Bleached coral is visible at the Flower Garden Banks National Marine Sanctua

Coral reefs around the world are experiencing global bleaching for the fourth time, top reef scientists declared Monday, a result of warming ocean waters amid human-caused climate change.

Coral reef bleaching across at least 53 countries, territories or local economies has been confirmed from February 2023 to now, scientists from the National Oceanic and Atmospheric Administration and International Coral Reef Initiative said. It happens when stressed coral expel the algae that are their food source and give them their color. If the bleaching is severe and long-lasting, the coral can die.

Coral reefs are important ecosystems that sustain underwater life, protect biodiversity and slow erosion. They also support local economies through tourism.

 

Bleaching has been happening in various regions for some time. In the world’s largest coral reef ecosystem, Australia’s Great Barrier Reef, bleaching affected 90% of the coral assessed in 2022. The Florida Coral Reef, the third-largest, experienced significant bleaching last year.

But in order for bleaching to be declared on a global scale, significant bleaching had to be documented within each of the major ocean basins, including the Atlantic, Pacific, and Indian oceans, in both the Northern and Southern Hemispheres.

Monday’s news marks the second worldwide bleaching event in the last 10 years. The last one ended in May 2017. Brought on by a powerful El Nino climate pattern that heated the world’s oceans, it lasted three years and was determined to be worse than the prior two bleaching events in 2010 and 1998.

This year’s bleaching follows the declaration that 2023 was the hottest year on record.

“As the world’s oceans continue to warm, coral bleaching is becoming more frequent and severe,” Derek Manzello, NOAA Coral Reef Watch coordinator, said in a statement.

Selina Stead, a marine biologist and chief executive of the Australian Institute of Marine Science, called climate change “the biggest threat to coral reefs worldwide.” She said scientists are working to learn more about how coral responds to heat and to identify naturally heat-tolerant corals, but said it is “critical the world works to reduce carbon emissions.”

One reef that fared better than others last year was the Flower Garden Banks National Marine Sanctuary, which was afforded some protection by its location in deeper water in the Gulf of Mexico about 100 miles off the Texas coast. Sanctuary officials didn’t immediately respond to messages Monday seeking the latest on the health of the sanctuary’s corals.

Coral reef bleaching across at least 53 countries, territories or local economies has been confirmed from February 2023 to now, scientists from the National Oceanic and Atmospheric Administration and International Coral Reef Initiative said. It happens when stressed coral expel the algae that are their food source and give them their color. If the bleaching is severe and long-lasting, the coral can die.

The world’s coral reefs do more for the planet than provide underwater beauty.

They buffer shorelines from the effects of hurricanes. An estimated 500 million people earn their livelihoods from the fishing stocks and tourism opportunities reefs provide. The tiny animals that give rise to reefs are even offering hope for new drugs to treat cancer and other diseases.

Despite their importance, warming waters, pollution, ocean acidification, overfishing, and physical destruction are killing coral reefs around the world. Schemes to save those reefs are as creative as they are varied; most recently, scientists released data showing that marine protected areas can help save reefs if they are placed in just the right spots. Genetics is also becoming a larger area of coral research, giving scientists hope they might one day restore reefs with more heat tolerant coral.

But now, in the lead-up to World Oceans Day on June 8, scientists caution that these and other strategies may only buy reefs time until world leaders implement aggressive climate change action.

Without a mix of long-term cuts in emissions and short-term innovation, there’s a not-so-far-off future where coral reefs as we know them simply cease to exist, says Anne Cohen, a coral expert at the Woods Hole Oceanographic Institution in Massachusetts.

Coral reefs are important ecosystems that sustain underwater life, protect biodiversity and slow erosion. They also support local economies through tourism.

In this image provide by NOAA, a fish swims near coral showing signs of bleaching at Cheeca Rocks off the coast of Islamorada, Fla., on July 23, 2023. Reef scientists say coral reefs around the world are experiencing global bleaching for the fourth time due to prolonged warming of the oceans. (Andrew Ibarra/NOAA via AP)
 

In this image provide by NOAA, a fish swims near coral showing signs of bleaching at Cheeca Rocks off the coast of Islamorada, Fla., on July 23, 2023. (Andrew Ibarra/NOAA via AP)

Bleaching has been happening in various regions for some time. In the world’s largest coral reef ecosystem, Australia’s Great Barrier Reef, bleaching affected 90% of the coral assessed in 2022. The Florida Coral Reef, the third-largest, experienced significant bleaching last year.

