by Record-warming seawater has killed more than three-quarters of the human-cultivated corals that scientists planted in the Florida Keys in recent years in an effort to support a threatened species that is highly vulnerable to climate change, researchers have found.
Researchers from the National Oceanic and Atmospheric Administration returned this week to five reefs where they planted staghorn and elkhorn coral, both classified as threatened on the endangered species list, to see how the critters have repopulated. seeing long water temperatures in the 90s (30s Celsius). last summer and fall. Most of them were not. They observed widespread mortality in repopulated and wild corals on five Florida Keys reefs.
Scientists blame human-caused climate change, with a natural El Nino boost, for making the water too warm for the delicate, animal-like coral to survive. After trying to rescue corals during last summer’s heat, this was scientists’ first winter look to see what survived.
Only 22% of the 1,500 repopulated staghorn corals they surveyed were still alive, NOAA said. Only about 5% of 1,000 replanted elkhorn corals survived. At Looe Key, the southernmost of the reefs they looked at, “we found no live elkhorn or staghorn corals, not wild, not planted,” said coral biologist Katey Lesneski, research and monitoring coordinator for the NOAA Mission : Iconic Reefs.
“It’s a terrible thing to witness,” Lesneski said in an interview just two days after completing the dives. “In addition to thinking about the economic and ecological benefits these reefs and corals provide, there is the loss of the intrinsic beauty that many people come to the Keys to experience. And losing that is also very worrying.”
“There’s still a lot of data to be collected to really understand the full impact,” Lesneski said. “But we certainly haven’t seen anything like this in recorded human history.”
These are usually corals with strong colors of red, orange, tan and brown. But what Lesneski and other researchers saw when they had the pigeon was dead coral with brown-green algae settled on the lifeless skeleton to make it look “pretty,” she said.
Not only are staghorn and elkhorn populations declining so much that they are on the endangered list, but they are vital to the vast community of different types of coral because they are framework builders that provide the “structural framework” for coral habitat, Lesneski said.
While the researchers were diving to check on the human-planted coral at Horseshoe Reef, the second northernmost reef they looked at, an area Lesneski was looking at was once a wild colony of elkhorn coral. which was more than 100 years old.
“I saw them in June and they were alive. In July, they were starting to die from the heat stress,” Lesneski said. “And at this point we haven’t even found a patch of living tissue on any of those wild colonies at Horseshoe Reef. So it was very difficult to see that.”
In the five reefs the team visited, they saw some wild corals alive and well, Lesneski said. Brain or boulder corals seemed to do better, but there was still a high death toll, she said.
The joint federal-private project plans to spend at least $97 million to plant coral species grown on land or in ocean nurseries at seven sites. Some of the species are the same as what was already in the water and were badly hurt by warmer seas, but some were cross-bred to be heartier, Lesneski said. It’s too early to tell whether the heartiest coral has survived longer, she said.
NOAA measured water temperature days at the planting sites hitting 93 degrees (34 degrees Celsius) while reaching 94 degrees at another site, Lesneski said. She and others said that is too hot.
“What happened in 2023 was shocking,” said Mark Eakin, NOAA’s retired chief of coral monitoring, who is now corresponding secretary of the International Coral Reef Association. “They were actually seeing temperatures they didn’t think were possible.”
Although coral reefs in the Caribbean were destroyed during last year’s high water temperatures, “2023 was not as bad as we feared in the rest of the world,” Eakin said.
Earlier this month, NOAA revised its coral reef watch alert system to add new higher levels of heat stress categories due to worsening climate change. It’s the equivalent of adding a Category 6 to a hurricane, Lesneski said.
Both Eakin and University of Victoria coral biologist Julia Baum said this raises legitimate concerns about trying to repopulate coral reefs by returning the coral to water that’s getting too warm.
“Climate change will almost certainly cause coral restoration to fail,” Baum said in an email. “Trying to restore coral in today’s warm ocean is like trying to restore a house while it’s still on fire.”
“Our oceans are very warm for corals now and continue to warm because of climate change,” Baum said.
Lesneski said she understands that concern and that researchers are trying to see what they can do to breed more heat-resistant corals.
“It’s not a silver bullet,” Lesneski said. “There must be global reductions in fossil fuel derived emissions, major policy changes. But for now, if we want to have any of the economic or ecological benefits of reefs, we must do our best to conserve, be good stewards and restore as much as we can. “
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