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

The Meaning Behind 'Functional Extinction' Means

The almost complete decline of these corals, which once formed the backbone of reefs in Florida and the Caribbean, indicates they are no longer able to fulfill their once vital role in constructing and maintaining reef ecosystems that host a variety of marine life.

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

Researchers recently alerted that a critical threshold has been crossed, whereby corals globally are set to be wiped out due to climate change, which is increasing ocean temperatures to unbearable levels.

Researcher Insight

"We're running out of time," stated Ross Cunning of the recent research. "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 additional coral species from reefs in Florida and around the world."

The New Research

The recent study, published in the journal Science, examined the fate of staghorn coral and elkhorn coral corals off the Florida coast after 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 complex, reef-building corals and are identified because they resemble, in turn, the horns of male deer and elk.

However, scientists who conducted diver surveys of more than 52,000 colonies of the species, across 391 sites along Florida's coast, found widespread, often devastating, losses.

Geographic Impact

• In the Florida Keys, death rates hit 98% and even 100%, revealing a complete annihilation of the corals.
• In south-east Florida, where temperatures have been lower, death rates were reduced, at about 38%.

Past and Present Threats

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

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

The 2023 heat event caused the ninth occurrence of 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 completely.

Worldwide Implications

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

This poses a major threat to:

• A quarter of all ocean life that relies upon what are effectively the rainforests of the sea.
• Hundreds of millions of people who depend upon corals to support fish that they can eat and earn a livelihood from.

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

Preservation Attempts

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

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

But as climate change continues to escalate, there is little hope of long-term survival of these species without major interventions, scientists caution.

Additional Researcher Insight

"Elkhorn species, in particular, are some of the key wave-breaking coral species in the area," said a study co-author, a marine biologist 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 preserve these corals altogether."