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Mussel study turns tide on role of warming on coast
ecosystem
11/01/02
RICHARD L. HILL
A warmer climate may mean bad news for mussels and other organisms that dwell
along Oregon and Washington's biologically rich shores, a new study suggests.
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The study's findings, described in today's issue of the journal Science, run counter to
the notion that tide pool creatures would be more stressed by rising temperatures in
already warm southern waters than in the Pacific Northwest's cooler northern latitudes.
But that conventional wisdom doesn't hold water, says Brian Helmuth, a marine
biologist at the University of South Carolina who led the study.
The problem is that summer's low tides in the Northwest tend to occur in the middle of
the day, exposing mussels to high temperatures that can cause them to overheat.
Mussels on Southern California's coast during the summer are more protected from the
heat because the low tides tend to be at night.
"This is one of the surprises of the study," Helmuth said. "The animals are as stressed
or more stressed in the summer on the central Oregon coast as they are in Santa
Barbara, California. Our study suggests a fundamental shift in where we should look
for effects of climate change in a model ecosystem and shows that we cannot focus
only on southern sites."
Helmuth and his study colleagues said the next three to five years may be especially
perilous for Northwest mussels. Low-tide exposure times are expected to increase
because of shifts in the moon's orbit, which influences tides, and other factors.
"Exposures at northern sites will be the highest they have been in 20 years, and
exposure at the southern sites will be the lowest they've been in that time," he said.
"So the most likely places that we're going to see effects of climate change in the
intertidal zone will be places such as Friday Harbor in Washington and possibly areas
of the central Oregon coast."
In their study, the researchers recorded temperatures at eight intertidal sites from near
Santa Barbara in the south to Tatoosh Island off the northwest tip of Washington's
Olympic Peninsula. Oregon sites in the study were at Boiler Bay north of Depoe Bay
and at Strawberry Hill south of Yachats.
The temperature-monitoring instruments were modified to have similar characteristics -weight, size and color -- as the mussels. "Air temperature is a poor predictor of animal
body temperature," Helmuth said, "so we set the instruments directly in the mussel
beds to get the same temperatures that the animals experience."
In the course of a summer day, mussels in Northwest intertidal areas are covered with
chilly water at high tides and are exposed to direct sunlight at low tides. "It's amazing
what temperature differences they experience," Helmuth said. "We can see increases
in temperatures of more than 40 to 45 degrees Fahrenheit in a matter of a couple of
hours."
Helmuth, who received his doctorate from the University of Washington, emphasized
that the study does not provide evidence for or against global warming. "What we're
asking is that if climate changes for any reason, whether it be an El Nino or global
warming or whatever, where would we see the effects?"
The researchers said two large mortality events were observed this past summer, one
at Seal Rock between Newport and Waldport, and the other at Friday Harbor. Helmuth
said high temperatures were the most likely culprit for the mussel deaths.
Jane Lubchenco, a professor of marine biology at Oregon State University who
specializes in intertidal zones, called the study's findings significant because they "put
to rest the simplistic notion that species at the supposed warmer end of their ranges
would be more stressed in a warmer world and would decline, while those at the cooler
end would expand their boundaries northward."
Lubchenco, who was not one of the study's researchers, said the findings "are likely
applicable to other shores around the world. One could look at how the tides interact
with the hottest times of the year and make some preliminary guesses about which
portions of species' ranges would likely be most at risk."
Helmuth said the study sites would continue to be monitored, with new sites added in
Alaska. Other researchers involved in the study included Christopher Harley of the
University of Washington and Stanford University; Patricia Halpin of Oregon State
University and the University of California at Santa Barbara; Michael O'Donnell of
Stanford; and Gretchen Hofmann and Carol Blanchette of UC Santa Barbara.
Funding for the study came from the National Science Foundation and National
Geographic. Helmuth credited the Partnership for Interdisciplinary Studies of Coastal
Oceans based at OSU and three other universities for providing "critical" logistical
support. Richard L. Hill: 503-221-8238; [email protected]
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