Swimmers' sunscreen killing off coral

From an article for National Geographic News by Ker Than:

The sunscreen that you dutifully slather on before a swim on the beach may be protecting your body—but a new study finds that the chemicals are also killing coral reefs worldwide.

Four commonly found sunscreen ingredients can awaken dormant viruses in the symbiotic algae called zooxanthellae that live inside reef-building coral species.

The chemicals cause the viruses to replicate until their algae hosts explode, spilling viruses into the surrounding seawater, where they can infect neighboring coral communities.

Zooxanthellae provide coral with food energy through photosynthesis and contribute to the organisms' vibrant color. Without them, the coral "bleaches"—turns white—and dies.

"The algae that live in the coral tissue and feed these animals explode or are just released by the tissue, thus leaving naked the skeleton of the coral," said study leader Roberto Danovaro of the Polytechnic University of Marche in Italy.

The researchers estimate that 4,000 to 6,000 metric tons of sunscreen wash off swimmers annually in oceans worldwide, and that up to 10 percent of coral reefs are threatened by sunscreen-induced bleaching.

The study appeared online in the journal Environmental Health Perspectives.