SeaRover2019 ROV (Remote Operated Vehicle) Deep Water Reef Habitat & Species Video Analysis report produced by Giulia La Bianca, Rebecca Ross and Kerry Howell (University of Plymouth) and Commissioned by Marine Institute, Rinville, Oranmore, Co. Galway. This report describes ROV Holland (Marine Institute, Ireland) underwater video data collected during SeaRover 2019 research cruise onboard RV Celtic Explorer. Report contains 246 pages. SeaRover stands for Sensitive Ecosystem Assessment and ROV Exploration of Reef. This survey was commissioned by the National Parks and Wildlife Service (NPWS), funded by the European Maritime and Fisheries Fund (EMFF), and coordinated and led by INFOMAR (Integrated Mapping for the Sustainable Development of Ireland?s Marine Resources) and Ireland?s Marine Institute. This technical report provides a detailed ecological analysis of 52 ROV dives: 13 dives encountered geogenic reef, 5 dives encountered biogenic reef, 39 dives hosted neither biogenic nor geogenic reef. This study revealed the following diversity along the surveyed parts of the seabed: 246 putative species were identified from HD video footage supplemented by high resolution imagery (using operational taxonomic unit (OTU) system as it is not always possible to identify fauna to species level); 82 OTUs were identified in the most species rich dive (D696/T13); 12 OTUs were identified in the least species rich dive (D683/T52); 32 OTUs were identified on average from each dive; 1 OTU was found in more than half of the transects; 61 OTUs were found in only one transect. Potential biotopes were identified in line with the Marine Habitat Classification for Britain and Ireland (v.15.03), of which: 40 are existing biotopes, un-altered from the MHCBI listing; 5 variant biotopes that follow the existing biotope descriptions, but variations of depth zones and substrata were observed. To present results of deep water reef habitat and species video analysis based on underwater video data collected during SeaRover 2019 survey onboard RV Celtic Explorer. None