From:The Portland Oregonian
December 06, 2002

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."