University of Washington - W Arm

Restoration Project

University of Washington - W Arm

Restoration Objective:

This study aimed to determine the mechanisms behind changes in cover at spill-disturbed sites that were dramatic and synchronous across all quadrats at a site. This study examined two possible mechanisms that could generate synchronous fluctuations at spill disturbed sites; 1) plant-herbivore coupling, in which limpet or snail grazing would reduce Fucus populations; or 2) a single cohort of Fucus recruiting soon following the spill that monopolised for several years before declining synchronously.

Site Selection Criteria:

Rocky mid-intertidal sites were chosen for accessibility and comparability in the semi protected rocky habitat type.

Cause Of Decline:

On 24 March 1989, the tanker T/V Exxon Valdez spilled 36000 Mg of oil, which eventually contacted 10–20% of shoreline in Prince William Sound, Alaska. After this event, adult Fucus gardneri, an intertidal brown algae, were coated with oil but did not necessarily die. Part of the clean-up effort involved washing shorelines with large volumes of high-pressure hot seawater (60C) to lift oil off the shore. This treatment caused 90% mortality of adult Fucus and probably scalded much of the rock surface, killing any remaining germlings as well. Intertidal invertebrates, some of which consume Fucus, also disappeared.

Key Reasons For Decline:

Water Pollution

Scientific Paper

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

W.B. Driskell, J.L. Ruesink, D.C. Lees, J.P. Houghton, S.C. Lindstrom
Ecological Applications, Vol. 11.
https://doi.org/10.2307/3061118

Organisation:

University of Washington

Site Observations:

Observation Date

1st Jan 1989 – 1st Jan 1996

Action Summary:

Percentage cover of Fucus gardneri was measured over time in areas affected by the 1995 Exxon Valdez oil spill. Cover was compared between areas that had experienced oil spills (some of which had been washed with hot seawater at high pressure to remove oil) and areas with no oiling or clean-up activities (reference sites). Herbivore abundance and Fucus size classes were also measured.

Lessons Learned:

There were reference sites used as controls, but they exhibited a lot of unexplained variation during the study period.

Project Outcomes:

Fucus cover at spill-disturbed sites was initially reduced due to toxic effects of oil and clean-up but then 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. There was evidence that this pattern resulted from a single cohort of Fucus that recruited soon after the spill and monopolised space for several years before declining synchronously. The persistent patterns in size structure and dynamics in Fucus after the spill 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.

Key Reasons For Decline:

Water Pollution

Indicator Data:

Indicator:

Ending Value:

Starting Value:

Kelp Cover

21.7105
%
33.5526
%
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