Study finds NW frogs can skip sunscreen
From:The Portland Oregonian
December 06, 2002
by RICHARD L. HILL
Damaging rays in sunlight may be less of a threat to Northwest frogs than
previous research suggested.
A new study examined 136 potential breeding sites in the Oregon Cascades
and Washington's Olympics and found that the water was murky enough at
most locations to protect amphibian populations from harmful ultraviolet-B
radiation, or UV-B.
Scientists with the University of Washington, the U.S. Geological Survey
in Corvallis and the U.S. Environmental Protection Agency report their
findings in the current issue of the journal Ecology. Their focus did not
include the nationwide problem of malformed frogs, which has been linked
to a parasitic flatworm.
UV-B, which causes sunburn and skin cancer in humans, also has been found
to cause damage to amphibians. Biologists are concerned because the
thinning of the Earth's protective ozone layer in the upper atmosphere
allows for more of the damaging rays to reach the surface.
Earlier studies by Andrew R. Blaustein, an ecologist and zoology professor
at Oregon State University, and other scientists found in controlled field
and lab experiments that UV-B can kill or damage amphibian embryos.
But the new study indicates that the harmful rays at most Northwest sites
appear to be absorbed by the organic matter in the ponds, lakes and
wetlands where amphibians breed.
"Our data suggest that 85 percent of sites are naturally protected by
dissolved organic matter in pond water," the researchers said in their
report. "These data imply that UV-B is unlikely to cause broad amphibian
declines across the landscape of the American Northwest."
Daniel E. Schindler, one of the study's co-authors and an ecologist at the
University of Washington, said Blaustein and other researchers "have done
a wonderful job" in demonstrating the physiological impacts of UV-B on
amphibian hatching and development.
Schindler said the new study sought to expand on those findings by
determining whether the rays could cause amphibian populations to decline.
Frogs are a particularly good subject for study in that their growth or
decline can signal much about the health of broad ecosystems.
"On a site-specific basis, UV-B can be clearly very important," said
Schindler, an associate professor of zoology. "But if you ask what
proportion of those sites would get natural levels of UV that appear to be
physiologically harmful, it turns out to be a small proportion --
somewhere on the order of 15 percent of the sites had water clear enough
to allow enough UV to penetrate to make a difference."
Michael J. Adams, a research ecologist with the Geological Survey who
participated in the research, said the study "tends to diminish UV as a
major factor" in amphibian declines.
"It still needs to be considered, and it's going to be a factor in global
climate change," said Adams, who is with the Geological Survey's Forest
and Rangeland Ecosystem Science Center in Corvallis,
Levels of ultraviolet radiation usually are higher at mountain sites,
Adams said, but the study shows that the level of ray-absorbing organic
matter in the water "has a dramatic effect on UV exposure in the aquatic
portion of an amphibian's life."
Much of the dissolved organic matter comes from decomposing vegetation
that is washed out of nearby soils into surface and groundwater.
"It turns out that a little dissolved organic matter can go a long way in
screening out the UV," Schindler said.
Wendy J. Palen, the study's lead author and a UW zoology doctoral
candidate, said the 85 percent figure for locations that are buffered from
UV-B "is actually conservative," because the study just looked at
potential amphibian breeding areas. "If you just look at the sites where
amphibians are found, that figure would be higher because the amphibians
tend to breed in darker sites rather than in direct sunlight," she said.
Other researchers included Christopher A. Pearl and R. Bruce Bury of the
Geological Survey in Corvallis and Stephen A. Diamond of the EPA in
Duluth, Minn.
Blaustein said he stands by his previous research, saying at least two to
three dozen studies corroborate his results.
"Almost every single study -- regardless of whether UV is killing or not
killing eggs -- shows that exposure to UV even in tiny amounts does
something to these animals later on in life," Blaustein said. "We've shown
that it doesn't kill eggs of every species, but there are absolutely
sublethal effects, such as immune system problems and eye deformities.
"It's ridiculous to dismiss UV-B as a significant problem with
amphibians."
Copyright 2002, Portland Oregonian
|