬度，但足以承受海浪的水压。金刚石压头形成的压痕几乎没有从角部辐射的裂纹，这再次证明了复杂的骨架微观结构抑制裂纹形成和扩展（例如，来自食草动物的咬伤）的能力。凹痕表面的 ν1 模拉曼峰图显示了残余应变的证据。然而，ν1 峰的位置几乎没有变化（从印模外的 1083.6 cm-1 到中心的 1083.9 cm-1），表示弱应力敏感性。流场分析显示，在骨骼尾迹中形成了小规模的反向旋转漩涡，这些漩涡可以在息肉触手范围内夹带食物颗粒，并促进呼吸气体和废物的运输​​。综合考虑，我们的结果表明，A. cervicornis 的有孔骨架非常适合承受通常在其浅水栖息地中遇到的物理力，但可能容易受到改变其结构的人为压力因素的影响。