Robert van Woesik, a coral expert at the Florida Institute of Technology, was not involved in the research.
He questions whether conditions in the study accurately reflect those found in nature.
For example, the coral samples were exposed to sunscreen while in plastic bags to avoid contaminating the reefs. But van Woesik worries this prevented dilution of the chemicals through natural water circulation.
"Under normal situations on a coral reef, corals would not be subjected to these high concentrations because of rapid dilution," van Woesik said.
But according to study author Danovaro, the effect is not dose dependent—so coral's exposure to a very small dose of sunscreen is just as dangerous as a high exposure.
"It is more like on-off," he said. "Once the viral epidemic is started, it is not a problem of toxicity."
Rebecca Vega Thurber, a marine virus and coral researcher at San Diego State University in California, said the new results are further evidence of an alarming trend.
"Other [human-induced] factors such as coastal pollution, overfishing, and sedimentation all contribute to coral reef habitat degradation, and this work continues in that vein," said Vega Thurber, who was also not involved in the research.
(Related news: "Coral Reefs Vanishing Faster Than Rain Forests" [August 7, 2007].)
"But before we ban sunscreens, we must first determine if local ambient concentrations of sunscreens are positively correlated with coral bleaching events."
Danovaro says banning sunscreen won't be necessary, and points out two simple things swimmers can do to reduce their impact on coral: Use sunscreens with physical filters, which reflect instead of absorb ultraviolet radiation; and use eco-friendly chemical sunscreens.
Australian researchers are also working to develop a sunscreen based on a natural ultraviolet-blocking compound found in coral.
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