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Scientists have discovered that two of the key coral species forming Florida's reef are now functionally extinct following a intense ocean heatwave caused 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 play their previously crucial role in constructing and maintaining reef ecosystems that host a diversity of marine life.

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

Scientists this month alerted that a critical threshold had been reached, whereby corals around the world 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 the lead author of the recent research. "Severe marine heatwaves are increasing in frequency and severity due to global warming, and without swift, decisive measures to slow ocean warming and boost coral resilience, we risk the disappearance of additional coral species from reefs in Florida and around the world."

The Recent Study

The recent study, featured in the journal Science, examined the outcome of staghorn and elkhorn corals off the Florida coast after a severe 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 intricate, reef-building corals and are named because they look like, respectively, the horns of male deer and elk.

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

Geographic Effects

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

Past and Current Dangers

The two Acropora species had already endured from decades of regional pressures 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 algae partners living in their tissues, causing them to become bleached white.

If temperatures stay high, the corals die off entirely.

Global Consequences

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

This poses a major threat to:

• One-fourth of all ocean life that depends on what are effectively the rainforests of the sea.
• Hundreds of millions of people who depend upon corals to support fish that they can consume and gain an income from.

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

Preservation Attempts

In a desperate attempt to prevent a decline of threatened corals, scientists have established collections of Acropora in marine facilities and ocean-based nurseries.

Efforts have been made to replant corals on reefs in Florida, as well, in an effort to regain some of the ninety percent of coral cover lost off the state in the last forty years.

But as climate change continues to escalate, there is little hope of continued existence of these species without significant actions, scientists caution.

Additional Expert Commentary

"Elkhorn species, especially, are some of the key wave-dampening coral species in the area," said a study co-author, a marine biologist at the Miami University.

"They were once common on shallow reef crests in the Caribbean, and if we want our reefs to continue protecting our coastlines from inundation during storms, it is worthwhile taking extraordinary measures to ensure we don't lose these corals altogether."