Comparison of methods (ROV, diver) used to estimate the composition and abundance of biota colonizing an offshore oil platform: A pilot study

Offshore oil and gas platforms have a finite life of production operations. Once production ceases, decom-missioning options for the platform are evaluated. The role that a platform's jacket plays as invertebrate habitat may inform the decommissioning decision. Worldwide, few scientific surveys specific to marine invertebrates have been conducted at platforms to collect data needed for biological assessments; however, recent research has examined the biological community utilizing historical industry-collected Remotely Operated Video (ROV) im-agery that was not specifically collected for such purposes. To address concerns of bias in using video footage from industry structural surveys for biological assessments, we compared estimates of invertebrate density and species richness beneath a California oil platform determined using data from three sources: video from an in-dustry ROV "structural" survey, video from a scientific ROV "biological" survey using the same vehicle, and photoquadrat still imagery from a scientific scuba diver survey. All surveys were conducted along the same jacket crossbeams. We found that the epibenthic assemblages characterized by the two ROV methods were similar. More species were observed in the diver photoquadrats than in either of the two kinds of ROV surveys, because smaller and more cryptic species could be resolved. We cannot extrapolate from this preliminary, localized study to all platforms worldwide; however, our results indicate routine platform structural integrity surveys are as valuable as dedicated scientific biological surveys for macroinvertebrates and represent an invaluable source for opportunistic marine community assessments.