Microbially mediated carbon utilization by a cold-water coral inhabiting methane seeps.

Deep-sea methane seeps fuel biodiverse habitats sustained by the release of hydrocarbon-rich fluids and associated microbial activity. Here, we describe the ecology of a seep-associated cold-water coral and provide evidence of its associations with chemosynthetic bacteria. High-resolution seafloor surveys revealed that the distribution of this coral was predominantly confined to actively seeping zones, and habitat suitability models confirmed that proximity to active seepage was an important factor influencing the coral’s distribution. Stable carbon-isotope values were consistent with a nutritional strategy incorporating chemosynthetically derived carbon, likely as a supplement to suspension feeding on photosynthetically derived material. Microbial metabarcoding confirmed the presence of both thiotrophic and methanotrophic bacteria, including SUP05 and MMG-2 groups. Incubations with 13C-labelled methane further revealed this species may also be capable of assimilating methane-derived carbon into its biomass. These findings provide new evidence of a previously underrecognized facultative symbiosis between cold-water corals and chemosymbiotic bacteria and suggest that these corals are not restricted to the periphery of seep habitats. Instead, they may exploit microbial associations, including contributions from both thiotrophic and potentially methanotrophic taxa, to persist in actively seeping areas.