Amphibian Declines Signal ECOSYSTEM THREATS.

• Position: Brief Article

ZOOLOGY

People who are looking for a single answer that will explain all of the amphibian deaths and declines around the globe are going to be disappointed, maintains Andrew Blaustein, professor of zoology, Oregon State University, Corvallis. It is now a certainty that there are multiple causes contributing to this situation. Nevertheless, the lack of a single, definite cause does not diminish the seriousness of this alarming ecological phenomenon, he says.

"At this point, we can say for sure that there are several causes of amphibian declines, which include rising levels of UV-B radiation in sunlight, pathogens, pollutants, habitat destruction, introduced predators, and, most recently, crop fertilizers. But 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. And some of the things that are killing frogs almost certainly have implications for other animal species, including humans."

The multiple causes of amphibian declines, in fact, help to illustrate how ecological changes may have a synergistic effect to compound problems. In various instances, it might be that UV-B radiation, pathogens, or high nitrate levels by themselves would not be enough to cause death or deformity. Put them all together, though, and you have far more serious impacts. For example, 14 species of amphibians have disappeared from Australia in recent years and five species of amphibians in the Pacific Northwest of the U.S. are listed as candidates for the endangered species list. Others include extinction of the golden toad in Costa Rica, massive egg mortalities of the Cascades frog in Oregon, and amphibian declines in Europe, South America, Asia, and Africa. "This is an incredibly complex problem, a disturbing one, and there's no end in sight," Blaustein predicts.

In 1997, Btaustein published a paper which linked ambient, but rising, levels of UV-B radiation in sunlight to physical deformities in amphibians. This study found that more than 90% of the salamander embryos not shielded from such radiation either died or hatched with deformities, whereas practically all of those protected by special filters survived and were perfectly normal.

In 1998, he co-authored a study which correlated an increase in UV-B radiation to retinal damage in the Cascades frog. It pointed out that the effect of solar UV radiation on the eye and retina are well known in animals and that the risk...