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How Scientists Discovered the Link Between Sunscreen and Coral Reef Death


It’s now commonly known that many chemicals commonly found in sunscreen are harmful to coral reefs. But that link wasn’t established until 2015 and many challenges to mitigating the negative effects remain.

It was a local tip that gave Craig Downs his hypothesis. While on a team investigating the death of coral reefs in the U.S. Virgin Islands, a local resident told him that over-tourism was to blame. Specifically, Downs was told that sunscreen was the culprit.

“At the end of the day, when the tourists had left and the water had calmed, you could see the sunscreen sheen on the surface of the water,” Downs recalled.

His team set about to test the hypothesis in the U.S. Virgin Islands and later Hawaii.

Credit Wikipedia Commons
Corals bleach when exposed to environmental stresses like warmer ocean temperatures. Craig Downs' research found that coral colonies can recover from bleaching events if they have good water quality.

They would eventually find that oxybenzone and other chemicals common to sunscreens kill coral larvae. Most corals reproduce sexually, with male and female spawners releasing eggs and sperm into the water to form larvae.

Without those larvae, coral colonies cannot replicate and will eventually die off.

Downs’ discovery has led to the passage of oxybenzone sunscreen bans in Hawaii, Key West, and the Republic of Palau. But he cautions that there are many other threats facing reefs.

“Sunscreen pollution is about one of 100 to 1000 cuts a coral reef can experience, and it’s really location dependent.”

"At the end of the day, when the tourists had left and the water had calmed, you could see the sunscreen sheen on the surface of the water." - Craig Downs

Downs cited excessive sediment and agricultural run off as two of the major threats in Hawaii. Chemical sunscreens can even be problematic when used on land because they can still reach the ocean via the sewer system after urination and showering. Those same chemicals are also found in other cosmetic products.

Sewage outflows have been cited as a major contributor to the decline of coral reefs off the coast of West Maui.

According to Downs, clean water is the most important factor in improving the resiliency of sensitive coral reefs. He said that if a reef is situated in an area with good water quality, they can recover from a bleaching event relatively quickly. In some cases, bleaching events even resulted in higher levels of biodiversity; a process Downs equated to natural forest fires encouraging forest health.

The level of awareness about threats to coral reefs among members of the public and elected officials gives Downs cause for hope.

“Where there is a crisis there is an opportunity. And what I see is an opportunity for universities and companies to find safer sunscreen alternatives.”


Saturday is World Reef Day. Free public events are planned at Waikiki Beach. 

When: Saturday, June 1, 2019, from 7 – 10:30 a.m. Where: Dukes Waikiki, 2335 Kala?kaua Ave. | Public parking available Lyft codes for World Reef Day Waikiki: For New Users: REEFDAY (Up to $20 in credit, $2 off per ride); For Existing Users: REEFDAY19 (10% off to and from event)

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