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Nature Watch: Everything from Armadillos to Zebra Butterflies

In the Dark

Life as a frog is not to be envied these days. In addition to the traditional challenges — the natural predators, science teachers, and French chefs— a frog now must contend with deadly fungi, toxic pond water, opportunistic parasites, and genetic mutations of mysterious source.

It's been more than a decade since herpetologists in the United States, Australia, and Central America first noted the localized extinction of frog, toad, and salamander species and an abnormally high level of genetic deformities in certain amphibian groups. Since then causes have been sought, conferences held, and conclusions proposed, but the situation seems only to be worsening. In fact, amphibian extinction and rapid population declines have been observed even in relatively pristine wilderness areas like Yosemite National Park, where seven frog species are in steep decline and three have disappeared completely.

Pollutants, of course, are a prime suspect. Since all frogs at least partially breath through their moist permeable skin, they're extremely sensitive to degraded air and water. As one study demonstrated, half the tadpoles in a body of water with nitrate levels considered safe for human consumption will die within two weeks.

In addition to chemical causes, scientists have recently identified a new fungus, Chytrid, that may play a primary role in these massive frog die-offs. It's believed that the frogs infected with Chytrid suffocate when the fungus coats their skin. Unfortunately, scientists cannot explain why the fungus-induced mortality has appeared simultaneously in several isolated habitats around the globe.

As for the high incidence of extra legs, missing eyes, and misarranged body parts in frogs, one possible culprit may be the increased levels of ultraviolet radiation in recent years due to atmospheric ozone depletion. Frogs in their tadpole stage are especially susceptible to genetic damage prior to their final metamorphosis.

Malformed frogs may also result from parasitic infestation of tadpoles by tiny flatworms known as trematodes. While not a new agent, trematodes may be more prevalent due to expanding populations of host animals such as aquatic snails, which in turn thrive because of heavy fertilizer application near waterways.

And if frogs didn't have enough problems already, introduced cannibalistic cousins like the Bullfrog from the eastern and central United States now dominate western ponds, decimating other smaller frog species.

Whether the current amphibian tailspin is due to chemical pollution, ozone depletion, burgeoning parasites, failing habitats, genetic damage, a new breed of fungi, or the synergistic combinations of several of these factors, we have reason to be concerned. That's because frogs, like the canaries once used in coal mines, are sentinel species that can warn us about environmental stressors that ultimately could prove harmful to humans.

Frog conservation measures start at home. Reducing or eliminating pesticide use is one effective step, since homeowners apply ten times more pesticide and herbicide per acre than farmers. Composting to reduce or eliminate fertilizer applications is also advised, and every effort to protect wetlands, even the smallest seeps, pools, and marshes, provides necessary frog habitat. Finally, children — and adults, too — must learn to leave amphibians in their natural habitats.