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Researchers have found that two of the most important coral species forming Florida's reef have become functionally extinct after a intense ocean heatwave caused catastrophic losses.

What 'Functional Extinction' Signifies

The almost complete decline of these corals, which once served as the foundation of reefs in Florida and the Caribbean, indicates they can no longer fulfill their once vital role in building and sustaining reef ecosystems that host a diversity of marine life.

Functional extinction is a stage before total extinction, a threat that now looms for many coral species.

Scientists this month warned that a tipping point has been crossed, meaning corals around the world are set to be eradicated due to climate change, which is raising ocean temperatures to intolerable levels.

Researcher Perspective

"Time is running out," said the lead author of the recent research. "Extreme heatwaves are becoming more frequent and intense due to climate change, and without swift, decisive measures to slow ocean warming and boost coral resilience, we face the danger of the disappearance of even more corals from reefs in Florida and around the world."

The New Research

The recent study, published in the journal Science, examined the outcome of staghorn and elkhorn coral corals off the Florida coast following a severe marine heatwave in 2023.

This event raised temperatures on Florida's fraying coral reefs to their highest levels in more than a century and a half.

The two species are intricate, reef-forming corals and are named because they resemble, respectively, the horns of male deer and elks.

However, scientists who performed diver surveys of more than 52,000 colonies of the species, across nearly four hundred sites along Florida's coast, found widespread, often devastating, losses.

Regional Effects

• Along the Florida Keys, death rates reached 98% and even one hundred percent, showing a total eradication of the corals.
• In south-east Florida, where temperatures have been cooler, mortality rates were lower, at about thirty-eight percent.

Historical and Present Threats

The two Acropora species had already suffered from many years of localized impacts in Florida, such as contaminated water from contaminants that wash off the land, as well as disease.

But the 2023 marine heatwave has been lethal for these heat-sensitive species.

The 2023 event caused the ninth occurrence of coral bleaching on the Florida reef – a phenomenon whereby corals become thermally stressed and expel the algae partners living in their tissues, causing them to become bleached white.

If temperatures stay high, the corals die off entirely.

Global Consequences

Worldwide, coral reefs are among the ecosystems most vulnerable to the human-caused climate emergency.

This presents a major threat to:

• A quarter of all ocean life that relies upon what are effectively the rainforests of the sea.
• Millions of people who rely on corals to support fish that they can consume and gain an income from.

Corals also act as a barrier to protect our shorelines from intense hurricanes, which are themselves being intensified by increasing global heat.

Conservation Efforts

In a last-ditch effort to avert a decline of endangered corals, scientists have established collections of Acropora in aquariums and offshore coral nurseries.

Efforts have been undertaken to replant corals on reefs in Florida, as well, in an effort to restore some of the ninety percent of coral cover disappeared off the state in the past four decades.

But as global heating continues to intensify, there is slim chance of continued existence of these species absent significant actions, scientists caution.

Further Expert Commentary

"Elkhorn corals, especially, are some of the most important wave-dampening coral species in the area," noted a study co-author, a marine biologist at the University of Miami.

"They used to be abundant on shallow reef crests in the Caribbean, and if we want our reefs to continue protecting our coastlines from inundation during storms, it is worthwhile taking exceptional steps to ensure we preserve these corals completely."