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Scientists have discovered that two of the most important coral species forming Florida's reef have become ecologically extinct following a intense ocean heatwave caused catastrophic losses.

The Meaning Behind 'Functional Extinction' Means

The near-total decline of these corals, which once formed the backbone of reefs in Florida and the Caribbean, indicates they can no longer play their once vital role in constructing and maintaining reef ecosystems that host a diversity of marine life.

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

Scientists this month alerted that a tipping point has been crossed, meaning corals globally are likely to be eradicated due to climate change, which is raising ocean temperatures to intolerable levels.

Researcher Perspective

"We're running out of time," stated Ross Cunning of the new Florida study. "Severe marine heatwaves are becoming more frequent and intense due to climate change, and absent immediate, ambitious actions to slow ocean warming and enhance coral survival, we risk the disappearance of even more corals from reefs in Florida and worldwide."

The New Research

The new research, published in the Science journal, analyzed the outcome of staghorn coral and elkhorn coral 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-forming corals and are named because they look like, in turn, the antlers of male deer and elks.

However, researchers who performed underwater surveys of more than 52,000 colonies of the species, across nearly four hundred sites along Florida's coast, found widespread, often catastrophic, losses.

Regional Effects

• Along 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, mortality rates were reduced, at about 38%.

Past and Current Threats

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

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 expel the symbiotic algae living in their tissues, causing them to become bleached white.

If temperatures remain elevated, the corals die off entirely.

Global Implications

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

This poses a significant danger to:

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

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

Preservation Efforts

In a desperate attempt to avert a decline of threatened corals, scientists have created repositories 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 lost off the state in the last forty years.

But as global heating continues to intensify, there is slim chance of long-term survival of these species absent significant actions, researchers warn.

Additional Researcher Insight

"Elkhorn corals, especially, are some of the key wave-breaking coral species in the area," said Andrew Baker, a ocean scientist at the University of Miami.

"They were once abundant on shallow reef tops in the Caribbean, and if we want our reefs to continue protecting our coastlines from flooding during storms, it is worthwhile taking exceptional steps to ensure we don't lose these corals altogether."