Using Industrial Remotely Operated Vehicles in Stand-by Time for Deep-water Biodiversity Assessment: A Case Study From Offshore Nigeria

Abstract Description There is very limited information available on the deep water biodiversity offshore Nigeria. Detailed information on seabed communities is vital for effective environmental management of offshore drilling disturbance but collection of environmental data usually require a dedicated research vessel and associated high costs. We present an approach to environmental survey that uses remotely operated vehicles (ROVs), already in place on survey/supply boats, during stand-by time in drilling operations for low-cost and high-quality operations. Application Spatially-referenced ROV video surveys were performed following a stratified random design. These, combined with targeted ROV sample collections (of biological specimens, sediment and rock), enabled an accurate quantitative census of biological patterns. Oceanographic data were collected with self-contained data-logging conductivity, temperature and depth sensors attached to the ROV. Results, Observations, and Conclusions ROV survey showed that the seabed environment offshore Nigeria (750-1350m water depth) was extremely diverse, containing several habitats from sedimentary plains to steep rocky slopes. The visible seabed fauna were generally abundant (0.3 animals m-2) and diverse (>69 species). Faunal communities varied in density and composition across the habitat and depth range. Many species were previously described; however, surveys revealed several potential new species and ROV traps captured a confirmed new species of amphipod crustacean. Sediment samples collected provide valuable pre-drilling baseline data, which will allow assessment of the extent and magnitude of future environmental disturbance from operations. Temporally replicated temperature and salinity depth profiles captured the thermocline's seasonal movement in much greater detail than previous observations. Significance of Subject Matter The significance of this biodiversity assessment includes: Data collected provided a suite of high-resolution baseline measurements which are invaluable for future impact assessment. Use of ROVs during stand-by time enabled rapid low cost data collection. Approach facilitates initial environmental evaluation and longer-term monitoring of hydrocarbon exploration and production areas. Results increase the knowledge of the environmental conditions of deepwater offshore Nigeria and indeed West Africa. This survey provided important information on offshore biodiversity to the Nigerian Regulatory Authorities (Federal Ministry of Environment and Department of Petroleum Resources) thus enhanced regulatory support for the drilling project.