Can these corals take the heat?

“Like a healthy reef is just this gorgeous ecosystem full of strange beautiful creatures,” says Benji Jones, a Vox reporter who has been covering coral for years. But the world has lost half its live corals since the 1950s. When Jones went snorkeling in Palau, an island nation in the Pacific, he put his mask on and felt like he was “seeing color for the first time.” The reefs there are that vivid. But he wasn’t just there to marvel. He was there to report on a scientist trying to solve a brutal problem: if you plant coral to restore a dying reef, and then another heat wave hits, all that work can vanish in days.

Coral is an animal — a colony of tiny, genetically identical polyps that look like little sacks with tentacles. Each polyp has a partnership with a type of algae that lives inside its tissue. The algae photosynthesizes like a plant and hands off sugar to the coral; in return, it gets a place to live near the sun. When the ocean gets too hot, that partnership breaks down. Scientists think the algae starts secreting something toxic, so the coral ejects it. That’s bleaching: the coral turns white, starves, and will die if temperatures don’t drop. Climate change is the leading threat — a 2018 report estimated that with 1.5°C of warming, we could lose 70 to 90% of coral reefs.