Ghost reefs: Florida’s vibrant underwater cities are turning into relics

TAMPA, Fla. (WFLA) — This is the face of climate change in the Florida Keys.

Once colorful coral cities overflowing with marine life are transforming into ghost towns, or rather “ghost reefs,” seemingly overnight.

“We are surprised by the pace. It is unprecedented, what we have seen,” said Scott Atwell, the communications and outreach manager for The Florida Keys National Marine Sanctuary.

“We’ve never seen anything like this. Some are not even bleaching, they are going straight to dead,” Atwell told Nexstar’s WFLA.

“Straight to dead” illustrates just how extreme the marine heatwave is, and how quickly it’s evolving. When under stress, typically coral bleach first, expelling their symbiotic algae partners which give them their vibrant hues, and turn white. Then sometime later, if the heat persists, the coral can succumb and die.

But right now in the Florida Keys, there are reports of rapid mortality. Coral is dropping like dominoes across much of the reef tract from Key Largo to Key West — the third largest tract in the world and the only shallow water reef system in the U.S. mainland.

Although the bleaching and mortality seem to be happening fast, getting to this point has taken about two months. For the past 10-plus weeks, coral has had to endure unusual heat stress. Water temperatures are at record levels in the low 90s along the reef tract, which is several degrees above the normal temperatures in the mid-80s.

Mission: Iconic Reefs, a large-scale NOAA-led coral restoration initiative, reports that the most recent seafloor temperature at Sombrero Key (off Marathon) is 93.4 F and at Looe Key (off Big Pine Key) is 89.6 F. According to Mission: Iconic Reefs, the “optimal” temperature for reef-building corals maxes out at 84 degrees.

Although tropical corals live in warm water, they are very sensitive to just a couple-degree (Fahrenheit) spikes in sea surface temperatures, especially if it lasts for too long. NOAA Coral Reef Watch says at four weeks, coral can begin to show signs of stress. If the heat lasts eight weeks, a bleaching event becomes likely. We are now past the eight-week mark.

Unfortunately, ocean temperatures in the Keys usually peak in late August and early September, so unless there is a major weather pattern shift, this heat stress will likely continue for several more weeks. NOAA Coral Reef Watch has the area under Alert Level 2, the highest alert for bleaching.

Bill Precht is a coral reef scientist in South Florida. In his 45 years studying coral, he’s never been so concerned about the Keys’ iconic reefs.

“If things progress as they have started — record high temps for a record long period — then we are likely seeing a coral bleaching event unlike any other previously observed in Florida. The likelihood of catastrophic levels of mortality are high.”

As a result of this unprecedented event, NOAA Mission: Iconic Reefs and their partner organizations are racing against the clock to rescue coral from the reefs and bring specimens into the lab where they can buy some time until the ocean cools back down.

They are even taking the drastic measure to gene-bank two fragments from each unique genetic individual of staghorn and elkhorn corals, listed as threatened under the Endangered Species Act. In other words, they are preserving the genetic material, so that if much of the coral is lost, there is a way to restore it.

So what are the causes of this prolonged marine heatwave?

Human-caused climate change is one factor. That has elevated the base temperature of the Florida Keys by around two degrees Fahrenheit over the past 50 years. Since corals are very sensitive to a couple of degrees of fluctuation, that is significant.

A study published last year shows that marine heatwaves are increasing in South Florida. In 1980, the area averaged around one marine heatwave per year. The linear trend through 2021 shows an increase to five per year, but in the last several years there’s been an acceleration, now up to eight marine heatwaves per year.

And it’s not just the Florida Keys experiencing unusual ocean heat right now. At the present moment, an astonishing 45% of Earth is covered in marine heatwaves, when normally it would be 10% or less.

While human-forced heating is responsible for some of this heat, the rest can be blamed on the weather. Most marine heatwaves come and go based on weather patterns and wind, or lack thereof.

Since the end of spring, the weather pattern in South Florida has played an integral role in its marine heatwave. This summer, Florida has experienced a very odd weather pattern, where the typical Atlantic high pressure did not nose its way into Florida and the easterly winds did not materialize (until now). The result has been a stagnant weather pattern for weeks with light winds. That has spiked ocean temperatures and not allowed for cooling breaks.

When you combine a favorable weather pattern for ocean warming, on top of the long-term trend of rising ocean temperatures, the result is more frequent and intense heatwaves and growing coral mortality.

There is some good news, though. The season’s first tropical wave is moving in. With it comes rain and breezes. On Wednesday, sea surface temperatures in Florida Bay were 10 degrees lower than Tuesday due to clouds, rain and wind. Shallow water temps can change fast.

But it should be noted the bay is not where the coral reefs are. The 101-temperature reading on Monday was not on the reef tract and has no impact on the coral.

The reef exists on the south side of the Florida Keys, adjacent to deeper water and stronger ocean currents. Therefore the temperatures there are not as hot, but will drop less and take longer to do so. Still, this change in weather pattern is promising, especially if it can continue for a couple of weeks.

But even before this latest bleaching episode, only 3% of coral cover is left in the Florida Keys (down from 40% in the 1970s). That’s due to multiple stressors such as coral disease, nutrient pollution and bleaching. As a result, science has been forced to turn to coral restoration to try to safeguard what’s left and restock the reefs.

For several years now, there have been multiple restoration efforts by the University of South Florida, the University of Miami, Mote Marine, NOAA and many more, including Coral Restoration Foundation in Tavernier.

In an email to WFLA, Dr. R. Scott Winters of the Coral Restoration Foundation said he and his team led a mission to Sombrero Reef last week to collect and safeguard tissue samples from three founder colonies of elkhorn.

“Unfortunately, it was too late,” Winters said. “Our planted colonies as well as wild colonies were affected by the high water temperatures.”

When asked if coral restoration efforts could outpace climate warming, Winters said the team was “optimistic.”

“We know that lots of things can influence a coral’s survival under such stressful events; things like its genetics, environmental conditions, the local environment where it lives, and the reef community it is part of,” explained Winters. “What is clear is that we have to increase the speed and scale of our work so that we can test many different combinations of these factors and see what works in different scenarios.

“There is no magic bullet, or super-coral if you will. Just hard, repetitive work to figure out the combination of pieces that might help coral survive under changing conditions, regardless of what those conditions may be.”

But Winters admits that as the climate continues to warm, coral faces an uphill battle to survive.

“As longterm water temperatures increase in certain areas, no coral may survive,” he said.

“The best we can do — and what we’re working diligently towards — is ensuring that corals will be around tomorrow with the greatest potential for resiliency to adapt to changing conditions, whatever they may be. Coral restoration alone is insufficient to ensure coral reefs exist in the future, but is as necessary component of the plan as is addressing climate change.”  

Climate scientists project that global heating will likely kill 99% of tropical corals around the planet by mid-century. If so, coral reefs will be the first global ecosystem to succumb to climate change.

The only thing standing in the way of Earth’s remaining coral reefs transitioning to “ghost reefs” is humanity’s desire, or lack thereof, to stop the self-inflicted warming.