Monday’s news marks the second worldwide bleaching event in the last 10 years. The last one ended in May 2017. Brought on by a powerful El Nino climate pattern that heated the world’s oceans, it lasted three years and was determined to be worse than the prior two bleaching events in 2010 and 1998.

This year’s bleaching follows the declaration that 2023 was the hottest year on record.

 

“As the world’s oceans continue to warm, coral bleaching is becoming more frequent and severe,” Derek Manzello, NOAA Coral Reef Watch coordinator, said in a statement.

Selina Stead, a marine biologist and chief executive of the Australian Institute of Marine Science, called climate change “the biggest threat to coral reefs worldwide.” She said scientists are working to learn more about how coral responds to heat and to identify naturally heat-tolerant corals, but said it is “critical the world works to reduce carbon emissions.”One reef that fared better than others last year was the Flower Garden Banks National Marine Sanctuary, which was afforded some protection by its location in deeper water in the Gulf of Mexico about 100 miles off the Texas coast. Sanctuary officials didn’t immediately respond to messages Monday seeking the latest on the health of the sanctuary’s corals.

OFF THE COAST OF GALVESTON, Texas (AP) — Divers descending into azure waters far off the Texas coast dip below a horizon dotted with oil and gas platforms into an otherworldly landscape of undersea mountains crusted with yellow, orange and pink coral as far as the eye can see.

Some of the world’s healthiest coral reefs can be found in the Gulf of Mexico, about 100 miles (160 kilometers) off the Texas coast. Sheltered in a deep, cool habitat far from shore, the reefs in the Flower Garden Banks National Marine Sanctuary boast a stunning amount of coral coverage. But scientists say that like all reefs, they are fragile, and their location will only offer protection for so long in the face of a warming climate.

“To see that much coral in one place is really magnificent — an experience that most people don’t get on reefs in this day and age,” said Michelle Johnston, the acting superintendent and research coordinator for the federally protected area.Bleached coral is visible at the Flower Garden Banks National Marine Sanctuary, off the coast of Galveston, Texas, in the Gulf of Mexico, Saturday, Sept. 16, 2023. The sanctuary had some moderate bleaching this year but nothing like the devastation that hit other reefs during the summer's record-breaking heat. (AP Photo/LM Otero)

Bleached coral is visible at the Flower Garden Banks National Marine Sanctuary, off the coast of Galveston, Texas, in the Gulf of Mexico, Saturday, Sept. 16, 2023. (AP Photo/LM Otero)

he sanctuary had some moderate bleaching this year but nothing like the devastation that hit other reefs during the summer’s record-breaking heat. Still, Johnston said that’s among her top concerns for the sanctuary’s future. Waters that get too warm cause corals to expel their colorful algae and turn white. They can survive if temperatures fall but they are left more vulnerable to disease and may eventually die.

Florida’s coral reef — the world’s third-largest — experienced an unprecedented and potentially deadly level of bleaching over the summer. Derek Manzello, coordinator of the National Oceanic and Atmospheric Administration’s Coral Reef Watch, said that so far this year, at least 35 countries and territories across five oceans and seas have experienced mass coral bleaching. He said it’s too early to know how much of Florida’s reefs will recover since coral may die as much as a year or two after the bleaching.

Sanctuary officials say even in the occasional years when Flower Garden Banks has experienced more serious bleaching than this year, it has bounced back quickly thanks to its overall health and depth, and it’s already recovering this year.

A report expected in the coming months will look at the sanctuary’s vulnerability to the projected effects of climate change.

The Flower Garden Banks stands out for its amount of coral cover — an average of over 50 percent across some areas of the sanctuary — compared with around 10 percent cover in the Caribbean and Northwest Atlantic region, Manzello said. Its corals are also about 60 feet (18 meters) below the surface and surrounded by even deeper waters, compared with many reefs where corals are in shallower water just offshore

In the early 1900s, fishermen told of peering into the Gulf’s waters and seeing a colorful display that reminded them of a blooming garden, but it was such an unusual spot so far from shore that scientists making the initial dives in the 1960s were surprised to actually find thriving coral reefs.

