Ecological recovery of benthic fauna from contamination near oil and gas platforms.

Many oil and gas platforms in the North Sea are nearing their end of life and there is an urgent need to understand the legacy effects of associated seabed contamination on benthic communities. We use data from industry-based monitoring surveys, 1985-2015, in a North Sea wide study to investigate change in contaminants and the biomass of benthic functional groups (small infauna, small mobile epifauna, infaunal macrobenthos, and epifaunal macrobenthos). Total hydrocarbon concentrations in sediment samples exceeded 150,000 μg/g between 1992 and 1998 and within 250 m of 6 different platforms. Statistical relationships between chemical concentration, distance from platform and year were modelled using Generalized Additive Mixed Models for 5 environmentally distinct clusters of 236 platforms. Non-linear decreases were identified for total hydrocarbon concentrations as distance from platforms increased for four clusters, but not the deep-water cluster to the north of Scotland. Similarly structured statistical models with benthic biomass as the response variable and total hydrocarbon concentration as the predictor showed that relationships between them varied among clusters and functional groups. Following management measures to reduce contaminant concentrations, the biomass of benthic groups has since returned to reference conditions across many sites. Our results provide a functional perspective that can support ecosystem modelling, inform environmental assessments and support the implementation of management measures.