Peterson_et_al_2003

Peterson_et_al_2003 - REVIEW Long-Term Ecosystem Response...

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Long-Term Ecosystem Response to the Exxon Valdez Oil Spill Charles H. Peterson, 1 * Stanley D. Rice, 2 Jeffrey W. Short, 2 Daniel Esler, 3 James L. Bodkin, 4 Brenda E. Ballachey, 4 David B. Irons 5 The ecosystem response to the 1989 spill of oil from the Exxon Valdez into Prince William Sound, Alaska, shows that current practices for assessing ecological risks of oil in the oceans and, by extension, other toxic sources should be changed. Previously, it was assumed that impacts to populations derive almost exclusively from acute mortal- ity. However, in the Alaskan coastal ecosystem, unexpected persistence of toxic sub- surface oil and chronic exposures, even at sublethal levels, have continued to affect wildlife. Delayed population reductions and cascades of indirect effects postponed recovery. Development of ecosystem-based toxicology is required to understand and ultimately predict chronic, delayed, and indirect long-term risks and impacts. B efore the Exxon Valdez oil spill, infor- mation available for constructing risk assessment models to predict ecologi- cal impacts of petroleum hydrocarbons was limited to selective, largely short-term monitoring after previous oil spills and to tests of acute toxicity in laboratory-tolerant taxa ( 1 ). After the tanker Exxon Valdez grounded on Bligh Reef in northern Prince William Sound on 24 March 1989, the magnitude of the spill, extent of shoreline contamination, and evident high mortality of wildlife prompted an evaluation of eco- logical impacts of unprecedented scope and duration extending now for more than 14 years ( 2 5 ). The release of 42 million liters of Alaskan North Slope crude oil contami- nated to some degree at least 1990 km of pristine shoreline. Prince William Sound was most severely affected, but the oil spread more than 750 km to the southwest along the Kenai Peninsula, Kodiak archi- pelago, and the Alaska Peninsula (Fig. 1). Years of study provide a new understand- ing of long-term biological impacts and recovery processes in a coastal ecosystem populated by abundant marine mammals, seabirds, and large fishes ( 2 5 ). Delays in recovery and emergence of long-term impacts are understood by bringing an ecosystem perspective to ecotoxicology ( 6 ). The ecosystem framework extends eco- toxicology to include interactions among multiple abiotic and biological components rather than treating each species separately and restricting assessment to acute short-term impacts ( 7 ). Disagreements exist between Exxon- and government-funded scientists ( 8 ), and unknowns persist, especially in un- derstanding how multiple processes com- bine to drive observed dynamics. Neverthe- less, these uncertainties do little to diminish the general conclusions: oil persisted be- yond a decade in surprising amounts and in toxic forms, was sufficiently bioavailable to induce chronic biological exposures, and had long-term impacts at the population level. Three major pathways of induction of long-term impacts emerge: (i) chronic per- sistence of oil, biological exposures, and population impacts to species closely asso-
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Peterson_et_al_2003 - REVIEW Long-Term Ecosystem Response...

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