Forecasting the ecological legacy of aging offshore oil and gas platforms

Erin Meyer-Gutbrod, University of South Carolina, School of the Earth, Ocean & Environment, Columbia, United States, Milton Love, University of California Santa Barbara, Santa Barbara, CA, United States, Donna M Schroeder, Department of Interior, Bureau of Ocean Energy Management, Camarillo, United States and Robert J. Miller, University of California, Marine Science Institute, Santa Barbara, United States
Abstract:
There are currently thousands offshore platforms in place for oil and gas extraction worldwide, and decommissioning efforts over the next 3 decades are estimated to cost more than $200 billion USD. As platforms reach the end of their useful lifetime, operators and regulatory agencies will assess the environmental impact of potential decommissioning strategies. Among the many factors that will be weighed in preparation for these major economic and engineering challenges is the fate of the fish and invertebrate communities that inhabit the structures underwater. Offshore platforms act as de facto artificial reefs, and some are recognized as some of the most productive fish habitats in the global oceans. With several southern California platforms currently beginning the decommissioning process, we aim to use recent biological surveys to support decision making among three possible decommissioning scenarios: leave in place, partial removal at 26 m depth, and complete removal of the platform and underlying shell mound. We used fish density and size data from scuba and submersible surveys of the platforms from 1995–2013 to characterize community composition and estimate fish biomass and annual production. Bottom trawl surveys were used to characterize future fish assemblages at platform sites under the complete removal decommissioning scenario. We found that complete removal of a platform resulted in 95% or more reduction in the fish biomass and annual somatic production at the site. Partial removal resulted in far smaller losses, averaging 10% or less. In the event that all 24 surveyed platforms are completely removed, we relate the loss in fish biomass to commercial landings in the region. These potential losses of ecologically and economically important fish should be considered when evaluating offshore platform decommissioning options in the Southern California Bight. This approach could be used as a model for informing “rigs to reefs” discussions occurring worldwide.
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