The world's coral reefs are in crisis. Only 46 percent of reefs around the world are regarded as healthy and not under immediate threat. By the 2050s, over 95 percent of the word's reefs will be under threat, according to the World Resources Institute, a global research institute.
There are many factors that contribute to the poor health of coral reefs, such as pollution, overfishing that upsets the delicate ecological balance of coral systems, and climate change. But coating yourself in sunscreen before snorkelling over a reef is definitely causing more harm than not.
According to new research from an international team of scientists led by Craig Downs of non-profit scientific organisation Haereticus Environmental Laboratory in Virginia, a common UV-filtering organic compound used in sunscreen is toxic to coral.
Oxybenzone kills living coral, the team found, but its effect on the invertebrates doesn't stop there: It also causes DNA damage in adult coral, and deforms the DNA in larval coral, which means the larval coral's chances of developing properly are low.
The team sampled waters around coral reefs in Hawaii, the US Virgin Islands and Eilat, Israel. They found oxybenzone in the highest concentrations in the water in locations popular with tourists.
"The use of oxybenzone-containing products needs to be seriously deliberated in islands and areas where coral reef conservation is a critical issue," Downs said.
"We have lost at least 80 percent of the coral reefs in the Caribbean. Any small effort to reduce oxybenzone pollution could mean that a coral reef survives a long, hot summer, or that a degraded area recovers. Everyone wants to build coral nurseries for reef restoration, but this will achieve little if the factors that originally killed off the reef remain or intensify in the environment."
To gauge the effect of oxybenzone on coral, the team exposed both adult and larval coral to increasing concentrations of the compound. Cells from seven different species of coral, three of which are currently listed as threatened under the US Endangered Species Act, were killed when exposed to oxybenzone levels similar to levels found in ocean water samples.
The team also found that the oxybenzone hindered larval coral growth by trapping them inside their exoskeleton. This prevents them from being able to float and drift to new places to form new coral colonies.
Finally, the oxybenzone was found to contribute to coral bleaching, the phenomenon whereby the algae-like protozoan symbionts that usually live inside coral are lost, which in turn causes a loss of pigmentation. Bleached coral are not dead coral, but they cannot grow as normal until the protozoa return.
When collecting water samples, the team conducted their dives without wearing sunscreen. Their alternative sun-protection methods could be used by tourists, explained John Fauth, a University of Central Florida professor who contributed to the research.
"Wear rash guards or scuba wetsuits and skip all the hygienic products when you go diving," he said. "If we could do it for a week at a time, people can certainly forgo it for a few hours to help protect these reefs for our children and their children to see."