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

What 'Functional Extinction' Means

The near-total decline of these corals, which once formed the foundation of reefs in Florida and the Caribbean, means they are no longer able to play their previously crucial role in constructing and maintaining reef ecosystems that support a variety of marine life.

Functional extinction is a phase before global extinction, a danger that now hangs for many coral species.

Researchers recently warned that a critical threshold has been crossed, meaning corals around the world are likely to be eradicated due to global heating, which is raising ocean temperatures to intolerable levels.

Expert Insight

"Time is running out," said the lead author of the new Florida study. "Severe marine heatwaves are increasing in frequency and severity due to global warming, and without swift, decisive measures to reduce ocean heating and enhance coral survival, we face the danger of the disappearance of even more corals from reefs in Florida and worldwide."

Details of the Recent Study

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

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

The two species are intricate, reef-building corals and are named because they look like, respectively, the antlers of stags and elks.

However, researchers 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 catastrophic, losses.

Geographic Effects

• In the Florida Keys, mortality rates reached 98% and even one hundred percent, revealing a total eradication of the corals.
• In southeastern Florida, where temperatures have been cooler, mortality rates were reduced, at about thirty-eight percent.

Past and Present Threats

The two Acropora species had already endured from many years of localized impacts in Florida, such as poor water quality from pollutants that run off the land, as well as illness.

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

The 2023 heat event caused the ninth episode of bleaching on the Florida reef – a process 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 perish entirely.

Global Implications

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

This presents a significant danger to:

• One-fourth of all ocean life that relies upon what are effectively the marine rainforests.
• Hundreds of millions of people who rely on corals to support 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 worsened by rising global temperatures.

Conservation Efforts

In a last-ditch effort to avert a decline of endangered corals, scientists have established repositories of Acropora in marine facilities and ocean-based nurseries.

Efforts have been undertaken to replant corals on reefs in Florida, as well, in an effort to restore some of the 90% of coral cover lost off the state in the last forty years.

But as global heating continues to intensify, there is little hope of long-term survival of these species without significant actions, researchers warn.

Additional Expert Commentary

"Elkhorn corals, in particular, are some of the key wave-breaking coral species in the area," noted a study co-author, a marine biologist at the Miami University.

"They were once common on shallow reef tops 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 don't lose these corals completely."