Studying corals that naturally persist in extreme environments can improve our understanding of the mechanisms corals require to survive under adverse environmental conditions. Here, we studied corals living in a mangrove lagoon in Bourake, New Caledonia, where pH remains persistently low (smaller 7.8, reaching 7.2), temperatures exceed 33C, and oxygen levels regularly fall below 2.5 mgL-1, and compared them to their conspecific counterparts at adjacent reef habitats. We examined differences in holobiont physiology and microorganism composition (bacteria) between habitats for Acropora muricata, A. pulchra, and Porites lutea.