Recovery of deep-water megafaunal assemblages from hydrocarbon drilling disturbance in the Faroe-Shetland Channel

Recovery of megabenthic assemblages from physical disturbance at the Laggan deep-water hydrocarbon drilling site in the Faroe-Shetland Channel was assessed using remotely operated vehicle quantitative video survey. Twelve undisturbed control sites and 2 well sites (A and C, disturbed 3 and 10 yr prior to this work, respectively) were analysed and compared with a previous survey immediately following disturbance at A. The megabenthic epifauna at Laggan was dominated by sponges (69.6% total fauna) represented by 20 taxa. Cnidarians (12.8%; 9 taxa) and echinoderms (7.1%; 11 taxa) were also common. Diversity was generally high and typical for the cold waters of the Faroe-Shetland Channel. Two distinct assemblages were found: one in the deeper area of the study site (also incorporating Site C), and one in the other areas (incorporating Site A). Motile faunal densities and richness were significantly elevated immediately after drilling in an area with intermediate disturbance, presumably attracted to available carcasses of organisms killed by drilling disturbance. After 3 and 10 yr, densities of motile organisms were less variable with distance, except very close to drilling where densities and richness were still reduced. Sessile faunal densities and richness increased significantly with increasing distance from drilling in all years, although both metrics were significantly higher close to drilling after 3 and 10 yr when compared to immediately after drilling. These data suggest partial megabenthic recovery between 3 and 10 yr post-disturbance. Despite this, in the area remaining completely covered by drill cuttings there were few megafauna observed even after 10 yr.