(Bloomberg) -- More than two months after a record-setting marine heat wave started off the coast of southern Florida, Ian Enochs, a research ecologist with the National Oceanic and Atmospheric Administration, delivered a coral status update like an ER doctor comforting the family of a sick patient.
“We were really happy to see — and happy is not a word we use a lot with reefs these days — some color returning in some of the species,” Enochs told Bloomberg Green in a Sept. 18 update on the Cheeca Rocks in the Upper Keys. “There was definitely death and mortality that has occurred, but for some of the corals, especially in the shadier sides of the colonies,” there are signs of recovery, he said.
Just a few weeks prior, Cheeca Rocks’ corals were struggling. Starting in early July, the combination of an El Niño weather pattern and continued global warming spurred marine heat waves that by August impacted nearly 40% of the world’s oceans. Off the coast of southern Florida, researchers were by mid-July observing bath-like ocean temperatures of 90F (32C) and above.
“In the Florida Keys, sea temperatures broke the previous record for the highest value ever measured by satellite on July 9,” Derek Manzello, head of NOAA’s Coral Reef Watch program, said during a press conference in August. “And temperatures have been higher than the prior record for 28 of the past 37 days." While that heat has since eased, it hasn’t dissipated entirely, leaving impacted coral in a near-constant state of stress.
Reef-building coral have a symbiotic relationship with algae, which live on the reef structure and give the coral color while also providing the bulk of the coral’s food and energy. When waters heat up, though, that same algae harms the coral, which expels it in a process known as bleaching (when the algae goes, so does the color). Bleached coral enters into a period of starvation that, if unchecked, eventually leads to death.
Read more: Rising Temperatures Are Wreaking Havoc Year-Round
By late July, only a few weeks after the ocean temperatures started ticking up, NOAA researchers were getting reports of widespread coral bleaching across the Florida Keys. By mid-August, bleaching had also been confirmed on both sides of the Yucatan Peninsula off Mexico, Belize, Cuba, Panama, Puerto Rico, and the US Virgin Islands.
Enochs, who has been studying the Cheeca Rocks reef for about a decade, witnessed what he described as the worst bleaching he’s ever seen there. He calls Cheeca Rocks one of the most “successful, resilient, persistent reefs in the Florida Keys,” but by August, “it was way worse than I imagined,” Enochs said. “It was every single coral that was affected. It’s hard to be more catastrophic.”
While bleaching doesn’t mean certain death for coral, its severity and duration does impact whether and how quickly a reef might recover. In August, with more weeks of marine heat ahead, Enochs’ team could only watch and wait. “My hope is some corals will survive,” he said at the time. “I would love for these corals to be able to regain their color and live.”
When Enochs’ team next set out for Cheeca Rocks in early September, they braced for the worst. This time they were pleasantly surprised.
Some of the coral had already died, and it’s an open question as to how much of the corals might still succumb to disease or death, especially if ocean temperatures stay elevated. But stormy, rainy weather has also kept the ocean waters murky — bad conditions for photographing and collecting data, but “good for coral enduring,” Enochs said. (Anything that blocks sunlight can offer coral relief.)
One more week later, and the researchers were able to identify both a mix of dead or dying coral and, remarkably, a cohort of corals that were regaining their color. “I am amazed by how persistent these corals are,” Enochs said. “But I'm also equally amazed by how difficult the conditions that are being thrown at them are.”
Enochs’ team is still processing data, and doesn’t yet have exact statistics on how many corals died or the current state of bleaching. Even if they did, the ocean heat wave isn’t over, meaning the scientists won’t know the reef’s fate for many more months. “We’re not out of the woods,” he said.
But the severity of the heat wave is already forcing Enochs and other researchers to rethink their strategies for protecting corals amid worsening global warming. Any sign of resilience is met with both celebration and plans for further study.
Seeing how the marine heat wave has killed so many corals “has really changed my perspective and I believe the perspective of many of my colleagues,” Enochs said, adding that “it has lit a fire” in the scientific community to urgently find new ways to restore and treat injured corals.
(Clarifies the region of the reef surveyed in second paragraph.)
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