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Benthic biodiversity and food web recovery post-decommissioning of oil and gas structures

benthic biodiversity,food web,offshore energy infrastructure,decommissioning,contamination,North Sea

Session 14 - The importance of benthic fauna in a changing Ocean

Offshore oil and gas structures approaching the end of their economic purposes are required to be partially or fully removed in the North Sea. Emerging evidence argues that these structures could provide beneficial ecological effects similar to artificial reefs or marine protected areas. This study used industry monitoring surveys to quantify the pre- and post- decommissioning effects on the benthic communities. Communities near NW Hutton showed signs of recovery five years after the decommissioning with an increase in total individuals and the proportion of top predators, leading to greater species richness and food web complexity. Communities near drilling wells were adversely impacted within 1 year of decommissioning with fewer species and simplified but more connected food webs. Communities near wells within 3 years post-decommissioning showed signs of recovery with more individuals and proportion of intermediate species, while declining average body mass and proportion of top predators implied such recovery was incomplete and negatively affected larger organisms. While sediment granulometry maintained stable pre- and post- decommissioning, metals (e.g., Barium) in the sediment persisted longer than the total hydrocarbon near the structures. These findings indicate that beneficial effects of decommissioning of oil and gas structures occur on quinquennial timescales and highlight the importance of industry undertaking periodic surveys and monitoring to collect more extensive biological data before and after decommissioning to improve the generality in other regions.