June 20 (UPI) -- When marine biologist Craig Downs first visited the turquoise-blue waters of Trunk Bay in the Virgin Islands National Park in St. John in 2005, he arrived on a crucial mission: Find out why the health of the park's coral reefs was declining.

Downs, part of a team of experts from the National Oceanic and Atmospheric Administration, the University of Central Florida and the University of Hawaii, noticed the absence of young corals in St. John, which was visited by as many as 5,000 people daily at the time. Nearly all the corals were mature, and those injured by tourists or storms were not healing years later. Yet Downs, executive director of the nonprofit Haereticus Environmental Laboratory in Clifford, Va., and his fellow scientists could not find a reason for the coral's decline. The usual culprits in nearby regions of the Caribbean – algae, sewage and agricultural runoff – were not present in Trunk Bay.


It was a mystery until a local man overheard the researchers discussing their frustrations while shopping at a St. John grocery store. "The tourists, mon!" the local exclaimed. He told the scientists that they should visit Trunk Bay and examine the water in the late afternoon after tourists had left the beach. When they visited the bay the following evening, Downs and his colleagues saw "a spectacular iridescent sheen," he said. They tested the bay's water and found that the rainbow slick was sunscreen that had washed off tourists' bodies and into the water.


It contained high amounts of a widely used ingredient called oxybenzone, which Downs and other researchers proved is extremely toxic to corals in laboratory research published in 2015 in the journal Archives of Environmental Toxicology. He said oxybenzone and other chemicals pose the third-biggest threat to coral reefs, after climate change and nutrient pollution from sewage discharge and fertilizer runoff, which causes oxygen depletion. Globally, between 6,000 and 14,000 tons of sunscreen wash off people and into reef areas each year, according to Downs.

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The findings have taken on a new gravity with the unprecedented back-to-back coral-bleaching events of 2016-17 that have devastated two-thirds of the Great Barrier Reef and raised new concerns about the survival of coral reefs worldwide as ocean temperatures continue to rise. Some scientists have called the research inconclusive, as they have not been tested beyond the laboratory. Nevertheless, there's a small but growing movement around the world to ban sunscreens containing oxybenzone from reef areas.

Downs is leading a team of researchers from government agencies, nonprofits and universities studying sunscreen chemical levels in marine mammal tissue, in fish sold to restaurants and in swimming pools. As part of its research, to be published in late 2017, the team has also measured sunscreen chemicals in the fish, water and sand around the Florida Keys, Hawaiian Islands, the U.S. Virgin Islands and several Caribbean countries. New findings include the discovery of aerosol sunscreen on beach sand, which ends up in the ocean during high tide and poses a threat to nesting and baby sea turtles, as well as spawning reef species, such as corals, sea urchins and starfish.


Scientists believe oxybenzone exacerbates the impact of bleaching by undermining corals' resilience to adverse climatic conditions and disease. Most significant, perhaps, is the researchers' discovery that repeated exposure to this common sunscreen chemical alters coral DNA, resulting in a deadly mutation where corals' skeletons grow outside their bodies – encasing them in a tomb in which they're unable to survive.

Oxybenzone harms corals in four ways: It causes young and adult corals to bleach – or lose the living photosynthetic organism that feeds them – when exposed to natural stressors such as heat, cold, lack of light and lack of salt. It also damages coral DNA, which can reduce coral's lifespan and immunity to disease, as well as disrupting normal development and reproduction. Oxybenzone causes deformities in coral larvae that ultimately kill them. Most alarmingly, the chemical is an endocrine disruptor in coral larvae that causes the corals' outer skin cells to turn into bone.

"We knew oxybenzone was a sexual endocrine disruptor from the science of it on fish and mammals, but the skeleton disruption in corals was completely unexpected – and very expensive," said Downs, referring to the fact that he had inadvertently ruined a very expensive piece of lab equipment – simply because he did not expect coral to have been covered by bone.

It turns out that coral larvae skeletons were damaging the electron microscope's diamond-edge knife. "I had to buy them a new diamond knife," Downs said.

Coral reef scientist William Precht saw firsthand the coral-killing effects of oxybenzone on a reef in Panama in January 2016. Precht, a professor of marine biology at Northeastern University, took a dive with his students on a remote reef not visited by tourists. When reviewing the photos of one dive, Precht and his students noticed a brain coral with a perfect handprint of dead tissue. The next day, Precht said a woman in his class admitted to him she had inadvertently touched the reef during a dive two weeks earlier and that prior to the dive she had applied sunscreen to her body with her hands.


The biggest threat to reefs, according to Downs, is rising ocean temperatures due to climate change. The second-biggest threat is pollution from sewage and agricultural fertilizers, which deposits large amounts of nutrients into the water, causing algal blooms that suffocate corals. Downs said he would rank oxybenzone and other chemicals, such as pesticides and toxins leaching from plastic pollution, as the third-biggest threat to coral reef health globally. The fourth-largest threat, he said, is sedimentation from disturbed land, which can bury reefs.

NOAA lists climate change as the top danger to reefs. Higher water temperatures caused by a warming climate can trigger coral-disease outbreaks and coral-bleaching events that have devastated the Great Barrier Reef and other reefs around the world. As the ocean absorbs more carbon dioxide from the burning of fossil fuels, the water acidifies, further damaging reefs. Lastly, climate-change-driven alterations in the frequency and intensity of tropical storms, as well as changes in ocean circulation patterns, can undermine reef health.

While several global coral-bleaching events have struck reefs across the world since 2014, reefs in the Caribbean have been hard hit by bleaching since 2005. In fact, the 2005 Caribbean bleaching event, which killed off half the region's reefs, was the reason Downs was called to Trunk Bay. Downs said sunscreen likely made the reefs more susceptible to the effects of climate change.

There is now a movement to ban oxybenzone-containing sunscreens due to its potential to harm corals – and the local economies dependent on reef-based tourism. Mexico has banned the sunscreen in nature reserves, while the South Pacific nation of Palau prohibits people wearing sunscreen to enter Jellyfish Lake. Hawaii state Sen. Will Espero this year introduced a bill to ban the sale of sunscreen containing oxybenzone. The bill did not pass, but Espero plans to re-introduce the legislation in 2018.


Oxybenzone is also potentially dangerous to humans. The chemical is readily absorbed by the skin and can cause hormone problems and cellular mutations, according to research by the Environmental Working Group. About 97 percent of the United States population has been exposed to oxybenzone, which remains in the environment months after it's introduced as people apply and reapply sunscreen continuously in sunny destinations.

Cheryl Woodley, a coral expert at NOAA's National Centers for Coastal Ocean Science, said people can avoid harming reefs – and themselves – by simply avoiding sunscreens that contain oxybenzone.

"Check labels on sunscreen products for safer ingredients such as non-nanosized titanium oxide or zinc oxide, which are natural mineral ingredients, or wear hats, sunglasses and light, long-sleeved clothing to protect you," Woodley said. "In the water, a long-sleeved shirt or rash guard will help prevent sunburn."

Erica Cirino is a freelance science writer based in New York. This article originally appeared on Oceans Deeply, and you can find the original here. For important news about ocean health, you can sign up to the Oceans Deeply email list.