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Researchers have found that two of the key coral species forming Florida's reef are now functionally extinct after a intense 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 host a diversity of marine life.

Functional extinction is a stage before total extinction, a danger that now looms for many coral species.

Researchers recently alerted that a tipping point has been crossed, meaning corals around the world are set to be eradicated due to climate change, 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. "Severe marine heatwaves are becoming more frequent and intense due to global warming, and absent immediate, ambitious actions to reduce ocean heating and enhance coral survival, we risk the extinction of additional coral species from reefs in Florida and worldwide."

Details of the Recent Study

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

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

The two species are intricate, reef-forming corals and are identified because they look like, in turn, the horns of male deer and elk.

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

Geographic Impact

• Along the Florida Keys, death rates reached 98% and even one hundred percent, revealing a complete annihilation of the corals.
• In south-east Florida, where temperatures have been cooler, death rates were lower, at about thirty-eight percent.

Past and Current Threats

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

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

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

If temperatures stay high, the corals die off completely.

Global Consequences

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

This poses a significant danger to:

• A quarter of all ocean life that depends on what are essentially the rainforests of the sea.
• Millions of people who rely on 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 rising global temperatures.

Conservation Attempts

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

Efforts have been undertaken to reseed 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 continued existence of these species absent major interventions, researchers warn.

Further Expert Commentary

"Elkhorn corals, especially, are some of the most important wave-breaking coral species in the region," said a study co-author, a marine biologist at the University of Miami.

"They used to be 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 preserve these corals altogether."