World amphibian populations plummet toward extinction
The decline of the species could be a signal that the health of planet Earth is being jeopardized, according to scientists
Saturday, February 19, 2000
By Richard L. Hill of The Oregonian staff
WASHINGTON, D.C. -- Frogs, toads, salamanders and other amphibian populations have been mysteriously dying in Oregon for years.
But now the species decline is being documented around the world. Fourteen species of amphibians have disappeared from Australia in recent years. The golden toad has become extinct in Costa Rica, and other amphibian declines have been recorded in Europe, South America, Asia and Africa.
Amphibians are extremely sensitive to their environment, and their decline possibly could be a signal that the planet's health is being jeopardized, according to scientists who talked about the issue during an international scientific conference Friday.
The combined reports, which document that frogs are in trouble around the world, worry biologists, including an Oregon State University researcher who has been raising a red flag on this issue for several years.
"The overall result is that this group of animals, which has been around since the time of the dinosaurs, is now in serious decline all over the world," said Andrew R. Blaustein, a zoology professor at OSU. "And some of the things that are killing frogs almost certainly have implications for other animal species, including humans."
Causes include insecticides, crop fertilizers, weather and viruses. One cause might not be enough to bring on death or deformity, Blaustein said, but a combination of factors could work to cripple some populations.
"Finding out exactly what is causing die-offs is an incredibly complex problem and requires intensive study," Blaustein said. "Amphibian species vary tremendously, so what might kill one frog might not kill another."
Already, five species in the Northwest are listed as candidates for the endangered species list, including the Cascades frog, the red-legged frog, the Oregon spotted frog, the Columbia spotted frog and the Western toad.
"We're trying to find out what variables are at work to cause these significant declines and even some species' extinction. We're looking at everything from microscopic viruses to global climate change," James P. Collins, a biologist at Arizona State University, said at the annual meeting of the American Association for the Advancement of Science in Washington, D.C. The agency is the oldest and largest general-science organization.
Although human encroachment on wetlands and other amphibian habitat is considered the primary cause for the animals' decline, the biologists reported other culprits that are either causes or suspects:
Outbreaks of a lethal chytrid skin fungus that has been found in Washington, Colorado, California, Illinois, Australia, and Central and South America.
A fungus called Saprolegnia, which has turned up in Oregon, can kill larvae and adult amphibians.
Non-native predators, such as voracious bullfrogs and trout, that kill native amphibian species.
Pollutants, such as herbicides, insecticides and crop fertilizers.
All of these destructive factors have been found in Oregon, except for the chytrid skin fungus. In recent years, Blaustein also has found that the rising level of UV-B radiation in sunlight caused by the thinning of the Earth's protective ozone layer is taking its toll on salamander eggs in Cascade ponds and lakes. He also published a study in 1998 that linked an increase in UV-B radiation to eye damage in the Cascades frog.
Blaustein and his OSU colleagues also reported recently that they have found another potential threat to Northwest amphibians: nitrogen-based compounds found in crop fertilizers. Their study, which was published in the journal Environmental Toxicology and Chemistry, found that some tadpoles and young frogs exposed to modest amounts of nitrates and nitrites -- levels considered safe in human drinking water -- developed abnormalities and died. They found that the imperiled Oregon spotted frog was the most sensitive to the compounds.
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