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This study describes the biological results of a comprehensive shoreline ecology program designed to assess ecological recovery in Prince William Sound following the Exxon Valdez oil spill on March 24, 1989. The program is an application of the “Sediment Quality Triad” approach, combining chemical, toxicological, and biological measurements. The study was designed so that results could be extrapolated to the entire spill zone in Prince William Sound.
The spill affected four major shoreline habitat types in Prince William Sound: pebble/gravel, boulder/cobble, sheltered bedrock, and exposed bedrock. The study design had two components: (1) one-time stratified random sampling at 64 sites representing four habitats and four oiling levels (including unoiled reference sites) and (2) periodic sampling at 12 nonrandomly chosen sites that included some of the most heavily oiled locations in the sound. Biological communities on rock surfaces and in intertidal and shallow subtidal sediments were analyzed for differences resulting from to oiling in each of 16 habitat/tide zone combinations. Statistical methods included univariate analyses of individual species abundances and community parameter variables (total abundance, species richness, and Shannon diversity), and multivariate correspondence analysis of community structure.
The communities of animals and plants inhabiting the bedrock and coarse sediments on Prince William Sound's shorelines responded much differently to oiling than communities in soft-sediment environments that were the subject of a majority of shoreline studies conducted after other oil spills.
Sedimentary environments in Prince William Sound did not become anaerobic but showed evidence of increased biological activity as the oil residue became a source of organic carbon—without the usual succession of opportunistic invaders. Similarly, some bedrock sites showed increases in abundance, species richness, and diversity, as the spaces created by oiling were recolonized. This was to be expected in a high-energy environment dominated by “patch dynamics”; the rock surfaces and sediments support a mosaic of species that are adapted to rapidly colonize new spaces created by wave action and other physical factors.
Two measures of ecological shoreline recovery are reported: an upper-limit estimate based on univariate analysis of community parameters and a lower-limit estimate based on multivariate correspondence analysis of community structure. Overall, the results indicate that between 73% and 91% of the oiled shoreline in Prince William Sound was ecologically recovered (i.e., it was indistinguishable from reference) in the summer of 1990. These results reflect rapid recovery of the biological communities and are consistent with chemical and toxicological studies (this volume), which found that hydrocarbon-related toxicity was virtually absent in the shoreline sediments by 1990–1991.
Exxon Valdez, oil-spill effects, oil-spill recovery, shoreline ecology, stratified random sampling, generalized linear models, correspondence analysis, patch dynamics, rocky shores, boulder/cobble beaches, pebble/gravel beaches
Bowdoin College, Brunswick, ME
Bowdoin College, Brunswick, ME
West Virginia University, Morgantown, WV
Arthur D. Little, Inc., Cambridge, MA