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Scientists have discovered that two of the most important coral species forming Florida's reef have become functionally extinct following a intense ocean heatwave led to catastrophic losses.

What 'Functional Extinction' Means

The almost complete collapse of these corals, which once served as 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 host a variety of marine life.

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

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

Expert Perspective

"Time is running out," said Ross Cunning of the recent research. "Severe marine heatwaves are increasing in frequency and severity due to global warming, and absent immediate, ambitious actions to reduce ocean heating and enhance coral survival, we risk the disappearance of additional coral species from reefs in Florida and worldwide."

Details of the New Research

The new research, published in the Science journal, examined the fate of staghorn coral and elkhorn coral corals off the Florida coast following a intense marine heatwave in 2023.

This event elevated temperatures on Florida's deteriorating coral reefs to their peak temperatures in over 150 years.

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

However, scientists who performed diver surveys of over fifty-two thousand colonies of the species, across 391 sites along Florida's coast, found extensive, often devastating, losses.

Regional Impact

• In the Florida Keys, mortality rates reached ninety-eight percent and even 100%, revealing a complete annihilation of the corals.
• In south-east Florida, where temperatures have been cooler, mortality rates were lower, at about thirty-eight percent.

Past and Present Dangers

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

But the 2023 marine heatwave has proved fatal 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 ghostly white.

If temperatures remain elevated, the corals die off entirely.

Worldwide Consequences

Worldwide, coral reefs are among the ecosystems most at risk to the anthropogenic climate crisis.

This poses a significant danger to:

• A quarter of all ocean life that relies upon what are effectively the marine rainforests.
• Hundreds of 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 protect our shorelines from intense hurricanes, which are themselves being intensified by increasing global heat.

Conservation Attempts

In a last-ditch effort to avert a death spiral of endangered corals, scientists have established collections of Acropora in marine facilities and offshore coral nurseries.

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

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

Further Researcher Insight

"Elkhorn corals, in particular, are some of the key wave-dampening coral species in the area," said a study co-author, a ocean scientist at the Miami University.

"They used to be abundant on shallow reef tops in the Caribbean, and if we want our reefs to continue protecting our coastlines from flooding during storms, its worth taking exceptional steps to ensure we don't lose these corals completely."