As a team of scientists motor out off Key Biscayne, the evening seems perfect — subtle breeze, balmy water, a ruby sunset cutting through clouds.

It’s also a perfect evening for coral sex: Staghorn coral, the species in question, like to spawn a few days after a full moon in summer, when the water temperature is just right. They might spawn twice a year. Or only once. Or not at all, if they’re stressed out.

These aren’t just any staghorns, though. They’ve been carefully tended to in a nursery by University of Miami researchers, and then planted on the nearshore reef. If they can reproduce, it’s a big deal.

“We hope tonight is the night!” says project co-leader and coral scientist Diego Lirman as his team of biologists prep scuba gear on the stern of the boat.

The stakes are high: Lirman and his team at the university’s Rescue A Reef program and Coral Reef Futures Lab hope to prove that Florida’s coral reefs, which stretch 300 miles, from the Dry Tortugas north to Port Saint Lucie, and which had been decimated by pollution and warming seas, can not only be rebuilt, but can be bred to be more resilient to climate change. In turn, those reefs could protect coastal cities such as Fort Lauderdale.

University of Miami Rosenstiel School of Marine, Atmospheric, and Earth Science associate professor Diego Lirman prepares his dive gear before a night dive to check on coral spawning on Monday, Aug. 15, 2022, in Key Biscayne. A group of students and scientists were hoping to observe the coral spawn and collect their eggs and sperm. The goal is to create new coral that will later be transplanted to help repopulate part of the Florida Reef Tract. (Wilfredo Lee/AP)

Coral, despite their rocky appearance, are animals.

One antler-like staghorn is made up of hundreds of soft interconnected individuals, known as polyps, surrounded by a hard limestone shell that they build from calcium in the water.

If the polyps are indeed in the mood tonight, they’ll release their eggs and sperm by moonlight to mingle on the gentle incoming tide. The researchers will collect some of the genetic stew — they say it looks like Dippin’ Dots ice cream granules — take it back to the lab, and breed them with other staghorn known to be heat-tolerant.

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As the sunset dims, Lirman explains the breeding process.

“We’re gonna do all sorts of fun things with them — cross them with different types of genotypes from this area, different genotypes from the Keys.” They’ll then nurture those coral babies and plant them on the reef again and study their fitness.

“It’s selective breeding. Every new coral baby that we’re able to plant, that’s a new genotype,” Lirman says. “Who knows, maybe those will be the ones that survive bleaching events and acidifications and grow stronger and survive hurricanes. You never know — we might get the next Lionel Messi of the coral world.”

It’s not just biologists on this quest for the coral Messi.

University of Miami's Rosenstiel School of Marine & Atmospheric Science senior research associates Dalton Hesley, left, and Liv Williamson prepare for a night dive to check on coral spawning on Monday in Key Biscayne. (Wilfredo Lee/AP)

The project is funded, in part, by a $7.5 million grant from the Department of Defense, which is looking for ways to enhance coastal resiliency. They want to know if a blend of human infrastructure (artificial reefs engineered to be coral- and biodiversity- friendly) and green infrastructure, such as coral, can protect low-lying cities such as Fort Lauderdale, as well as coastal military bases, from the brutal storms and sea-level rise predicted for the coming decades.

Tonight’s moonlit expedition is a small step in answering those questions.

A mile or so off Key Biscayne, just after sunset, the team locates the dive site.

The UM team has been outplanting nursery-grown corals at local reefs sites since 2017, and first witnessed them spawning in 2020. At this site, they’ve outplanted some 30 to 40 large staghorn, which should be sexually mature by now.

They don their dive gear and hop in. The reef is about 20 feet down, with staghorn and a forest-like mix of other coral giving way to limestone crevasses and crannies. Schools of small fish shimmy this way and that. Snapper lurk in their caves.

The researchers scuba dive down and assess the situation, cracking open some of the staghorn to see if their eggs and sperm are ready to go.

The texture of a staghorn coral preparing to spawn last week. The egg-and-sperm bundled are the spherical objects just inside each coral exterior. Staghorn tend to spawn once or twice a year a few days after a full moon in summer. (Liv Williamson/Courtesy)

Though these staghorn stand like mature oak trees above the other coral, most of them wouldn’t be here were it not for UM’s efforts. Staghorn are listed as threatened under the U.S Endangered Species Act, and their fate is indicative of coral globally.

A 2021 paper published by researchers at the Institute for the Oceans & Fisheries, University of British Columbia, found that living coral coverage around the planet has declined by half since the 1950s. At the same time, the human population, which harvests fish from coral reefs, has increased by 174%.

Climate change has raised water temperatures, leading to coral bleaching, where stressed corals expel symbiotic algae, their main food source, and turn pale or white. The bleaching leads to higher mortality. And in areas such as South Florida, with intense human impact, coral has to tend with stressors such as coastal pollution, nutrient runoff, wastewater runoff and sedimentation, which can smother reefs.

