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An Ecosystem in Transition
The graph below shows changes in the area covered by one of the most abundant algae on the shorelines of Prince William Sound, Fucus gardneri, commonly called "rockweed" or "popweed." Because this algae favors the middle part of the tidal zone where much of the heavy oiling and cleanup occurred, it was significantly reduced in abundance in many areas of the sound. Beginning in 1990, we saw the cover of Fucus increase steadily at oiled sites--until 1994. In 1994, and continuing into 1995, there appeared to be a significant decline in cover, especially at sites that had been oiled.
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Comparison of rockweed cover at middle elevation unoiled sites and oiled/washed rocky sites, 1989-1996. Note
steep decline in cover at oiled/washed sites in 1989 after treatment, and steady decline in cover at oiled/washed
sites beginning in 1993. (Washed sites were cleaned by hot-water washing during the months after the spill.)
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What caused the decline in 1994 and 1995? We don't know for certain. Here are some possibilities:
- It is possible that shoreline treatment in 1989 killed existing stands of rockweed so that the normal mix of different age plants instead became dominated by plants that began growing the first year. What may have occurred in 1994 was simply a die-off of those plants that under normal circumstances would not be noticeable because there would be many other different ages of plants nearby.
- Alternatively, an explosion in the population of algal grazers two and three years after the spill may have had something to do with the decline. (For more information, see the link, Snail Grazer Abundance and Periwinkle Snails, below.)
- Perhaps it is a subtle, longer-term toxic effect of oiling.
- Or, it might have nothing at all to do with the spill or cleanup.
Data collected in the coming years will help to shed light on these conditions.
Ecological Peaks and Valleys
What do these kinds of trends over time mean for recovery in Prince William Sound? We think it suggests that peaks and valleys in abundance of plants and animals will continue as the system adjusts itself. With time, natural controls will dampen the oscillations in abundance of the biota. Much of this adjustment process will be subtle, and to the casual observer conditions will continue to look much as expected in an area that remains a very beautiful place to visit. However, these subtle changes may have implications for how we perceive the process of recovery. They also may ultimately affect other parts of the ecosystem that are commercially and aesthetically important. Our studies of the Sound will continue until 2005 in an effort to answer these questions.
For more information
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- Rockweed One of the most abundant algae on the shorelines of Prince William Sound is Fucus gardneri, commonly called "rockweed" or "popweed."
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- What about Salmon? Pink salmon harvests have also fluctuated dramatically in the years since the spill. Again, it's not clear just why.
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- What is Recovery? Ecosystems are constantly adjusting themselves. Against that background, how can we identify recovery?
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Other Pages in this Series
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