An estimated 4,000 fish species, and some 25 percent of marine life, depend on coral reefs at some point in their existence. Fish keep the algae that grow on corals in check, allowing corals to breathe and access sunlight. While an MPA won’t protect corals from heat waves, these natural safe zones can keep fisheries more sustainable in the long term, and fishers around well-managed MPAs often benefit from the “spillover” of healthy fish stocks that populate surrounding waters.

At a talk hosted by the Woods Hole Oceanographic Institution on Wednesday, renowned marine biologist Sylvia Earle promoted the idea of using marine parks to protect coral, which she does through her organization Mission Blue.

“Reefs that have been protected or not yet exploited by fishing impacts survive when nearby places do not,” she says.

recently published assessment of 1,800 reefs in 41 countries found that only 5 percent of reefs were able to provide all of their lucrative byproducts, such as healthy fish stocks and biodiversity. To increase that percentage, new marine reserves will need to be strategically placed in areas well away from humans, say experts. It wouldn’t save all reefs, but it would help ensure that more reefs function at 100 percent of their potential instead of just a fraction, says Alan Friedlander, the chief scientist for National Geographic’s Pristine Seas initiative and an ecologist at the University of Hawaii who helped author the reef assessment.

“Without this protection,” he says, “any technological enhancements will suffer the same fate as natural reefs, since the stresses have not abated.”

Innovation to the (immediate) rescue

Beyond such nature preserves, some conservationists are looking to more hands-on methods. One research center in the Florida Keys is exploring a form of natural selection to keep corals afloat.

The reef system in the Keys has been hit hard by climate change and disease, which is especially tough, because corals there help support fisheries worth an estimated $100 million every year. In addition, corals off Florida’s coasts are polluted by agricultural and sewage runoff.

The additional stress from warming waters is like “the proverbial nail in the coffin,” says Erinn Muller, the science director at the Elizabeth Moore International Center for Coral Reef Research and Restoration at the Mote Marine Laboratory in Sarasota, Florida.

To keep the wild ecosystem alive, Muller and her team are harvesting samples of the corals that have survived the environmental stresses naturally, breeding them by hand, and reattaching them to the reef. At any given time, the center has 46,000 corals growing on underwater plastic lattices in its nursery. So far, the center has regrown over 70,000 corals from five different species on damaged reefs.

“The ultimate goal is we put ourselves out of a job,” says Muller.

In the Bahamas, Ross Cunning, a research biologist at Chicago’s Shedd Aquarium, is focusing on corals with robust genes that could make them natural candidates for restoration projects. He recently published a study of two Bahamian reefs, one that seemed to survive an intense 2015 heat wave, and one that didn’t.

“It sets the stage to find out which genes are responsible for thermal tolerance,” says Cunning, adding that he hopes identifying those genes will help scientists one day breed more heat-tolerant coral.

In Massachusetts, Cohen’s research has found two key elements that seem to protect corals. The first: internal waves beneath the ocean’s surface that bring cooler currents to heat-struck corals, essentially air-conditioning them as temperatures rise. The second: adaptation, a trait that corals found in Palau’s warm lagoons seem to exhibit.

A race against warming

Muller notes that their efforts on the Florida reefs can help keep them from what she describes as “functional extinction.” But she says the reefs ultimately won’t be restored to their potential until their environment becomes more hospitable to their survival.

All the scientists interviewed for this article noted that mitigating climate change is the only long-term, sustainable solution to conserve and restore coral reefs. Despite global lockdowns and sharply falling emissions, atmospheric carbon dioxide still reached a record high in May.

Global warming is “raising the background temperature,” compounding regular heat waves and making them even deadlier for corals, says Kristopher Karnauskas, an atmospheric scientist at the University of Colorado Boulder who recently published a study investigating the physical causes of the 2016 event.

The oceans absorb and store heat very efficiently; as Earth warms, the oceans take in over 90 percent of the planet’s heat trapped in the atmosphere by human-generated greenhouse gases. But their heat-storing capacity isn’t limitless, and excess heat over time takes its toll on ocean inhabitants.

In evolutionary history, corals date back 400 million years, and with each global temperature change Earth has undergone, corals have adapted—but never as quickly as they must today.

“We know that because there have been six major coral reef extinctions in the geologic past where they were basically wiped out. All those have been associated with excessive heat and ocean acidification,” Cohen says. “Coral reefs always come back, but it takes tens of thousands of years.”

Now, with climate change-driven temperatures rising at a rate higher than corals have ever had to naturally adapt to, Cohen says, “we don’t have that kind of time.”

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