Sampling design begets conclusions: the statistical basis for detection of injury to and recovery of shoreline communities after the ‘Exxon Valdez’ oil spill

• Published in: Marine ecology. Progress series (Halstenbek) 2001-01, Vol.210, p.255-283
• Main Authors: Peterson, Charles H., McDonald, Lyman L., Green, Roger H., Erickson, Wallace P.
• Format: Article
• Language: English
• Subjects: Animal, plant and microbial ecology; Applied ecology; Aquatic habitats; Balanoidea; Biological and medical sciences; Biota; Chthamalus dalli; Design analysis; Ecotoxicology, biological effects of pollution; Exxon Valdez; Fucus; Fundamental and applied biological sciences. Psychology; Geographic regions; Geography; Habitat selection; Habitats; Hazardous waste; Marine; Marine and brackish environment; Oil spills; REVIEW; Shorelines; Tectura persona; USA, Alaska
• ISSN: 0171-8630; 1616-1599
• DOI: 10.3354/meps210255

The joint effect of multiple initial decisions made about sampling design in evaluation of environmental impacts using observational field assessments influences the ability to detect and accurately estimate responses. The design can dictate in advance whether the study can identify even large impacts that truly exist. Following the ‘Exxon Valdez’ oil spill in 1989, 4 separate studies of effects of the spill on the intertidal biota were conducted. Studies overlapped sufficiently in geographic area, shoreline habitat, and biological response variables to permit contrasts showing how the aggregate of multiple design decisions led to differences in conclusions. The SEP (Shoreline Ecology Program) supported by Exxon and the CHIA (Coastal Habitat Injury Assessment) funded by the Exxon Valdez Oil Spill Trustee Council shared a core approach of establishing a stratified random design of site selection. The Exxon-supported GOA (Gulf of Alaska) study and the NOAA (National Oceanographic and Atmospheric Administration) Hazmat (Hazardous Materials) study both chose to employ subjective choices of fixed sites. Despite many common goals, these 4 studies differed greatly in: (1) sampling effort (area covered per sample quadrat, sample replication within sites, numbers of study sites per category, numbers of samplings, and total areas sampled) and sampling design (philosophy of targeting sampling effort, complete randomization versus matched pair designs, sampling frame, treatment of habitat heterogeneity within sites, interspersion of sites, and control of shoreline treatment and oiling intensity); (2) analytical methodology (analysis of covariance versus paired designs, treatment of subsamples as replicates inF-ratios, logic of inferring recovery, and power calculations); and (3) choice of biological response variables (taxonomic level of analysis, aggregating versus splitting separate communities, and scope of communities and habitats examined). The CHIA and NOAA Hazmat studies of epibiotic responses in sheltered rocky shores of Prince William Sound made several decisions to enhance detection power and produced similar conclusions about large reductions in total biotic cover of intertidal space,Fucuscover, mussel abundance, abundance of the limpetTectura personaand a balanoid barnacle, and increases in open space and abundance of an opportunistic barnacle,Chthamalus dalli. In contrast, the SEP study of this same habitat and geographic region adopted design choices res