Climate Change Linked to Amphibian Deaths.

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Toad embryos in the Cascade Range of Oregon appear to be dying due to a chain of events that ultimately is linked to climate change, demonstrating both the importance of large-scale global trends and the complexity of their impact on individual species. A study by scientists from Oregon State University, Corvallis, and Pennsylvania State University, University Park, traces one link to another in a pattern that begins in the southern Pacific Ocean and ultimately results in masses of dead, rotting toad eggs in a small alpine lake thousands of miles away. These are signs of an amphibian species that is in decline.

"This study suggests a causal explanation for problems with one amphibian species in the mountains of Oregon," emphasizes Andrew Blaustein, a professor of zoology at Oregon State University. "But in a larger sense it shows that if we want to understand the complex ecology of the world around us, we must start looking at the big picture. There will not be simple or easy answers for all of our problems."

Blaustein co-authored the study with Lisa Belden of OSU and Joe Kiesecker, a professor of biology at Penn State. For years, these scientists have studied the level of amphibian declines around the world and those of the Pacific Northwest in particular. Among other findings, they have linked amphibian declines in Oregon to elevated levels of exposure to UV-B radiation in sunlight, as well as to infection of embryos by a fungus, Saprolegnia ferax.

They cite evidence that greenhouse warming and other climate changes might be increasing the frequency and intensity of El Nino events, an unusual warming and ocean circulation pattern of the southern and equatorial Pacific Ocean. Other studies have shown clear connections between El Nino events and reduced precipitation in the Pacific Northwest during the winter, when that region gets most of its rain or snow.

"At this point, we looked at the effect of low precipitation on water depth in the Cascade lakes and the amphibians that live in them," Blaustein explains. "We've known for some time that elevated levels of UV-B radiation can cause stress and higher levels of mortality to embryos of the western toad and some other species. Egg mortality has approached 100% in some recent years."

At first, the...