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Ecotoxicologist Craig Downs describes his main work goal as “preventing zombies”—communities of coral or other marine creatures that appear to be thriving, but upon closer inspection, turn out to be composed only of adults lacking the ability to reproduce. These populations are like the “ living dead ,” a generation away from vanishing, according to scientists who discovered them in dying reefs across the Caribbean in 2016.

Globally, coral reefs are in decline for a number of reasons , including climate change, coastal development, and pollution. Over the years, Downs, executive director of Haereticus Environmental Laboratory in Virginia, has studied sunscreen, microplastics, and most recently, beach showers, in an effort to understand the effects of these human-made substances on some of the world's most popular vacation destinations. His latest study , published in July, could also breathe new life into an old law.

In April, the Clean Water Act , the keystone US law on water pollution, took what many environmentalists describe as a tough hit. In a controversial shadow docket decision , the Supreme Court voted to remove states’ power to block federally approved, but environmentally damaging, projects. Commentators decried the attempt to strip states of the right to protect their own waters, one of the core principles enshrined in the act.

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Medical authorities have spent years convincing people to use sunscreen to limit their exposure to UV light. But that effort has had a bit of a setback, as several locations have recently banned the use of sunblocks by beachgoers. Those bans took effect after local waters were found to have high levels of some of the chemicals in sunblock, which was associated with the lower health of nearby coral reefs.

Several studies have indicated that one specific sunblock component, a chemical called oxybenzone, is at the root of the problem. But the mechanism by which oxybenzone could harm corals wasn't clear. And, without that understanding, it's difficult to tell which sunblocks might pose a risk.

Now, researchers from Stanford University have identified the problem. The corals convert oxybenzone from a chemical that can harmlessly absorb UV light to one that damages biological molecules after being exposed to UV. And there's evidence that coral bleaching makes matters worse, as the coral is less able to withstand exposure.