WA4 Indirect Effects of Stressors on Organisms and Communities
204 Oregon Ballroom
8:00 AM - 12:00 PM, Wednesday
() Indirect Ecological Effects of the Exxon Valdez Oil Spill.
Neff, J1, Gilfillan, E2, 1 Battelle Momorial Institute, Duxbury, MA, USA2 Bowdoin College, Brunswick, ME, USA
ABSTRACT- Many processes identified as cascades of indirect effects following an oil spill are, instead, manifestations of climate oscillations or of the process of ecosystem recovery through succession. Several cascades of indirect effects were postulated for the 1989 Exxon Valdez oil spill in Prince William Sound (PWS), AK. However, field studies reveal that the indirect effects are within the range of natural variability in the PWS environment and are ecologically insignificant. Populations of most intertidal species declined on the most heavily oiled and intensively cleaned shores, but recovery was rapid, with few oscillations in community abundance and composition. This was because the rocky intertidal community is adapted to natural disturbance and does not include invertebrates that graze on the keystone species, rockweed. Some wild-run pink salmon were exposed to oil during the year after the spill as embryos and alevins in the intertidal reaches of streams or as fry and juveniles in nearshore waters. It has been hypothesized that this exposure may have reduced growth rate, leading to increased predation and lower at-sea survival. However, field studies document normal survival and growth of embryos and juveniles in the spill zone; postspill wild-run pink salmon escapements are similar to the prespill numbers. Between 20 and 40% of sea otters in the spill zone of PWS were killed by direct exposure to the oil in 1989. It was speculated that the reduction of sea otter numbers would lead to destruction of the kelp forest ecosystem through overgrazing by sea urchins, a favorite food of otters. This trophic cascade was not detected in PWS. These three examples covering rocky shores, wild-run salmon populations, and the shallow coastal ecosystem where the sea otter is the keystone species confirm that indirect effects of the Exxon Valdez spill were ecologically insignificant.
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