Ultraviolet Radiation Not at Fault for Amphibian Decline

First posted on 05-25-2010

Amphibians are dying off around the world. Scientists are unsure what’s causing the decline in frogs, salamanders and toads, but they are at least beginning to eliminate possibilities and may soon discover the root issue.

Wendy Palen, a Simon Frazier University ecologist, says it is not increasing UV radiation that is at fault. Palen conducted research while working on her PhD from the University of Washington along with Daniel Schindler, a professor of aquatic and fishery sciences at the University of Washington.

Palen and Schindler discovered that UV-sensitive amphibians chose shady or murky water locations to lay their eggs. These spots receive far less UV radiation than full or partial sun sites.

Palen pointed out that, “These findings don’t contest hundreds of studies demonstrating the harmful effects of UV radiation for many organisms, including humans. Rather, it points out the need to understand where and when it is harmful.”

In the late 1990s and the early 2000s, scientists were alarmed about amphibian declines and felt that UV exposure was the root cause. They based their research on limited field studies and laboratory experiments that included a large number of species particularly sensitive to UV radiation.

Unfortunately, those experiments did not consider the “real world” habitats actually encountered by amphibians. Palen and Schindler studied a much larger number of breeding sites, 22 in all.

“When simple tests of species physiology are interpreted outside of the animal’s natural environment, we often come to the wrong conclusions,” Palen said.

In the field, where Palen and Schindler conducted their research, natural sunscreens are present in the form of dissolved organic material floating or suspended in water. The more decaying leaves, grasses and other material present, the less UV exposure to amphibians.

“There hasn’t been a lot of work on whether organisms are capable of sensing UV intensity, but these salamanders certainly do,” Schindler says. “They change their behavior, with the females laying their eggs in the shade when the clarity of the water puts their eggs at risk.”

Amphibians play a vital role as consumers and as food supplies in forests and wetland areas worldwide, including the Ozarks. Their decline in recent years has scientists concerned and scrambling to find an answer. A significantly depressed presence of amphibians could cause major shifts in the ecological balance across large regions of the world.

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