Long-term signal of disturbance:: Fucus gardneri after the Exxon Valdez oil spill

We followed long-term dynamics of a conspicuous intertidal brown alga, Fucus gardneri, for seven years after the 1989 Exxon Valdez oil spill (EVOS) in Prince William Sound, Alaska, USA. We compared percent cover of Fucus over time at sites that had been oiled, some of which were washed with high-pressure hot water relative to sites that had experienced neither oil nor cleanup activities (reference sites). Fucus cover at spill-disturbed sites was initially reduced due to toxic: effects of oil and cleanup but rapidly increased to above normal levels and then subsequently dropped in 1994-1995. The changes in cover at spill-disturbed sites were dramatic (greater than or equal to 50% decline year-to-year) and synchronous across all quadrats at a site. In contrast, reference sites demonstrated little synchrony. We examined two possible mechanisms that could generate synchronous fluctuations at spill-disturbed sites, i.e., (1) plant-herbivore coupling, in which limpet or snail grazing would reduce Fucus populations (hypothesis tested by analyzing abundances from 1990 to 1996), and (2) a single cohort of Fucus recruiting soon after the spill that would monopolize space for several years before declining synchronously (hypothesis tested by analyzing size frequency in 1996). We found no evidence for the first mechanism but support for the latter. The persistent patterns in size structure and dynamics in Fucus after EVOS suggest that full recovery had not occurred by 1996, even though Fucus cover at spill-disturbed sites was similar to reference areas within a few years of the spill.