Benthic monitoring and sampling design and effort to detect spatial changes: a case study using data from offshore wind farm sites

Abstract

tThe exploitation of renewable energies, in particular offshore wind farms (OWFs), is an expanding sectorwhich involves activities that may adversely affect the marine benthic ecology. Fit-for-purpose mon-itoring is required with sufficient statistical power to detect ecologically meaningful changes, but todate there have been no studies on the suitability of monitoring programmes applied to OWFs. The the-oretical relationship of sampling effort with precision in community estimates and sensitivity of theanalysis in detecting spatial changes was investigated, this latter assessed through power analysis. Ben-thic community monitoring strategies and descriptors applied to UK OWFs were used to interrogate realdata variability in the marine environment. There was a general lack of clarity in the survey rationaleand hypotheses tested within OWF monitoring programmes hence a lack of rigour in the survey designand statistical testing. Consequently the statistical properties of monitoring strategies have been rarelyassessed. Precision of mean estimates of benthic community descriptors and the sensitivity in detectingdifferences in the means increased with sampling effort. At the average sampling effort applied in theOWF case studies (4 stations per impact type area and 3 replicates per station), the studies had sufficientpower to detect a ≥50% change between areas in mean benthic species richness (S; 5 species). Due totheir higher variability than S, more stations per impact type area were required to reliably detect a ≥50%change between areas in mean benthic abundance (N; 5 stations) and mean biomass (B; 10 stations).Higher sensitivity and precision of estimates of S, N and B was achieved with transformation of data.Understanding the general implications of monitoring design on the sensitivity of the detection of spatialchanges is important, particularly when monitoring effort has to be adjusted due to logistic and financialconstraints. Although there is no ‘one-size-fits-all’ approach to marine environmental data acquisition,this study guides researchers, developers and regulators in optimising benthic monitoring strategies atOWFs.