Coral gardens are considered to be hotspots of biodiversity and ecosystem functioning, due to the important structural and biogeochemical role of cold-water coral (CWC) species. Despite an increase in studies on deep reef-forming species, information on cold-water octocoral species is still very scarce. The present study focused on the feeding biology of two habitat-forming octocoral species typically encountered in seamounts in the Azores between 200 and 600m of depth: Dentomuricea aff. meteor and Viminella flagellum. We used an experimental approach aiming at determining the ability of the species to utilize different food sources including live phytoplankton (the diatom Chaetoceros calcitrans), Dissolved Organic Carbon (DOC) and live zooplankton (the rotifer Branchionus plicatilis). Food sources were isotopically enriched with tracers (13C, 15N) which allowed to trace the ingested food in different physiological processes, such as tissue incorporation, Dissolved Inorganic Carbon (DIC) respiration and excretion of Particulate Organic Carbon (POC) and Particulate Organic Nitrogen (PON).