Plate Nº 56 · recorded October 10, 2026
Earth & ClimateReported finding
Diseased Florida Keys Coral Faced Nearly 4x Death Risk in 2023 Heat Wave
A University of Georgia study finds coral with preexisting disease died at almost four times the rate of healthy coral during a 41-day 2023 Florida Keys heat wave that exceeded 87°F.
By James Calloway3 min read690 words
In brief
- Water temperatures exceeded 87°F (31°C) for 41 consecutive days in summer 2023
- Coral with preexisting disease had nearly 4x higher death risk than healthy coral
- Healthy coral tissue next to diseased coral was almost 2x as likely to die
- Elkhorn coral suffered catastrophic losses during the 2023 heat wave
- Worldwide coral cover has dropped by more than two-thirds since 1972
Coral colonies already battling disease died at nearly four times the rate of healthy coral during a 2023 Florida Keys heat wave that kept water temperatures above 87°F (31°C) for 41 consecutive days, according to a new University of Georgia study.
Published in the journal Coral Reefs, the paper adds hard numbers to a trend coral scientists have watched for years: as oceans warm, reef-building corals are running out of margin to cope.
What did the study measure?
The research team, led by doctoral student Camilla Nivison of the Odum School of Ecology, surveyed hundreds of square feet of coral colonies in the Florida Keys during the summer of 2023. They used high-resolution 3D layered photo imaging and underwater mapping to track which colonies lived, which bleached, and which died.
That summer was not ordinary. Every late summer heats the Keys, but 2023 broke every record. A heat wave pushed water past 87°F for 41 straight days. Every summer since has matched or exceeded those temperatures.
The team then compared coral that had preexisting disease lesions against healthy coral during and after the heat event.
How much did disease raise the danger?
The study reports that corals carrying disease lesions faced a nearly four times higher risk of dying from heat than healthy corals. Bleaching, the loss of symbiotic algae that feed the coral and give it color, swept through the colonies. Once bleaching starts, corals grow more vulnerable to disease and starvation as their microbiome breaks down.
The damage did not stop at the lesion. Healthy coral tissue directly next to diseased coral was almost twice as likely to die under extreme heat as healthy tissue sitting farther away.
"Multiple stressors are not a good thing," Nivison said. "When the corals are handling threats from multiple things at the same time, unsurprisingly, that makes it more challenging for them to survive."
Which corals took the worst hit?
Elkhorn coral suffered catastrophic losses. James Porter, co-author of the study and the Josiah Meigs Distinguished Professor Emeritus at UGA's Odum School, framed the scale of that decline in stark terms.
"This coral used to be the most common coral in the Caribbean," Porter said. "The loss of this coral throughout the Caribbean is comparable to the death of oak trees from Maine to Florida."
Porter has watched reefs decline for more than half a century. "Since I began diving in 1972, we've lost more than two-thirds of all living coral worldwide," he said.
Where did corals survive?
Not every reef fared the same. The researchers found oasis patches with minimal damage scattered across the survey area.
"We found some reefs during the heat wave to be an oasis with minimal damage," Nivison said. "Nobody's been able to pin down exactly why, but it appears that topography is important."
The common thread: corals on reef edges did better. Faster water movement across the edge sweeps metabolic waste away and brings new food particles in. That flow seems to shield stressed tissue.
"The more water is moving across, the more it's removing things that are diffusing out of the coral, specifically metabolic wastes," Nivison said. "That helps protect the coral tissue, especially when it is stressed by heat."
What can conservationists actually do?
The findings translate into two practical levers:
- Target restoration at reef edges, where water movement helps corals cope with heat stress.
- Reduce coastal pollution, which feeds the pathogenic bacteria and nutrient loads that trigger coral disease.
"You can't change the whole globe, but you can do a lot of work toward mitigating local pollution and improving local water quality," Porter said.
The study carries a sobering caveat. The researchers examined a single season in a single region. Longer-term monitoring will show whether the same pattern holds across other reefs and other heat waves. Still, the numbers are large enough that reef managers say they cannot wait.
The paper, "Coral mortality in a mass bleaching event influenced by proximity to diseased tissue and reef topography," appeared in Coral Reefs in 2026 (DOI: 10.1007/s00338-026-02928-6).
via Phys.org Biology (Source)
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Staff writer covering marketplaces and e-commerce at SciBeat.
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