Even Deep Texas Coast Reefs Aren’t Safe from Coral Bleaching as World’s Oceans Cook

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Some of the healthiest coral reefs on the planet exist off the coast of Texas and Louisiana. But researchers say the Flower Garden Banks National Marine Sanctuary is no longer beyond the reach of fossil fuels and the extreme ocean heatwaves they are causing.

Melissa Gaskill

In 1997, the first documented global coral bleaching event killed at least 15 percent of reefs in tropical basins of the Atlantic, Pacific, and Indian Oceans. A second global event hit in 2010. And another in mid-2014. That one lasted until July 2017 and affected 70 percent of the world’s reefs, even some that had never bleached before, including the northernmost Great Barrier Reef of Australia.

With ocean heat blowing past all historic records in 2023, the National Oceanic and Atmospheric Administration (NOAA) announced that a fourth global coral bleaching event was underway, with mass coral bleaching reports starting in February 2023 and continuing into 2024.

“As the world’s oceans continue to warm, coral bleaching is becoming more frequent and severe,” Derek Manzello, NOAA’s Coral Reef Watch coordinator, said in an April press release. “When these events are sufficiently severe or prolonged, they can cause coral mortality, which hurts the people who depend on the coral reefs for their livelihoods.”

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Scientists still are assessing the damages but generally expect them to be worse than the last bleaching event and to impact every ocean basin on Earth. The heat has been such that even the relatively deep reefs at the Flower Garden Banks National Marine Sanctuary in the Gulf of Mexico are being impacted.

The ocean absorbs 90 percent of the heat created by carbon emissions from burning fossil fuels. “Bleaching” is a coral response to the hotter water temperatures that result.

Reefs are made of thousands of tiny organisms, called polyps, that create hard external skeletons connected into massive communities. Polyps have algae living in their tissues that provide most of the coral’s nutrition through photosynthesis.

Polyps become stressed in high water temperatures, sometimes to the point that they kick out these colorful algae, leaving the coral looking white or bleached. Unless water temperatures drop to normal ranges and a polyp takes its algae back in, it will eventually starve and die.

In the 160-sqaure mile Flower Garden Banks National Marine Sanctuary, roughly 100 miles from the Texas coast, tropical coral reefs grow atop ancient salt dome formations. These reefs are at least 10,000 years old, likely started by coral polyps that drifted here on currents from the Yucatan peninsula.

Its distance from land and location deeper than most tropical reefs have largely protected these reefs from threats ravaging those in Florida, the Caribbean, and the rest of the world. Living coral cover remains above 50 percent here, versus about 10 percent in Florida, where research teams have responded to recent bleaching events with significant restoration efforts.

But one of the world’s longest-running scientific monitoring programs, begun in 1978, has documented that even these reefs have begun to feel the heat. In 2016, for example, 24 percent of corals at the East Bank and 10 percent at the West bleached. In 2022, scientists warned that sea-surface temperatures in the Gulf of Mexico will surpass critical bleaching thresholds by mid-century without substantial mitigation of climate change.

Late last year, the Flower Garden Banks reefs experienced “moderate” bleaching. That’s a problem because in a world where reefs are under such stress it’s places like Flower Garden Banks that could “serve as the repositories for what could help restore some other reef potentially in the future,” Kelly Drinnen, NOAA education and outreach specialist for the Flower Garden Banks, told the Associated Press.

The sanctuary is expected to be under watch for another potential bleaching event that may arrive in two to three months time.

The monitoring program at Flower Garden Banks collects data on coral cover and core components on the health of the ecosystem, NOAA research specialist Marissa Nuttall told Deceleration. The data provide an important historical record that helps researchers see the effects of natural and human-caused events, including ever-warmer ocean waters that lead to bleaching.

“Our focus is on monitoring resources so we can see and maybe get ahead of declines or tipping points,” Nuttall said.

These reefs also are affected by pollution and storm run-off from the Mississippi River watershed, which drains 41 percent of the continental U.S.—parts of 31 states—into the Gulf of Mexico. Coastal flooding from severe storms in 2016 and 2017 stressed or killed reef corals, sponges, and small bottom-dwelling creatures such as such as worms and crustaceans up to 115 miles offshore—including at the Flower Gardens.

And those currents that first brought coral polyps here now can bring pathogens that cause disease from other parts of the Gulf and beyond. That is particularly bad news given that warming oceans create a higher risk of infectious outbreaks, especially for corals.

