Extreme Summer Heat Threatens Coral Replanting Effort

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Extreme Summer Heat Threatens Coral Replanting Effort

CLIMATEWIRE | Two months into 2024, water temperatures in the North Atlantic are off the charts — raising concerns this year will bring another wave of record-breaking marine heat.

Last year, sea surface temperature records toppled around the world, and about half the surface area of the world’s oceans experienced marine heat wave conditions by the end of the summer.

The high temperatures then and now are especially worrisome to experts working to protect Florida’s vulnerable coral reef — the only extensive reef system in the continental United States. And the heat is putting a damper on some efforts to bolster corals against future warming.


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The Coral Restoration Foundation, a marine conservation nonprofit based in the Florida Keys, has spent years growing new corals in offshore nurseries and then relocating them to the Florida reef, a process known as outplanting. It’s a strategy designed to bolster threatened and endangered coral species while improving the reef’s resilience to environmental disturbances.

CRF participates in a collaborative initiative spearheaded by NOAA known as Mission: Iconic Reefs, which aims to restore around 3 million square feet of coral reefs across seven sites in the Florida Keys National Marine Sanctuary. Transplanting new corals to the reef is a big part of those efforts.

But CRF, which is one of the world’s largest reef restoration organizations, has decided to press pause this year on most of its outplanting activities.

Marine heat last year wiped out more than half the group’s nursery stocks. And while they were still left with about 20,000 corals — down from 50,000 before the heat struck — they hope to spend much of this year building their numbers back up again.

But it could be tough. Restoration experts are worried about another extreme summer. If this year’s temperatures rival last year’s, much of the reef could bleach or die for the second year in a row.

“It’s not the best decision to do a huge charge into outplanting again in what could be another difficult or extreme year,” said Jessica Levy, CRF’s restoration program manager.

Widespread bleaching

Ocean temperatures reached their hottest levels on record in 2023, particularly in the North Atlantic.

The European Union’s Copernicus Climate Change Service reported that sea surface temperatures across the region hit a record of 77.34 degrees Fahrenheit on Aug. 31, while temperatures for the month hovered about 1.69 degrees above average.

Florida saw some of the strongest heat seen anywhere. Water temperatures in Manatee Bay, not far from Key Largo, appeared to set a new world record in July when a buoy reported a jaw-dropping reading of 101.1 F.

Florida corals suffered devastating casualties as a result.

The reef experienced widespread bleaching, a phenomenon in which stressed corals turn bone white after expelling the colorful algae living inside them. Bleached corals still can survive if they’re given adequate time to recover. But many corals last year ultimately died.

And in some places, water temperatures were so hot that corals died before they even had a chance to bleach, Levy said. The tissue simply sloughed right off their skeletons, as though they had melted into the scalding water.

A recent NOAA study of five key reef sites found that less than 22 percent of the staghorn coral at surveyed locations remained alive. Living specimens were found only at the two most northern reefs surveyed: Carysfort Reef and Horseshoe Reef.

Live elkhorn coral was found at only three reef sites. And no staghorn or elkhorn corals were observed at the Looe Key Reef in the lower Florida Keys.

That’s bad news for the Florida reef. Staghorn and elkhorn corals were historically the dominant species in the area, according to Levy, and they provide habitat for fish and other marine organisms. Both species are listed as threatened under the Endangered Species Act. They’re also two of the key species that CRF works with in its outplanting efforts.

When extreme heat struck last summer, CRF staff members rushed to save as many of their growing corals as they could, trucking them from their offshore nurseries into land-based facilities in places such as Sarasota and Palm Beach.

Over the last few months, since temperatures have cooled, they’ve begun transporting the corals back to their offshore sites. They’re now turning their attention to building up their stocks again in hopes of restarting their outplanting efforts with a full arsenal in the future.

But the worsening impacts of climate change loom large.

Temperatures in the North Atlantic continue to hover well above their average levels in 2024, with summer lurking just around the corner.

“It has been record-breaking warm for an entire year, often by seemingly-impossible margins,” said Brian McNoldy, an ocean expert at the University of Miami, in a recent post on X, formerly known as Twitter.

And marine heat waves are expected to grow more frequent and more intense in the coming years as global temperatures rise. That leaves the future of coral restoration initiatives, like CRF’s outplanting efforts, increasingly uncertain.

Extreme heat is one of the biggest threats facing coral reefs today, and halting climate change is ultimately the only way to address it. But other environmental stressors, such as pollution and overfishing, can make them more vulnerable.

Highlighting the problem could help motivate policymakers to mitigate some of these additional stressors, Levy noted — potentially buying coral reefs more time in the short term.

CRF and other coral restoration groups also are paying greater attention to genetics these days, Levy added, studying which coral species are the most resilient to extreme heat and making efforts to bolster those populations on vulnerable reefs. They’re also working to catalog as much of the reef’s surviving genetic diversity as possible and bank genetic material in secure, land-based facilities so they won’t be lost forever during future bleaching events.

Levy also hopes that extreme events, such as last summer’s heat, will put a spotlight on the plight of the world’s coral reefs.

“If this event did anything, it is that it’s made people really pay attention, and it’s started conversations about what does restoration success mean and what does it look like,” Levy said. “Particularly if you — and by you, I mean the world, the collective you — can’t pull back on the effects of climate change, can’t ameliorate what’s coming.”

Reprinted from E&E News with permission from POLITICO, LLC. Copyright 2024. E&E News provides essential news for energy and environment professionals.

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