SeaRover2018 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 2018 research cruise onboard Irish Lights Vessel Granuaile. Report contains 433 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: 27 dives encountered geogenic reef, 29 dives encountered biogenic reef, 17 dives hosted neither biogenic nor geogenic reef. This study revealed the following diversity along the surveyed parts of the seabed: 344 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); 86 OTUs were identified in the most species rich dive (D538/RB15); 3 OTUs were identified in the least species rich dive (D563/PB34); 52 OTUs were identified on the average dive; 9 OTUs were found in more than half of the transects; 55 OTUs were found in only one transect. 48 potential biotopes were identified in line with the Marine Habitat Classification for Britain and Ireland (v.15.03), of which: 43 are existing biotopes, un-altered from the MHCBI listing; 4 are potential new biotopes, or variant which may warrant becoming new child biotopes; 16 variant biotopes that follow the existing biotope descriptions, but variations of depth zones and morphologies were observed. None