Reef-building corals harbour an astonishing diversity of microorganisms, including endosymbiotic microalgae, bacteria, archaea, and fungi. The metabolic interactions within this symbiotic consortium are fundamental to the ecological success of corals and the unique productivity of coral reef ecosystems. Over the last two decades, scientific efforts have been primarily channelled into dissecting the symbioses occurring in coral tissues. Although easily accessible, this compartment is only 2-3 mm thick, whereas the underlying calcium carbonate skeleton occupies the vast internal volume of corals. Far from being devoid of life, the skeleton harbours a wide array of algae, endolithic fungi, heterotrophic bacteria, and other boring eukaryotes, often forming distinct bands visible to the bare eye. Some of the critical functions of these endolithic microorganisms in coral health, such as nutrient cycling and metabolite transfer, which could enable the survival of corals during thermal stress, have long been demonstrated. In addition, some of these microorganisms can dissolve calcium carbonate, weakening the coral skeleton and therefore may play a major role in reef erosion. Yet, experimental data are wanting due to methodological limitations. Recent technological and conceptual advances now allow us to tease apart the complex physical, ecological, and chemical interactions at the heart of coral endolithic microbial communities. These new capabilities have resulted in an excellent body of research and provide an exciting outlook to further address the functional microbial ecology of the "overlooked" coral skeleton.

中文翻译：

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深入骨髓：被忽视的内石微生物组在珊瑚礁健康中的作用。

造礁珊瑚拥有惊人的微生物多样性，包括内共生微藻、细菌、古生菌和真菌。这个共生联盟内的代谢相互作用对于珊瑚的生态成功和珊瑚礁生态系统的独特生产力至关重要。在过去的二十年里，科学努力主要用于剖析珊瑚组织中发生的共生关系。虽然很容易到达，但这个隔间只有 2-3 毫米厚，​​而下面的碳酸钙骨架占据了珊瑚的巨大内部体积。骨骼远非没有生命，而是含有大量的藻类、内生真菌、异养细菌和其他无聊的真核生物，通常形成肉眼可见的明显条带。这些内石微生物在珊瑚健康中的一些关键功能，例如养分循环和代谢物转移，可以使珊瑚在热应激期间存活，早已得到证实。此外，其中一些微生物可以溶解碳酸钙，削弱珊瑚骨架，因此可能在珊瑚礁侵蚀中起主要作用。然而，由于方法学上的限制，我们需要实验数据。最近的技术和概念进步现在使我们能够梳理珊瑚内石微生物群落核心复杂的物理、生态和化学相互作用。这些新功能带来了出色的研究成果，并为进一步解决“被忽视”珊瑚骨骼的功能微生物生态学提供了令人兴奋的前景。