Resilience of cold-water coral holobionts to thermal stress

Abstract

Cold-water corals are threatened by global warming, especially in the Mediterranean Sea where they live close to their upper known thermal limit (i.e. 13°C), yet their response to rising temperatures is not well known. Here, temperature effects on <i>Lophelia pertusa</i> and <i>Madrepora oculata</i> holobionts (i.e. the host and its associated microbiome) were investigated. We found that at warmer seawater temperature (+2°C), <i>L. pertusa</i> showed a modification of its microbiome prior to a change in behaviour, leading to lower energy reserves and skeletal growth, whereas <i>M. oculata</i> was more resilient. At extreme temperature (+4°C), both species quickly lost their specific bacterial signature followed by lower physiological activity prior to death. In addition, our results showing the holobionts' negative response to colder temperatures (-3°C), suggest that Mediterranean corals live close to their thermal optimum. The species-specific response to temperature change highlights that global warming may affect dramatically the main deep-sea reef-builders, which would alter the associated biodiversity and related ecosystem services.