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

The Meaning Behind 'Functional Extinction' Means

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

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

Researchers this month warned that a critical threshold had been reached, whereby corals around the world are set to be wiped out due to climate change, which is raising ocean temperatures to unbearable levels.

Expert Insight

"We're running out of time," said Ross Cunning of the new Florida study. "Extreme heatwaves are increasing in frequency and severity due to global warming, and absent swift, decisive measures to reduce ocean heating and enhance coral survival, we risk the disappearance of even more corals from reefs in Florida and around the world."

The New Research

The recent study, featured in the Science journal, analyzed 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 peak temperatures in over 150 years.

The two species are intricate, reef-forming corals and are identified because they look like, respectively, the horns of male deer and elk.

However, researchers who conducted diver surveys of over fifty-two thousand colonies of the species, across 391 sites along Florida's coast, found widespread, often catastrophic, losses.

Regional Impact

• In the Florida Keys, mortality rates reached ninety-eight percent and even one hundred percent, showing a complete annihilation of the corals.
• In southeastern Florida, where temperatures have been cooler, mortality rates were lower, at about thirty-eight percent.

Past and Current Threats

The two Acropora species had already suffered from many years of regional pressures in Florida, such as contaminated water from contaminants that run off the land, as well as illness.

But the 2023 heatwave has been fatal for these temperature-sensitive species.

The 2023 heat event caused the ninth episode 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 remain elevated, the corals die off completely.

Global Implications

Globally, coral reefs are among the ecosystems most at risk to the human-caused climate crisis.

This poses a significant danger to:

• One-fourth of all ocean life that depends on what are effectively the marine rainforests.
• Millions of people who depend upon corals to sustain fish that they can eat and gain an income from.

Corals also serve as a protective barrier to safeguard our shorelines from powerful storms, which are themselves being intensified by rising global temperatures.

Preservation Efforts

In a last-ditch effort to avert a decline of threatened corals, scientists have created collections of Acropora in aquariums and ocean-based nurseries.

Efforts have been made to replant corals on reefs in Florida, too, in an effort to regain some of the 90% of coral cover lost off the state in the past four decades.

But as climate change continues to intensify, there is little hope of continued existence of these species absent significant actions, researchers warn.

Additional Expert Commentary

"Elkhorn species, especially, are some of the most important wave-breaking coral species in the region," noted Andrew Baker, a ocean scientist at the Miami University.

"They used to be common on shallow reef tops in the Caribbean, and if we want our reefs to keep safeguarding our coastlines from inundation during storms, its worth taking extraordinary measures to ensure we don't lose these corals altogether."