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Researchers have found that two of the most important coral species comprising Florida's reef have become functionally extinct after a intense ocean heatwave caused devastating losses.

The Meaning Behind 'Functional Extinction' Signifies

The almost complete decline of these corals, which once formed the foundation of reefs in Florida and the Caribbean, means they can no longer fulfill their previously crucial role in building and sustaining reef ecosystems that support a diversity of marine life.

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

Researchers this month warned that a tipping point has been crossed, whereby corals globally are likely to be wiped out due to global heating, which is raising ocean temperatures to intolerable levels.

Expert Perspective

"We're running out of time," said the lead author of the recent research. "Severe marine heatwaves are increasing in frequency and severity due to climate change, and without swift, decisive measures to slow ocean warming and enhance coral survival, we risk the disappearance of additional coral species from reefs in Florida and worldwide."

The Recent Study

The new research, published in the Science journal, analyzed the outcome 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 fraying coral reefs to their highest levels in more than a century and a half.

The two species are complex, reef-building corals and are named because they look like, in turn, the horns of male deer and elk.

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

Geographic Effects

• In the Florida Keys, death rates reached ninety-eight percent and even one hundred percent, revealing a total eradication of the corals.
• In south-east Florida, where temperatures have been lower, mortality rates were reduced, at about 38%.

Historical and Present Dangers

The two Acropora species had already suffered from decades of localized impacts in Florida, such as poor water quality from contaminants that run off the land, as well as disease.

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

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

If temperatures stay high, the corals die off entirely.

Worldwide Consequences

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

This poses a significant danger to:

• A quarter of all ocean life that relies upon what are essentially the rainforests of the sea.
• Millions of people who rely on corals to support fish that they can consume and gain an income from.

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

Conservation Attempts

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

Efforts have been made to replant corals on reefs in Florida, too, in an effort to regain some of the ninety percent of coral cover lost off the state in the past four decades.

But as climate change continues to intensify, there is little hope of long-term survival of these species absent significant actions, scientists caution.

Additional Expert Commentary

"Elkhorn corals, in particular, are some of the most important 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 keep safeguarding our coastlines from inundation during storms, it is worthwhile taking extraordinary measures to ensure we don't lose these corals completely."