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Amphibians at risk

By Alok Jha

LONDON, OCT. 15. A third of the world's amphibian species are in danger of extinction, according to a global survey. Scientists think the collapse in numbers might be a warning that the environment may be in a worse state than has been assumed, for amphibians are known to be the most sensitive of all animals to subtle changes in their ecosystems.

There is also a new spectre that has come to haunt the frogs, toads, salamanders and newts that live in and out of water — a fungus that has already destroyed entire populations in many parts of the world. Scientists have known since the 1980s that many amphibian species are vanishing but the scale of decline revealed by the survey, published in Science, has stunned them. Nobody knows what is causing the devastation but it is likely to be loss of habitat to pollution, climate change and increasing competition with humans.

More than 500 scientists from some 60 countries took part in the three-year Global Amphibian Assessment, a study of the world's 5,743 known amphibian species. One in three — a total of 1,856 species altogether — are threatened with extinction, they say. The latest count shows 122 amphibian species have become extinct in the past 20 years. At the global level, scientists say that the drop could be an indicator of the poor state of the environment.

``Amphibians feel the effects of water pollution, climate change before other forms of life including mankind,'' said Neil Cox, a programme officer with the joint World Conservation Union and Conservation International biodiversity assessment unit, which coordinated the survey. ``They are the best indicators overall of environmental health largely because their porous skins allow for water transpiration and movement of chemicals.''

But damage to the environment is not the whole story. Many species have disappeared from pristine habitats that have had little environmental damage. ``This is thought to be a response partly to outbreak of the disease chytridiomycosis,'' Mr. Cox said.

A fungus of the chytrid family called Batrachochytrium dendrobatidis causes the disease. It infests the skin of adult amphibians and the mouthparts of their larvae. ``Amphibians drink through their skin and they also breathe through their skin, so anything that happens to their skin really screws them up,'' said Matthew Fisher, a molecular epidemiologist. ``Tadpoles carry it but they're absolutely healthy. It's when they metamorphose into little froglets that they die instantly — as soon as they hop out of the pond.''

There is no practical treatment for the disease, concentrated in Australia, North and Central America and the Caribbean.

The fungus has been implicated in the extinction of the Kihansi spray toad from Tanzania. In Europe, it has been found infesting the common midwife toad. — © Guardian Newspapers Limited 2004

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