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Researchers have found that two of the primary coral species forming Florida's reef are now functionally extinct after a withering ocean heatwave led to catastrophic losses.

What 'Functional Extinction' Means

The almost complete decline of these corals, which once served as the backbone of reefs in Florida and the Caribbean, indicates they can no longer play their previously crucial role in constructing and maintaining reef ecosystems that support a diversity of marine life.

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

Researchers recently warned that a critical threshold had been reached, meaning corals globally are likely to be wiped out due to climate change, which is raising ocean temperatures to intolerable levels.

Researcher Perspective

"We're running out of time," said the lead author of the recent research. "Extreme heatwaves are becoming more frequent and intense due to global warming, and without immediate, ambitious actions to reduce ocean heating and enhance coral survival, we risk the extinction of even more corals from reefs in Florida and worldwide."

The New Research

The recent study, featured in the journal Science, analyzed the outcome of staghorn and elkhorn corals off the Florida coast after a severe marine heatwave in 2023.

This event raised temperatures on Florida's fraying coral reefs to their highest levels in over 150 years.

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

However, researchers who performed underwater surveys of more than 52,000 colonies of the species, across 391 sites along Florida's coast, found extensive, often devastating, losses.

Geographic Effects

• Along the Florida Keys, death rates hit 98% and even one hundred percent, showing a complete annihilation of the corals.
• In southeastern Florida, where temperatures have been cooler, mortality rates were reduced, 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 poor water quality from pollutants that run off the land, as well as illness.

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

The 2023 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 entirely.

Worldwide Implications

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

This presents a significant danger to:

• A quarter of all ocean life that depends on what are essentially the marine rainforests.
• Hundreds of millions of people who depend upon corals to support fish that they can consume and earn a livelihood from.

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

Conservation Efforts

In a desperate attempt to prevent a death spiral of threatened corals, scientists have established collections of Acropora in marine facilities and offshore coral nurseries.

Attempts have been made to reseed corals on reefs in Florida, as well, in an effort to regain some of the 90% of coral cover lost off the state in the last forty years.

But as climate change continues to intensify, there is slim chance of long-term survival of these species without major interventions, researchers warn.

Further Researcher Insight

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

"They were once abundant on shallow reef tops in the Caribbean, and if we want our reefs to continue protecting our coastlines from inundation during storms, its worth taking extraordinary measures to ensure we preserve these corals completely."