As ocean temps cool, divers start returning Florida’s rescued corals back to sea

Cynthia Lewis is finally catching her breath.

For nearly four months, Lewis has overseen a lab in the Florida Keys housing more than 5,000 refugee corals rescued from scorching offshore waters.

Her staff at the Keys Marine Laboratory on Long Key have faced swirls of heartbreak and hope since mid-July — when a mass coral evacuation began.

Heartbreak came in those first few weeks when scores of elkhorn and staghorn corals arrived at the lab, bleached or dead, as an unprecedented marine heat wave swept through offshore coral nurseries. Temperatures pushing the mid-90s arrived sooner than anticipated and caught the restoration community off-guard.

And then came the hope, however fleeting, that the first-of-its-kind evacuation and rescue operation was helping keep many corals alive. Corals regained their color and strength and in recent days have passed veterinarian health inspections.

Now, Lewis is finally coming up for air as the immediate coral crisis abates . On Monday, a restoration team took roughly 360 corals from the lab and drove them north to Tavernier, where divers boated the animals back to their offshore nurseries. The 13-hour operation was the first journey in what could be a weekslong effort to put every rescued coral back at sea.

“So many of these corals came in gasping their last breath,” said Lewis, the lab’s director. “Every single coral that we can put back out there is a success.”

As of mid-September, Florida’s coral reefs — the only coral reef system in the continental United States — faced the equivalent of nearly 24 weeks of harmful ocean temperatures, according to the National Oceanic and Atmospheric Administration’s Coral Reef Watch.

With water that hot, for that long, vast swaths of offshore corals in the Keys died after bleaching earlier in the summer. Corals lose their color and bleach, a signal of prolonged stress, when they expel the tiny algae species living in their tissues.

It could be months before scientists know the true extent of the damage and loss to Florida’s reef, according to Jacquie De La Cour, the operations manager at Coral Reef Watch. It’s still unclear how already vulnerable corals will now respond to disease, potentially exacerbating the mortality crisis.

But for now, coral restorers are celebrating the small victory of returning the first batch of healing corals back to their offshore Tavernier nursery. Ocean temperatures in recent weeks have dipped to 80 degrees Fahrenheit, roughly 12 degrees cooler than the summer peak.

Stormy seas finally calmed this week and gave divers a short window to kick off the initial return mission, according to Phanor Montoya-Maya, the reef restoration program manager for the Coral Restoration Foundation. He said all rescued corals should hopefully be out of the Keys Marine Laboratory and back to their offshore homes by December.

“These are challenging times,” Montoya-Maya said in an interview Tuesday. But morale was high Monday as the first corals were planted back on the seafloor. “We can take this as an opportunity to continue learning from the crisis, and sharing with others not just how bad things can get, but also what the good things are that we can do.”

New ideas born from coral crisis

Unprecedented heat caused coral restorers to come up with unprecedented solutions.

One idea that stemmed from the crisis was to relocate corals to deeper, cooler ocean waters instead of bringing them to land-based labs.

Ken Nedimyer, the founder and technical director of the nonprofit Reef Renewal USA, Inc., helped spearhead the experimental effort to bring corals to colder, 70-feet-deep waters. In late July, there was a roughly 2-degree water temperature difference from the hotter water in the shallows.

About 40 divers from all over the world traveled to the Keys to help with the relocation, Nedimyer said.

“Getting them there and then getting them out of the sun seemed to make all the difference in the world,” he said. Every two weeks, divers would score the corals’ health from 0 to 5, with zero being healthy and five being bleached bone-white. Within a few weeks, the corals brought to deeper waters had improved to a 1.

“They looked really good, and they’ve stayed healthy,” Nedimyer said in an interview. Teams hope to start bringing the corals back to shallower water as soon as rough seas calm in the deeper waters, he said.

Warm summer water temperatures lasting into fall meant restoration efforts had to wait until cooler waters finally returned to South Florida, said Liv Williamson, an assistant scientist of marine biology and ecology at the University of Miami.

“It was cold the other day,” Williamson said. “Two months ago you were baking in the water.”

During recent dives in the Florida Keys, Williamson said, she was happy to find corals she had watched bleach this summer were recovering and regaining their color.

It’s not just the Keys Marine Laboratory returning rescued corals back to sea. Over the last few weeks, the University of Miami has returned hundreds of staghorn and elkhorn corals from about 150 genetically unique individuals.

“We want to make sure we have lots and lots of genotypes because that’s where the genetic diversity comes from,” Williamson said. “And genetic diversity equals resilience.”

Williamson said one silver lining of this summer’s bleaching crisis is an increased awareness of the need for a healthy reef in Florida.

“I feel confident that there’s a lot of attention on it and, therefore, there’ll be funding and people to do as much as we can do,” she said. “It’s a question of whether what we’re capable of doing is enough.”

Williamson said climate change shares much of the blame for the extreme temperatures, which were made worse by this year’s El Niño.

Her research focuses on finding more resilient corals and helping pass on their heat-tolerant genes to outplanted corals, in an effort to keep up with warming oceans.

Williamson and her team are monitoring the new corals spawned earlier this summer to see if their heat tolerance matches those in the parent corals.

“That’s ongoing for the next bunch of months — really into next year,” she said.

‘We’re crossing our fingers’

The coral community was surprised by how early the heat actually arrived this past summer. Despite widespread collaboration, branching corals like the elkhorn and staghorn species saw high mortality rates, Lewis said.

With an El Niño weather pattern likely to linger through next year and the effects of climate change exacerbating extreme heat, coral scientists are bracing for the worst again next summer. The Keys Marine Laboratory will be better prepared if a similar marine heat wave strikes next year or in the more distant future. For Lewis, it’s a matter of when, not if.

“We’re crossing our fingers, but the bottom line is this: We’re better prepared for the next time,” Lewis said.

The lab, casually dubbed by scientists as a “coral halfway house,” is home to 60 saltwater tanks that range in size from 40 gallons to 1,000 gallons. The lab is just south of Islamorada and right in the middle of the Florida Keys island chain, making it a central landing spot for several coral rescue groups.

Before the coral crisis began, the lab had fewer than 40 water pumps to keep saltwater flowing over corals to mimic ocean currents. But the sheer amount of rescued coral pouring into the facility this past summer forced the lab to triple the number of pumps to 120.

The tally of new equipment helps underscore that emergency growth: The lab now has 20 new tables for housing saltwater tanks and new adjustable shades to veil corals from harsh sunlight, and discussions already are underway to expand the facility further — all to prepare for the inevitability of a future marine heat wave, Lewis said.

“Everything happened so fast,” Lewis said. “But we’ve learned an awful lot about keeping these very highly stressed corals in captivity.”