The Deadly Plight of the Disappearing Frogs

Frogs and their relatives have existed on Earth since the dinosaurs, for more than 360 million years. But now their continued existence is seriously threatened by a deadly fungus called chytridiomycosis. Scientists believe that the fungus originated with African clawed frogs decades ago. These frogs are not affected by the fungus, but they carry it on their skin. Scientists around the world have used these frogs for research, and from the 1930s to the 1950s, the frogs were used to conduct pregnancy tests. And people have also kept the frogs as pets. As a result, African clawed frogs have spread far beyond their native habitat, carrying the fungus with them.

Researchers suspect that the fungus isn’t just riding on the backs of one species of frogs today, though—they think it may now be spreading through airborne spores to reach other types of frogs who not immune to it like the African clawed frogs are. The fungus attacks the parts of a frog’s skin that have keratin, a substance that makes the skin tough and sturdy. Since frogs use their skin in respiration, the effects of the fungus make it difficult for the frog to breathe. The illness also damages the nervous system, affecting the frog’s behavior.

Cytrid fungus is probably transferred by direct contact between frogs and tadpoles, through infected water. Tadpoles are not affected by the fungus because they have only a small amount of keratin around their mouths. But as frogs grow, their skin thickens on the parts of their bodies that come into contact with the ground, such as the abdomen and the soles of their feet. So although the fungus doesn’t usually bother tadpoles, it can kill adult frogs. The disease may not kill frogs immediately, and as a result they can swim or hop to other areas before they die, thereby spreading fungal spores to new ponds and streams.

Experts believe that as many as one-third to one-hald of the planet’s 6,000 amphibians are in danger of disappearing—which would be one of the worst mass extinctions since the age of the dinosaurs. A film produced by Discovery Studios, The Vanishing Frog, hopes to focus worldwide attention on the deadly fungus that is destroying frogs and other amphibians. The film features Animal Planet’s Jeff Corwin on a worldwide mission to provide viewers with some of the causes that may be contributing to the plight of the frogs.

"Frogs are incredibly amazing creatures with a variety of astonishing skills and innate abilities," commented Corwin. "The plight of the small amphibians is—unfortunately—quite large. Frogs have been with us since the dinosaurs; they are a critical part of the ecosystem and now they are disappearing." The film is sponsored by Animal Planet and the Clorox Company, whose bleach is being used in the field every day in the battle to save the frogs.

The battle is not a small one, and it has proven to be impossible to contain. As an example, scientists have measured Bob’s robber frog populations at three tropical streams in Panama since 1999. The frog is already an endangered species, but the amphibians were abundant in the three protected sites where scientists were keeping track of populations. Along a 200-meter path, researchers counted anywhere from 19 to 68 frogs among the creek boulders in the rainforest streams, until late September 2004. That’s when scientists discovered four dead frogs—and that’s when they discovered the cytrid fungus. Within two months, all robber frogs at the three streams were gone. And there is little likelihood that the frogs will return, since all the water is now infested with the fungus. Since then, researchers all around the world have begun to discover the fungus in numerous different species of frogs, and it is spreading at an alarming rate.

Although the problem of the vanishing frogs may appear to be something only researchers can solve, there are things that the public can do to help contain the spread of the fungus. The first thing is to report the appearance of sick frogs or frogs that seem to have died without an obvious cause to your local authorities. A sick frog may have discolored skin, have peeling of the skin, be sluggish and unresponsive, and may sit out in the open without protecting itself, or spread its legs slightly away from its body, rather than keeping its legs tucked in close to its body.

Wet or muddy boots and tires, fishing, camping, gardening, or boating equipment may also be contributing to the spread of the disease. And never, ever release pet frogs into the wild. Released pet frogs can breed, overwhelming the local frog population, and they can spread disease.

For more information about the chytrid fungus and efforts being made to combat it and protect frogs, visit the Amphibian Ark (http://www.amphibianark.org/chytrid.htm).