Methane-related seafloor habitats and sediment microbiome at a cold-water corals site off the Vesterålen coast, northern Norway

Cold-water corals in the Hola area off the coast of Vesterålen (N. Norway), thrive on a substrate made of methane-derived carbonate and are closely associated with microbial mats. High resolution seafloor imagery and sediment samples collected during the EMAN7 expedition in June 2022 allowed us to reconstruct the spatial relationships between methane seepage and seafloor habitats and gain insights into subsurface biogeochemical processes directly influencing benthic ecosystems. Here, we present the fine-scale orthomosaics and habitat maps covering 1680 m² of seafloor in proximity to the coral mounds and the geochemistry (sedimentary carbon and nitrogen, pore waters) of a pushcore and blade core collected from a microbial mat and a reference area, respectively. The push core revealed the presence of a macroscopic microbial biofilm at 9 cm depth within the sediment, which is associated with a sharp drop in downcore δ¹³C of sedimentary organic matter and dissolved inorganic carbon and in C/N ratios. Results from 16S rRNA gene analyses conducted on the uppermost 10 cm of sediment in the pushcore showed a drop in alpha diversity and a compositional change from high abundance of ASVs representing Protebacteria to those representing Halobacterota that we ascribe to the occurrence of methanotrophic consortia performing anaerobic oxidation of methane

Acknowledgments: this research was funded by EMAN7 project (Research Council of Norway grant No. 320100) and supported by AKMA project (Research Council of Norway grant No. 287869) and EXTREMES (UArctic UA 06/2024)