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 (Ն50% 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 spilldisturbed 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.

Examination of the covering reaction (masking or heaping with shells) of Lytechinus anamesus in response to ultraviolet irradiation, sunlight, and surge suggests that most previous hypotheses explaining this reaction are inadequate or incomplete. Shaded L. anamesus initially reacts to short wavelength ultraviolet light (254 nm) with a fairly strong masking response, which is followed by death after an exposure of several days. Long wavelength ultraviolet light (360 mm) elicits moderate covering, while the nonirradiated controls rarely covered. These responses to ultraviolet light are probably artifacts, as L. anamesus and other sea urchins are seldom exposed to that factor in nature. There is a strong and immediate covering response to direct sunlight. Application of surge induces a cover response nearly equal to that of sunlight, regardless of light conditions. The intensity of covering during periods of surge appears to increase during the exposure period. Cessation of surge results in a rapid reduction in covering and a marked increase in movement. We suggest that covering is important in increasing the stability of this echinoid during periods of increased surge by effectively increasing its specific density, reducing its surface area, and changing the configuration it presents to surge forces. Sunlight intensity may be used as a cue that indicates directly the risk of displacement by surge action.

Several studies conducted in Prince William Sound during 1989 were directed at assessing short term biological effects of treatment methods considered or employed for treating oil contaminated beaches. The four treatment alternatives evaluated in this paper are: low pressure warm water wash (LP-WW); high pressure hot water wash (HP-HW); the dispersant Corexit 7664; and the beach cleaner Corexit 9580 M2. Effects on the biota were assessed primarily on the basis of changes in the abundance of dominant taxa and the magnitude of selected community attributes (such as percent cover by algae or animals, and number of taxa). Significant reductions in one or more community or population attributes, and increases in the percent of dead mussels were observed in response to all types of treatment but the strongest and most consistent effects were observed following high pressure hot water treatment, which was also accompanied by heavy mortality in rockweed. Generally, the programs were not designed to discriminate among the potential causes of damage. However, available data suggest that neither chemical nor LP-WW treatments caused significant thermal impacts in the intertidal biota. In contrast, temperature appeared to cause significant mortality in the dominant plants and grazing and filter-feeding animals in HP-HW treatment sites. Observations of displacement and mortality for clams and mussels suggest that physical effects may be substantial in some cases. Of the types of treatment examined, dispersant and beach cleaner treatments appeared to be accompanied with the smallest number of significant changes in abundance; however, this conclusion is weak because the LP-WW wash accompanying chemical applications during the tests was sometimes less rigorous than when performed by itself. LP-WW treatment was accompanied by an intermediate level of changes whereas HP-HW treatment was accompanied with the highest percentage of changes, nearly all of which were decreases. Based upon long term surveys in the area, HP-HW treatment caused severe and persistent effects that remained conspicuous as late as July 1992. The long term consequences of dispersant and beach cleaner applications have not been evaluated.

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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 (≥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.