Unprecedented Coral Bleaching Disaster Unfolding Along Florida's Coast

Coral reefs off the coast of Florida are experiencing a massive coral bleaching event triggered by climate change and the record temperatures that the planet has experienced this summer.

A panel of scientists from the National Oceanic and Atmospheric Administration (NOAA) described the currently unfolding bleaching event, which involves vast swaths of coral reefs experiencing severe bleaching and mortality, as "sobering" and "alarming."

“We hear the word unprecedented thrown around all the time. But allow me to qualify that word with the facts,” Derek Manzello, Ph.D., coordinator of NOAA’s Coral Reef Watch Program, said. “First, Florida’s corals have never been exposed to this magnitude of heat stress. Second, this heat occurred earlier [in the year] than ever before.”

During a recent hour-long call with members of the media, Manzello and several other experts shared their concern about the damage that has already occurred and sought to put the disastrous bleaching event into context.

And while the focus of the media call was primarily the situation off the coast of Florida (at what represents one of the nation’s largest coral reefs), NOAA experts said reefs well beyond The Sunshine State are experiencing record levels of bleaching damage, as well.

"There is a large-scale heat stress and coral bleaching event underway spanning two ocean basins and multiple countries," said Manzello. "The surface temperatures in the Atlantic are currently as high or higher than they've ever been in the satellite record, and heat stress has accumulated earlier than ever before."

The Importance of Coral Reefs

Coral reefs around the world serve a variety of critical functions. They are of vital importance to both human communities and also to the natural environment.

“Teeming with diverse marine life, coral reefs provide nurseries for valuable fisheries that feed millions and provide jobs to those in our coastal communities," explained Steve Thur, Ph.D, NOAA’s assistant administrator for oceanic and atmospheric research. "They draw tourists to boost our economy. They’re important to the cultural heritage of communities on our coast, and they protect coastal areas by reducing the power of waves hitting the coast during hurricanes and severe storms."

Coral reefs also happen to be on the front lines of climate change, serving as a barometer for the fallout of the warming planet and visibly suffering intense devastation as warming occurs.

The bleaching event taking place in Florida is located mostly within the Florida Keys National Marine Sanctuary. The sanctuary is home to the Florida Reef, which is the only barrier coral reef in all of the United States and North America and the third-largest coral barrier reef worldwide.

“The Florida Keys National Marine Sanctuary covers an area of about 3,800 square miles and it extends 180 miles from the Biscayne Bay south of Miami to the Dry Tortugas,” explained Andy Bruckner, Ph.D., director of Coral Reef CPR.

The reef is also home to a diverse community of underwater habitats, including the largest documented contiguous seagrass community in the Northern Hemisphere and more than 6,000 animal species.

Bleached Mountainous Star Coral off the coast of Florida as of July 31st, 2023 (Photo Credit: Courtesy NOAA)

Waters Warming Months Earlier Than Ever Before

The bleaching event now taking place at a once vibrant coral reef has been unsettling for those who have spent years dedicated to its protection and preservation. Heat stress has impacted Florida's coral reefs earlier than ever this year, said Manzello. And that’s due to non-stop soaring temperatures.

"Daily average temperatures have been record setting," Manzello explained. "In the Florida Keys, sea temperatures broke the previous record for the highest value ever measured by satellite on July 9th, and temperatures have been higher than the prior records for 28 of the past 37 days."

Those temperatures in turn, caused the Southeast Florida reefs to reach what’s known as Alert Level 2 conditions, which causes the most extreme heat stress for coral reefs. In fact, all of the Florida Keys and most of southeast Florida are now experiencing Alert level 2 conditions. These types of conditions are known to cause severe bleaching and often, coral mortality.

To put that into some context, during the past eight mass coral bleaching events that have impacted the Florida Keys since 1987, temperatures did not reach this level of heat stress. Furthermore, bleaching wasn’t observed in any of those cases until mid-August.

The current bleaching event, by contrast, began in early July. On July 5 of this summer, the water temperature alert level reached a Level 1, during which heat stress is known to elicit significant coral bleaching. And by July 16, water temperatures had reached an alert Level 2, or mortality level. That means the current bleaching event began five to six weeks earlier than the previous eight mass bleaching events in Florida's history.

