Deep-sea megabenthic fauna type from ROV transects of MEDWAVES survey

Dataset encompasses identification and quantitative information on megabenthic fauna and substrate characterization resulted from the processing of ROV video transects acquired during the research expedition MEDWAVES (MEDiterranean out flow WAter and Vulnerable EcosystemS), as part of the H2020 European project A Trans-Atlantic assessment and Deep-Water Ecosystem-Based Spatial Management Plan for Europe (ATLAS, https://www.eu-atlas.org/). This data were collected at four geomorphological features that represent different types of seafloor elevations, covering a gradient of influence of the Mediterranean Outflow Water (MOW) from the western Mediterranean to the central North Atlantic: The Seco de los Olivos bank (SdO) in the Alboran Sea (Western Mediterranean), the Gazul mud volcano (GMV) in the Gulf of Cádiz, the Ormonde seamount (OS) in the Portuguese margin and the Formigas seamount (FS), SE Azores. To obtain quantitative data, a series of still images were captured from the video footage of ROV video transects at 5 m intervals. Each record at the datasets (fauna and substrate) represent a georreferenced still image. Images with poor quality (i.e., sediment resuspension, lack of focus, ROV too far from the seafloor, close-ups for species identifications and not visible lasers, sampling events) were disregarded for the analyses. At each still image, the abundance (total count) of species or operational taxonomic units (OTUs) (fauna dataset) and the percentage (from 0 to 20) of each substrate type (substrate dataset) were recorded.