Coral spawning: Scientists try to capture sperm and eggs of endangered reef species.

Coral Sex Is Spectacular

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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Abruptly, it seemed, we were surrounded by a storm of spawn—below us, beside us, even collecting in swirls on the dark surface above us.

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

Courtesy of Abby Wood

Another diver passed, giving a thumbs-up. I surfaced, leaned back to look at the Milky Way, and realized that the air stank—a dense, salty, unmistakable funk. The aquarists had told me that they could smell coral spawning, but I’d thought they were joking.

Within minutes, each vial was filled with thousands of bundles, each containing both sperm and eggs. McLeod capped one and handed it to me, moving slowly so as not to break up the bundles and start fertilization before the samples reached the laboratory.


As I swam back toward the boat to deliver the vial, my light, which had begun to dim during the excitement of the spawn, failed. I swam the final stretch in the dark, holding the vial in front of me, skirting silhouettes of coral. I was suddenly aware of the silent, hidden nature of the spawn; only artificial light had turned it into a show.

We returned to land and the aquarists set to work, stirring the sperm and eggs in bowls of seawater to encourage fertilization. It was close to midnight, but the aquarists joked with one another as they bounced up and down the stairs. “Look at all those happy scientists!” bellowed Scott Jones, the science coordinator of the station, as he passed the laboratory door on the way to bed.

Hagedorn laughed. “Really, it takes so little to make us happy,” she said. She has recently developed techniques to freeze and store coral sperm and embryonic cells, a bank that could preserve endangered corals’ genetic material long-term. She held up a plastic vial, which contained about a teaspoon of sperm and eggs. “But just think,” she said to no one in particular. “This is enough for an entire reef.”

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

Courtesy of Abby Wood

When the group went to bed, well after midnight, they were still happy. The elkhorn coral eggs had been fertilized, and soon the aquarists would move tens of thousands of coral larvae into incubation tanks of warm, circulating seawater.

In the morning, the news was not so good. A tropical depression was headed straight for Belize. By noon, the depression had become a tropical storm, and the sky was chalk-white and heavy. It was clear that everyone on Carrie Bow would have to evacuate to the mainland.

The larvae couldn’t be moved at this early stage of their development, so the aquarists attached battery-powered pumps to the tanks and left the larvae to ride out the storm alone.

The group spent a night in the mountains near the Guatemalan border, waiting glumly for Harvey to blow over. The younger researchers passed the evening over poker and coconut rum. They finally returned to Carrie Bow the next afternoon, fully expecting the larvae to have suffocated. When they peeked into the tanks, however, they saw that about half the poppy-seed-sized larvae remained pink and healthy.

On the heels of that storm, however, came another, and with it travel delays and confusion. When the aquarists finally arrived home and opened their sealed boxes of coral larvae, they found that the stress of the overnight evacuation or of extended travel had somehow interfered with development. Not one coral larva was still alive.

Heroic measures to save endangered species, it turns out, are just like any other kind of heroism—difficult, often expensive, likely to fail. It’s a lot cheaper and easier to protect animals and plants before they’re in mortal danger, but for many species—including the staghorn and elkhorn corals—that chance is gone. Marine protected areas and other traditional conservation measures may still do some good, but in the long term, their survival may depend on the sperm and eggs in Mary Hagedorn’s freezers, the handful of healthy captive-grown coral colonies in aquaria around the world, and the small crew of people willing to tangle with hurricanes, fate, and epic frustration on the Caribbean reefs.

This summer, the aquarists will try again. If the weather is good and the coral cooperative, they’ll return with hundreds of thousands of coral larvae. And if not … well, they’re trying not to think about that possibility. When it comes to corals, they know they can’t count on much.

Michelle Nijhuis is a contributing writer for Smithsonian, a contributing editor of High Country News, and a 2011 Alicia Patterson Foundation fellow.