How coral reefs might survive climate change

The divers shrieked into their regulators, arms and legs flailing in delight. It was August 2020. Thirteen feet down on a reef in the Florida Keys, marine biologist Hanna Koch and her colleagues from the Mote Marine Laboratory & Aquarium had been hovering, waiting. Just before midnight, in a silent explosion from coral all along the reef, tiny pinkish orange bundles of sperm and eggs began to rise, speckling the sea with a pointillist eruption of life.

The team’s happy dance set off electric blue sparkles from the bioluminescent organisms in the sea around them. “It looked like we’d created our own fireworks,” Koch says. “It was beautiful.”

This sudden flurry is how many reef-building corals typically reproduce—usually once a year on a summer night a few days after a full moon. Cued by the lunar cycle, water temperature, and day length, coral species across Florida’s reefs simultaneously release trillions of sperm and millions of eggs; it’s a frenzy that boosts genetic diversity and ensures some small percentage of eggs will be fertilized, settle onto the reef as larvae, and seed the next generation.