Is Sunscreen from Snorkelers Killing Coral Reefs?

Even if you're careful not to touch coral reefs when snorkeling, just your presence in the water near them might be damaging to the ecosystem—at least, that's what many resorts would have you believe.

Tourists traveling to visit certain coral reefs are often requested or required to swap out their regular sunscreen for a biodegradable alternative if they want to get in the water, for example. In Mexico, at private parks like Xcaret and Xel Ha, or certain public areas like Cozumel's National Marine Park, biodegradable sunscreen has been a standard requirement for years. Some tourism companies even make money off of selling unprepared tourists so-called "reef safe" sunscreen. But is this precaution based on science or is it just a cash grab?

There is some science behind this practice; a 2008 study published in Environmental Health Perspectives found that the chemical compounds in sunscreens trigger a latent viral infection that kills off the symbiotic algae that live on coral. This causes the coral to turn white and eventually die in a process referred to as "bleaching."

But that lone study seems to be the sole evidence that regular sunscreen causes any damage to coral reefs. No one has published a study in the seven years since that has replicated or supported these findings. That's not to say the study's findings aren't legit, but it's a sign that maybe there are more substantial human impacts on coral reefs.

"It's not that sunscreens don't affect coral, it's that there's only been one study on it," said Andrew Baker, a marine biologist at the University of Miami who studies the effects of climate change on coral reefs. "Before we go crazy and pat ourselves on the back for changing to different sunscreens and then feeling that we're saving the reefs, we probably should be looking at these other impacts that are having much greater effects."

So, should we bother with biodegradable sunblock? Baker says it can't hurt, as long as people are taking the time to think about the bigger impacts humans are having on coral reefs. Rebecca Vega Thurber, a microbiologist at Oregon State University who studies coral diseases, agreed.

"The field has shown that habitat destruction, overfishing, and nutrient pollution—not to mention climate change—are likely much more important than single source inputs like sunscreens from tourists," Vega Thurber told me via email. "Clearly anything we can do to reduce the input of foreign substances in the ocean is probably a good thing, but we should pick our battles based on clear data and the efficacy of the mitigation."

What can we do besides changing our sunblock? Baker suggested doing some research on sustainable fishing: a lot of tourists snorkel carefully through a reef during the day and then unwittingly sit down to a seafood dinner that has depleted the reef of important organisms, like red snapper or grouper. He also said you should read up on the tour company you're traveling with, whether it be a resort of a cruise ship, to make sure it properly manages its wastewater and isn't polluting the reef.

But even traveling to these areas in the first place may be a step too far. Jean-Michel Cousteau, son of the famed oceanographer, and founder of the conservation group Ocean Futures Society, has advocated for the use of biodegradable sunblock in the past. But in a statement emailed to me, Cousteau noted that the biggest risks to coral reefs are "pollution runoff and coastal habitat development" as well as climate change. Between the fuel burned up hopping a jet to Mexico, and the encroachment of some of the resorts and tourists spots along the shore, the damage from going on the vacation in the first place will be much greater than the damage from a little sunscreen.

But Cousteau doesn't necessarily have a grim outlook.

"Everything is connected. The discussion on environmentally safe sunscreen can promote conversations about greater threats facing the environment, leading to more awareness and innovative solutions," Cousteau wrote. "The challenges here are greater, but still achievable: lessening carbon pollution, running our societies on renewable energy, and keeping the oceans healthy and clean so that corals may have a chance at adapting to these changing conditions."

The verdict? Sure, swap to environmentally-friendly sunblock if you want. But don't convince yourself it's the cure-all to the real risks facing coral.

Hell or Salt Water is a series on Motherboard about exploring and preserving our oceans. Follow along here.