Coral Sex Is Spectacular

Which species will adapt to climate change—and which ones won’t.
Feb. 26 2013 3:02 PM

Swimming in Sperm and Eggs

Coral sex is explosive, exquisitely timed, and funky.

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One after another, the crew members sat on the gunnels, held their masks, and fell backward into the dark water. I splashed in with considerably less grace and followed Brian Nelson of the National Aquarium. Underwater, our lights illuminated schools of tiny, silvery fish and clouds of floating plankton. The water was rough, and I dropped close to a patch of stinging fire coral. I scuttled awkwardly into deeper water.

Sponge coral in Carrie Bow Cay, Belize, during the 2012 spawning season.
Sponge in Carrie Bow Cay, Belize, during the 2012 spawning season

Courtesy of Abby Wood

Nelson shone his light on a broad yellow coral arm, like a doctor examining an especially interesting rash. He looked into the tiny mouths of the coral polyps, trying to spot the pearly-pink egg-sperm bundles as they “set,” or prepared to emerge. He moved on to another coral and then another, finding nothing. The spawn would not happen tonight, at least not on this reef.

Rising to the surface, Nelson spat and shook his head. “There’s a lot of life down there—there’s just a vibe, like something’s going to happen,” he said. “But the more you know about coral, the less …”

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Hagedorn shouted from the boat. “See anything?”

“No.”

“You’re kidding.” Her voice was flat.

Nelson sank underwater again, continuing his search. After another half-hour, we returned to the boat. No one had seen any signs of spawning.

Before climbing the ladder back into the boat, I dropped under the surface for a final look. Two reef squid, each as long as a forearm and nearly transparent, lingered under the hull. They startled and paused, and then one bluff-charged into the beam of my flashlight, its glassy fins flared. I felt taunted.

The next day, everyone was tense, aware that if the spawn didn’t happen that night, it was unlikely to happen at all. They kept up a studied cheerfulness, organizing and re-organizing equipment. The day was hot, humid, and still.

Just after sunset, a light rain began, and wind shook the palm fronds. That was a bad sign, everyone agreed. Or maybe it was a good sign. The aquarists traded stories of successful and unsuccessful spawns, like anxious relatives awaiting a birth.

Carrie Bow Cay, Belize, during the 2012 coral spawning season.
Dr. Nicole Fogarty arranging vials inCarrie Bow Cay, Belize, during the 2012 coral spawning season

Courtesy of Abby Wood

The group gathered on the research-station porch, drumming fingers and jiggling knees. Nelson had turned his baseball cap inside out, rally-cap style. Andrew McLeod, who had a worsening ear infection and a fierce set of mosquito bites, scratched. One of the station researchers had plugged an iPod into a small set of speakers. As the group sat in silence, Johnny Cash began to sing “Flushed Down the Bathroom of Your Love.”  

Departure time arrived, and I followed McLeod into the shallow water just off the southern end of the island, swimming out to a reef thick with elkhorn and staghorn coral. I held a set of nets; if the coral looked set to spawn, I would hand the nets to McLeod to attach.

McLeod slipped under the surface and finned toward his territory. He stopped at the first elkhorn coral, sinking to the bottom for a good look. After a long minute, he gestured for a net. He moved on to the next coral, and gestured again.

A half-hour later, McLeod and the other researchers had tied down almost two-dozen nets, each topped by a clear plastic collecting vial. In the beams of our flashlights, the nets glowed and swayed like ghosts. Fish darted busily among them. McLeod kept swimming, checking exposed branches of coral.

Then he pointed at the end of one vial, where a few tiny red globes hung in the water. I looked at a nearby branch of coral and realized that what I had thought was an especially thick cloud of plankton was, in fact, a cloud of sperm and eggs, each bundle floating out of a coral polyp mouth and rising to the surface.