As one of the early pioneers for building coral nurseries to save Florida’s imperiled reef, Ken Nedimyer amassed an impressive collection of native elkhorn coral over the years.
While waters warmed and reefs got battered with disease and more frequent episodes of lethal bleaching, Nedimyer fastidiously tended to his Reef Renewal nursery off Tavernier.
Amid worsening conditions fueled by climate change,
Nedimyer carefully catalogued the responses from what he calls his Founders elkhorn. Some faltered, but many thrived, growing to table-sized bundles of branching antlers weighing more than 25 pounds. With 140 colonies housed in his nursery, his elkhorn now outnumber what remains on the reef.
So this past month when they spawned, scientists from around the state raced to construct a makeshift maternity ward. If Florida’s reef ever needed a lifeline, this was it.
READ MORE: Florida promised to restore a quarter of the state's reef by 2050. So where's the funding?
For 12 straight days, teams worked around the clock to deliver coral babies. Altogether, they created more than 60,000 new embryos cross bred with more heat tolerant elkhorn from around the Caribbean. The hope? Rebuild the stony brambles that for thousands of years sheltered fish, lobster, worms, snails and other wildlife and provided a rampart for hundreds of miles of Florida coast from pounding storm waves.
The embryos are now being tended to at labs around the state in what the Florida Aquarium described as the state’s largest conservation effort yet.
”We kind of realized as a group that what Ken had at Reef Renewal was truly unique with that many spawning-sized coral,” said Maren Stickley, a fifth-year Ph.D. student at the University of Miami Rosenstiel School who helped organize the effort. “It’s really an amazing feat.”
If Florida’s reef is to survive long enough to wait out solutions to climate change, this new strategy may be the best hope.
When scientists began to realize reefs might be doomed as oceans grew hotter and hotter, rescue efforts centered on building artificial reefs, mostly by scuttling old ships.
“Ecological recovery of the damaged communities relied on a ‘build it and they will come,’ philosophy based on potential natural recruitment,” UM professor Diego Lirman wrote in a 2016 study.
But that kind of fix can take years to accomplish or attract the wrong kind of weedy corals usually degraded reefs, he warned. It also failed to address endangered coral. Instead, Lirman and others suggested trying ‘coral gardening.’ The relatively new strategy borrowed from forest managers by taking coral cuttings from the reef and regrowing them in nearby nurseries.
“You can go to Home Depot to get everything you need,” he said in 2017.
Up and down the Keys, coral nurseries sprouted, creating a kind of coral pipeline to restock the reef. But ongoing bleaching events made it clear just propagating existing coral would not save the reef. To survive, the reef needed stronger coral. So scientists pivoted to genetics. Nedimyer was part of a team around 2010 that had already started trying to breed coral. But rather than just breed and grow coral, what if they untangled coral’s genetic traits and either found native coral that seemed to survive hotter water and bleaching events or cross bred them with coral from places regularly exposed to higher temperatures.
That led to a two-track strategy: while nurseries continued to grow and replant coral to keep pace with the high demand from the struggling reef, scientists started tinkering in labs at the Florida Aquarium, the University of Miami, the Smithsonian, Mote Marine Lab and other places, figuring out how to make coral artificially spawn in tanks so they could cross breed them.
By 2020, Florida Aquarium scientist Keri O’Neil had succeeded in breeding coral in the lab. In 2022, UM’s Rosenstiel professor Andrew Baker had secured approval to begin importing Caribbean coral that grows in hotter water.
They were just getting started when 2023 delivered a brutal summer ocean heat wave. As temperatures climbed and stayed high for weeks, nearly all the remaining wild elkhorn on the reef died.
”After 2023, my whole philosophy on what we're trying to do down here changed,” Nedimyer said. “We were basically taking cuttings from these corals, growing them, and planting them on the reef. And what we found after 2023 is that none of the Founders can handle the heat in the Middle and Lower Keys.”
But it’s one thing to grow coral in an offshore nursery and try to breed those coral. Coral only spawn once a year. When depends on where and what kind of coral.
“ We started going out night after night after night in August, spending hours and hours and hours, and we finally figured out, okay, it's at, at about 10:20. But then we had no idea how to raise those babies,” Nedimyer said.
Turns out keeping coral alive in labs under artificial conditions is also hard work.
”It's a lot of daily care focusing on them,” Stickley said, explaining that of 10,000 larvae UM received in 2025, only sixty survived to reach their first birthday. “So we’re really, really proud.”
Planning for the Founders coral spawning started months in advance, Stickley said. Ultimately, a dozen universities and conservation groups pitched in, with teams arriving in Key Largo in late August to work shifts expected to last 12 days. They kept their fingers crossed the weather would cooperate.
Coral spawn at night, so divers needed to be in the water between 9:30 and 11:30 p.m. when Nedimyer had pinpointed spawning times.
”A lot of people have to work during the day, but we wanted to get a really big window because there's a lot of genotypes that Ken had at his nursery that nobody has ever seen spawn,” Stickley said. “ Seven or eight of the 12 nights we got spawning, so it was just really great to confirm that, yes, they are spawning in, in this window.”
A temporary fertilization lab was set up in a classroom at John Pennekamp Coral Reef State Park to handle the fertilization.
”If we didn't have that, I don't even know if we could have done this whole effort,” she said.
After the spawn was collected, boats would race back to the dock so the teams could transfer the bundles of spawn to the fertilization team. Aside from just tending to the coral, the team needed to keep track where they came from for breeding and research.
”We would separate the egg and the sperm of each parent, and then from that, we would do these targeted crosses, where we're crossing one specific mom with a specific dad,” Stickley said.
Once separated, the egg and sperm would sit for an hour to fertilize then be cleaned and packed in takeout food containers lined with tiny one-inch tiles to develop overnight. The AC in the classroom was cranked up to 82 degrees in the increasingly stinky classroom to keep water in the containers at 80 degrees. And operations last through the night.
”They're really fragile in those first 24 hours because it's literally cells dividing,” she said. “You're literally watching it go from a two-cell to a four-cell. It's really, really cool.”
A week after the spawn, the new babies were shipped out to labs across the state, to distribut the work load and limit losses in case a problem came up at a single lab, like a power outage or a broken pump.. Altogether 61,000 elkhorn larvae were created with over 100 different genetic crosses.
“This is what coral conservation looks like — long nights, precise science, and a team of people who are willing to show up when the opportunity comes,” O’Neill, the Florida Aquarium coral conservation program director, said in a statement. “Collecting elkhorn coral spawn in the ocean is an extremely challenging and demanding task, but our teams were committed to seeing it through.”
For Nedimyer, who has been diving in the Keys for more than 50 years and started his first coral nursery more than 25 years ago as a school project with his daughter, advances in coral restoration are a bit of a marvel.
“Ten years ago, this was unheard of, and now we're doing it,” he said. But he also worries that the restoration work won’t happen quickly enough.
“ This is the only way they're gonna recover is if we intervene and develop corals that can handle,” warming oceans, he said. “This is a process that would take a thousand years in normal conditions, but we don't have 1,000 years. We don't even have 10 years.”