In fact, during a monitoring cruise in August 2022, scientists observed lesions—white patches of dead coral tissue—on brain and star corals at the East and West Banks that resembled stony coral tissue loss disease (SCTLD). Discovered near Miami in 2014, this disease has spread throughout Florida’s reef, affecting more than 20 species of reef-building corals there, killing many of them within weeks or months.

Flower Gardens staff had developed a disease response plan, Nuttall says, and following the early observations, put the plan into action. That included surveying more reefs to see how widespread the disease was, collecting samples to try and identify it, and applying antibiotics to the lesions. Early analysis suggests that the outbreak may not be SCTLD but a new disease. Fortunately, it seems to no longer be active.

[UPDATE (May 16, 2024): NOAA staff report today that the damage was not caused by SCTLD but white plague disease, which is considered neither as lethal nor as fast-spreading as SCTLD.]

Ocean currents also bring invasive species. Lionfish, an invader from the Indo-Pacific, first was seen in Florida waters in 1985 and by 2014 had established themselves across the entire U.S. Atlantic Coast, Caribbean, and Gulf of Mexico. First observed in the Flower Gardens in 2010, they were well-established throughout the Sanctuary by 2012.

In addition to monitoring these venomous fish, Sanctuary staff sponsor Lionfish Invitationals where volunteer divers actively remove them.

“While lionfish have been bad for the sanctuary, they have been an unexpected unifier, increasing awareness about the Sanctuary and bringing a lot of people out to help with the removals,” Nuttall says.

Using satellite tags to track the movements of different animals has become a key component of Sanctuary monitoring. One type of satellite tag must be out of the water to transmit data and is used on animals that frequently break the surface, such as hammerhead sharks. Another type, used on animals that do not break the surface, releases at a pre-determined time and pops to the surface to transmit data.

In 2022, scientists added acoustic tags to their tool box. These do not have to surface, but transmit data to underwater receivers. An array of these receivers was installed in and around the Flower Gardens for a study led by Texas A&M University-Galveston and involving researchers from five universities. The effort was spawned by a study that used 225 underwater acoustic receivers around the U.S. Virgin Islands and southeastern Puerto Rico, finding that fish travel farther and faster than previously thought and spend time in multiple marine protected areas.

Jay Rooker, a professor at TAMU-Galveston’s Department of Marine Fisheries involved in the research, said in a statement:

“We will study a wide range of reef-associated fishes—including groupers, snappers, jacks, parrotfish and sharks—to determine their required habitats and how natural banks within the sanctuary are interconnected.”

Amberjack fitted with the acoustic tags already have been detected traveling throughout the sanctuary, rather than hanging out at one specific bank.

“Our tagging project is making lots of incredible and interesting connections,” Nuttall says. “A cool extra is seeing how the Sanctuary is connected to the larger ocean. We have detected white sharks inside the Sanctuary that have come from the Atlantic, as far away as Nova Scotia. These are sharks that were tagged elsewhere but detected here.

“We’ve seen that the Stellwagen Bank (National Marine Sanctuary, near Cape Cod), Gray’s Reef (National Marine Sanctuary, off the Georgia Coast), Florida Keys, and Flower Garden Banks National Marine Sanctuaries all are connected.”

The acoustic receivers are just one way the Sanctuary monitoring program has evolved, she added.

“The initial program was a much smaller version of today’s. We have a better understanding of what we really need to monitor, such as water temperature to anticipate impacts from climate change and perhaps step in with intervention measures. A lot of the work is focused on managing our resources.”

Those resources have significant economic value. Coral reefs support tourism and commercial and recreational fishing industries, and provide a variety of ecosystem goods and services. The annual value of these services globally is $11 trillion.

But the Sanctuary’s remoteness means that few people ever see it, which is a challenge for those working to protect it.

“If people don’t know about the place and the resources, it is hard for them to care,” Nuttall told Deceleration. “We’re so far offshore that it is hard for people to connect.”

The staff tries to counter that with education and outreach efforts, and in the coming years, NOAA plans to open visitor centers to engage with and educate people about marine sanctuaries.

The biggest challenge looking forward, though, is climate change.

“Our resources are facing a huge threat from changing climate,” says Nuttall. “We have to shift our management focus more to intervention to preserve our biodiversity.

“So far, this remains the healthiest coral reef ecosystem in the continental US, and it is a spot we still have a lot of hope of preserving.”

Unless substantial progress can be made in reducing the emissions driving climate change, though, that hope may be misplaced, even in this remote spot.

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Melissa Gaskill is a native Texan and Austin-based freelance science writer who frequently covers environmental issues, the oceans, and wildlife.

Additional reporting by Greg Harman.

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