EXTINCTION CRISIS FOR AMPHIBIANS
Frogs, toads and other species dying off -- new fungus magnifies environmental problems
David Perlman, Chronicle Science Editor
Friday, July 7, 2006
Email This Article
A strange new fungus disease that kills frogs and toads and every other species of amphibian is spreading around the globe and -- combined with pollution and overdevelopment -- is driving more and more of the creatures to extinction, a coalition of the world's top biologists warns.
At least one-third of the world's known amphibians are threatened by the combination of attacks, and up to 122 species have become extinct within the past 25 years, the international team of specialists is reporting in today's edition of the journal Science.
"Amphibian declines and extinctions are global and rapid," 50 of the world's leading specialists on water-dwelling animals declared in a joint report. At least 427 species are "critically endangered," they said.
The effects are being felt in California's High Sierra, where Berkeley scientists found that the disease is rampant and killing yellow-legged frogs and Yosemite toads, whose populations already are being strained by development and pollution.
While the spread of the disease is a major new threat to all amphibians, the scientists reported that the greatest current danger to every threatened species is still the loss of habitat as cities and suburbs expand, streams and ponds and wetlands give way to the needs of farmers, and forest lands are destroyed.
But the fungus, a unique species called Batrachochytrium dendrobatidis, could start taking on a larger role in the increasing extinction because of global warming, which scientists suspect is lowering amphibians' resistance to the disease.
The fungus was discovered in Australia and Panama only eight years ago and since then has spread across Europe and both the Americas, causing skin infections called chytrid disease in every amphibian species it attacks. The death rate from the infections is 100 percent, biologists have found. The disease, they concluded, "causes catastrophic mortality in amphibian populations, and subsequent extinctions."
UC Berkeley Professor David Wake and his wife, Marvalee, also a UC Berkeley professor, are involved in the research. As recently as last week, they were studying amphibian populations on the shores of lakes in the Ebbetts Pass area of the Sierra.
They swabbed the bellies and legs of frogs and toads and brought the swabs back to the lab in Berkeley, where they will be analyzed for the presence of the fungus. David Wake said the fungal disease is rampant there and infecting the skin of frogs and toads. The fungus is widespread in Yosemite and the Sequoia and Kings Canyon national parks as well, he said.
What alarms the scientists most about the new disease is the pace of its assault. Less than two years ago, Karen Lipps of Southern Illinois University led a research group in Panama that found the dead bodies of 346 frogs and five salamanders, killed by the fungus disease in less than four months.
"The high virulence and large number of potential hosts of this emerging infectious disease threaten global amphibian diversity," Lipps reported this year in the Proceedings of the National Academy of Sciences.
In Costa Rica's Cloud Forest Preserve of the Tropical Science Center, biologist J. Alan Pounds and his colleagues recently reported the total disappearance of the Monteverde harlequin frog, along with one golden toad species -- caused, he said in the journal Nature, by their increased susceptibility to chytrid disease as rising global temperatures have weakened their ability to resist the toxin.
The team of experts focusing more broadly on amphibian extinction estimates that nearly one-third of all 5,743 known amphibian species in the world are now threatened; more than 40 percent of all the species have suffered significant population declines, and within the past 25 years alone, 122 species have become extinct.
"It's shocking and dismaying," said Wake. "This incredibly rapid increase in the extinction of amphibians around the world is unprecedented in my lifetime."
The class called amphibians includes not only frogs and toads, but also salamanders, newts and the little-known group of legless, worm-like creatures called caecilians. They are extremely ecologically useful because as predators they consume harmful insects by the millions; in the laboratory they are widely used for basic scientific research; their bodies can be harvested for medicines as well as food; and many instances of mass mortality have warned -- like canaries in a coal mine -- of environmental problems in the offing.
Conservation groups in Oregon and Northern California are particularly concerned over the fate of the rare Siskiyou and Scott Bar salamanders. The fungus disease has been found in their habitats, which have also long been threatened by logging in old-growth forests.
The groups filed suit against the U.S. Fish & Wildlife Service in San Francisco federal court Thursday, seeking to compel the agency to begin a "status review" to determine whether the two species need special protection under the Endangered Species Act.
E-mail David Perlman at email@example.com.