MONTEVERDE, Costa Rica — Biologists living in the misty cloud forest high up in the Monteverde mountains of Costa Rica fear that the celebrated Golden Toad, a small, brilliant orange amphibian found only in one square mile of this region, is on the verge of becoming extinct.
While scientists heatedly debate theories about global warming, the disappearance of species like the Golden Toad in remote mountain habitats offers important confirmation that global climatic change is indeed taking place. "It isn't as if we were talking about a problem caused by a dam project, or pollution from a nearby factory," said Gary Diller, an American biologist who has lived at Monteverde for 20 years.
The reason for the Golden Toad's disappearance, Diller and others believe, is increasing levels of ultraviolet radiation entering the Earth's atmosphere due to ozone depletion. "Amphibians are highly susceptible to ultraviolet radiation," Diller reports. "The ozone hole is, perhaps, the key reason why the Golden Toad has not been seen since 1987."
The effects of increased ultraviolet radiation on tropical environments are unknown. What has been documented, however, is that exposure to higher levels of ultraviolet radiation in temperate zone climates results in increased skin cancer and eye damage in humans and decreased agricultural production. Biologists speculate that these effects are magnified in areas lying closer to the Equator, which are already exposed to higher levels of ultraviolet radiation than more temperate areas.
Biologists at Monteverde are anxiously monitoring the 1990 breeding season to see if any Golden Toads return to their breeding pools. Jerry James, who discovered and provided the first scientific description of the Golden Toad in 1963, recently visited the reserve to confer with colleagues about its fate. "I am at a loss to explain its disappearance," James said. "I can only hope that the frogs return to their mist pools this year."
The plight of the Golden Toad is shared by other amphibians in the Monteverde cloud forest. The Harlequin frog and the glass frog, which live within a few miles of the Golden Toad, have also disappeared in recent years. The Dink frog suffered a significant drop in its population about two years ago, Diller reports, but its number has risen during the last two breeding seasons. Diller speculates that the Dink frog's darker skin may provide it with stronger protection against the effects of ultraviolet radiation than the Golden Toad.
Diller, as well as other naturalists living in the reserve, cite altered weather patterns at Monteverde as another possible factor behind the decimation of the amphibian populations. "Since 1987, the rainy season comes later and is shorter," notes Michael Fogden, a naturalist photographer who lives on the outskirts of the reserve.
"The mist pools are high and dry. This cuts precious time for the breeding cycle of most frogs," Diller states. "The Golden Toad cannot miss too many breeding seasons. If it doesn't return this year, then it is almost certain to become extinct in its natural habitat."
The fate of the Golden Toad is not without irony, say environmentalists. It suggests that mankind may have waited too long to move on environmental issues. Even when natural habitats are set aside to be protected and offer refuge to endangered species, other factors, such as the ozone and global warming, may render these parks useless.
"This is happening all over Latin America," laments Jorge Canto, who has been active in establishing rain forest reserves in Mexico's Yucatan peninsula. "What's the point of establishing a biosphere reserve like Sian Ka'an which encompasses 1.3 million acres if acid rain will pour down everywhere, poisoning the park?"
"Frogs are important because they are the first to die when dramatic changes in the environment occur," Canto adds. "If the Golden Toad becomes extinct, even when everything humanly possible to protect its environment has been done, it does not bode well for environmental efforts."
Adds Diller: "How can you protect the Earth if the ozone is destroyed? If the frogs go, we follow."