[  Coral protection could have wide-ranging impact ]

A UM study found that the 2012-2016 dredging of Miami’s Government Cut by the Army Corps of Engineers stirred up sediment that buried from 50% to 90% of nearby reefs.

The study estimated that more than 500,000 corals died within 550 yards of the dredge channel, and the dredge may have affected corals as far as 15 miles away.

Two snorkelers follow divers with lights during a night dive to check on coral spawning, Monday, Aug. 15, 2022, in Key Biscayne, Fla. A group of students and scientists from the University of Miami Rosenstiel School of Marine, Atmospheric, and Earth Science were hoping to observe the coral spawn and collect their eggs and sperm, called gametes, to take back to the lab to hopefully fertilize and create new coral that will later be transplanted to help repopulate part of the Florida Reef Tract. (AP Photo/Wilfredo Lee) (Wilfredo Lee/AP)

Reefs such as the Florida Reef, the only barrier reef in the continental U.S., take thousands of years to form.

They protect shorelines, and are home to at least 25% of all marine species, according to the United Nations.

In Florida, that includes juvenile phases of delicious and economically valuable grouper and snapper. They’re also major tourism drivers in Florida, pulling in $1.1 billion annually and supporting 71,000 jobs in South Florida, according to the state’s Department of Environmental Protection.

Back up on deck, senior research associate Liv Williamson, who was leading the action underwater, has a big smile on her face as she takes off her oxygen tanks.

“We cracked a few branches of the staghorn coral and saw that a lot of them are gravid, which means they contain bundles of eggs and sperm ready to go,” she says. “That doesn’t guarantee that they’re going to release those tonight, but they are pregnant, more or less.”

Pregnancy in coral is quite different from pregnancy in humans. Williamson explains that staghorn are hermaphrodites, creating both egg and sperm, but an individual coral’s gametes can’t fertilize one another.

At just the right moment, the colonies, and those around them, synchronize and release their egg/sperm bundles, which float to the surface, like a snow flurry in reverse. There they separate, and mingle with gametes from other colonies, making coral babies that will drift, transform into larvae, and after several days, descend to hopefully attached to a reef.

In this photo provided by the University of Miami's Rosenstiel School of Marine & Atmospheric Science staghorn coral spawns, Sunday, Aug. 14, 2022, near North Key Largo, Fla. (Liv Williamson/University of Miami Rosenstiel School of Marine Atmospheric and Earth Science via AP) (Liv Williamson/AP)

Williamson says the work they’re doing now is a precursor to combining gray (human) and green (natural) infrastructure, as the DOD envisions — planting the coral on special concrete structures.

Key to the project is the fact that staghorn and other branching corals create a three-dimensionally complex barrier that does a good job of breaking up wave energy, according to Williamson.

“Just dumping concrete in the water does work for mitigating wave impact,” adds Lirman. “But the structures look awful. They get overgrown by algae, they don’t get corals. They have very few fish. So the idea is to build a structure that functions as a reef. That’s our challenge.”

Dr. Catherine Campbell of DARPA, the Department of Defense’s research and development agency, says that one of their pillars is to deal with climate change. They’re keen on hybrid gray-green infrastructure for a few reasons.

First, a gray/green reef would dissipate wave energy before it hits the coast.

Secondly, it will create a healthy environment, and thirdly, the reefs could be self-sustaining and self-healing, and not have the repair costs of gray infrastructure.

If Williamson and her team spot the egg/sperm packets poised at the mouth of each coral polyp on the next dive, they’ll put nets over the coral and collect them for the lab’s breeding program.

It’s fully dark, almost 10:30 p.m., the time Williamson says it’s most likely the coral will get frisky. She and her team dive in and swim out 70 yards or so to the site. They search below for signs of procreation, their lights like underwater fireflies with the South Beach skyline in the distance.

A pair of researchers surface. “Dude, I just saw an octopus!” One says. “Bucket list!!” They high-five.

Staghorn coral releasing their egg-and-sperm bundles during a spawning event. (Liv Williamson/Courtesy)

Suddenly the orange moon crests the horizon, a lopsided pumpkin.

Williamson and her team continue to hunt below the surface, moving from staghorn to staghorn, gently shining their lights and examining the branches for any indication of sex.

But there’s no underwater snow flurry, no nets full of Dippin’ Dots. After an hour or so in the water, the divers surface.

No spawn, despite the perfect evening.

“It was a little disappointing,” says Williamson when she surfaces. “But I guess it’s just not their day to give birth. It could happen tomorrow. It could happen the next day.”

As the team bobs in the dark and waits their turn to climb back on board, music starts to pipe through the boat’s sound system.

“Ah, we should have played something romantic,” says one of the researchers.

“Next time I’m bringing some Barry White,” says Williamson.

This story was produced in partnership with the Florida Climate Reporting Network, a multi-newsroom initiative founded by the Miami Herald, the South Florida Sun Sentinel, The Palm Beach Post, the Orlando Sentinel, WLRN Public Media and the Tampa Bay Times.