“This is a very serious event,” Manzello said, adding: “It’s clear that the accumulation of heat stress started earlier than ever before on record.”

Not only are temperatures reaching and exceeding seasonal peaks far earlier than they have historically—but the warmest months of the year are not even over yet.

The bottom line? Coral reefs are experiencing heat stress that's not only higher than ever before, and earlier than ever before, but it's likely to last for longer than ever before, said Manzello.

What's more, the damage that's occurring is taking place rapidly amid record global temperatures. On June 30th, for instance, Florida's reefs were still healthy, full of vibrant color and beautiful corals. 

"And roughly three weeks later, on July 24th...it's an entirely different scene. So much bleaching, so much paling," said Ian Enochs, Ph.D.

Florida is the Tip of the Iceberg

Yet another message NOAA scientists sought to get across during the recent media briefing is that the reefs off the coast of Florida are not the only location where such unprecedented bleaching is being witnessed. It’s just one of many locations. The planet’s record temperatures are also impacting coral reefs in both the eastern tropical Pacific and the Atlantic oceans.

“Large areas of the Eastern tropical Pacific have experienced alert level 2 conditions,” said Manzello, who shared an image of a completely bleached reef off of the Mexican Pacific, which had been impacted by multi-year temperature increases.

A reef in Bocas del Toro, in Panama, served as another example of the impacts of global warming on coral reefs. Severe bleaching began showing up at the Bocas del Toro site in early July. The images shared with the media showed threatened species of coral that had recently experienced heat-driven mortality.

These types of examples are numerous. While Florida may be experiencing the worst of the current bleaching event, there are plenty of other locations that are currently dealing with extreme conditions as well.

“We have confirmed bleaching in five countries bordering the Eastern Pacific, off Mexico, El Salvador, Costa Rica, Panama, and Columbia,” Manzello said. “In the Atlantic there is confirmed bleaching in at least seven countries and territories. That includes Florida, both sides of the Yucatan Peninsula off Mexico, Belize, Cuba, Panama, Puerto Rico, and the US Virgin Island.”

The widespread bleaching started in the Eastern Tropical Pacific in early June and there are now confirmed reports of severe bleaching from southern Mexico around Oaxaca all the way down through Columbia.

"So we're talking about thousands of miles of bleaching-level heat stress with confirmed bleaching reports," said Manzello.

Beyond Coral Reefs

Off of Southern Mexico, near the Oaxaca area, not only are corals severely bleached, but scientists are also witnessing entire ecosystems being impacted by heat stress. In particular, sharks, an apex predator critical to a healthy ecosystem, have disappeared entirely from the area.

NOAA scientists on the recent media call attributed this to the lack of nutrients in the surface waters amid global warming.

“You have very low nutrients in the surface waters, and productivity goes way down. So the food sources for the sharks are going away. And also we need to consider the fact that when waters are warmer, there's less oxygen,” explained Manzello. “The sharks, as we know, always need to be swimming around constantly because they have a high oxygen demand. So essentially what you have is a situation where sharks have moved out these areas in the Mexican Pacific because it's basically just too hot for them.”

Future Outlook

NOAA’s Coral Reef Watch monitors heat stress in near real time and also produces a four-month coral bleaching outlook. This forecast is model-based and utilizes NOAA's climate forecast system
to provide weekly updates about possible future heat stress. This outlook currently predicts that the Caribbean will continue to warm for the foreseeable future, enough that the majority of the Caribbean is predicted to experience alert level 2 conditions within the next one to two weeks and they will persist through October.

In Florida’s case, the heat stress is not expected to dissipate until mid- to late- September or early October, as well. That means an area already experience mass mortality, may be looking at an additional month of heat stress.

“Unfortunately, Florida appears to be the location that’s being the most severely impacted by this
large-scale marine heatwave,” said Manzello. “Pretty much every coral in Florida is experiencing alert level 2 conditions. Some sites in the Florida Keys are experiencing accumulated heat stress that’s two times greater than when we expect mortality to begin. Unless we have significant changes in weather patterns and development of tropical storms and hurricanes, we are marching towards a Caribbean-wide heat stress event within a matter of days to weeks.”

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