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

What 'Functional Extinction' Signifies

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

Ecological extinction is a phase before total extinction, a danger that now looms for many coral species.

Scientists this month warned that a critical threshold has been crossed, whereby corals globally are set to be wiped out due to global heating, which is increasing ocean temperatures to unbearable levels.

Researcher Insight

"We're running out of time," said the lead author of the new Florida study. "Extreme heatwaves are increasing in frequency and severity due to global warming, and absent immediate, ambitious actions to reduce ocean heating and boost coral resilience, we risk the extinction of even more corals from reefs in Florida and worldwide."

The Recent Study

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

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

The two species are complex, reef-forming corals and are named because they look like, in turn, the antlers of stags and elk.

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

Geographic Impact

• In the Florida Keys, death rates reached ninety-eight percent and even 100%, revealing a total eradication of the corals.
• In southeastern Florida, where temperatures have been cooler, death rates were reduced, at about 38%.

Historical and Current Threats

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

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

The 2023 event caused the ninth episode of coral bleaching on the Florida reef – a process whereby corals become heat-stressed and expel the symbiotic algae living in their tissues, causing them to become bleached white.

If temperatures stay high, the corals die off entirely.

Worldwide Consequences

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

This presents a significant danger to:

• One-fourth of all ocean life that depends on what are essentially the rainforests of the sea.
• Hundreds of millions of people who rely on corals to sustain fish that they can eat and gain an income from.

Corals also serve as a barrier to protect our shorelines from intense hurricanes, which are themselves being intensified by increasing global heat.

Preservation Attempts

In a desperate attempt to prevent a death spiral of threatened corals, scientists have established repositories of Acropora in aquariums and ocean-based nurseries.

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

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

Additional Expert Commentary

"Elkhorn corals, in particular, are some of the key wave-dampening coral species in the area," noted 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 keep safeguarding our coastlines from inundation during storms, it is worthwhile taking exceptional steps to ensure we preserve these corals altogether."