Island of Coral Resilience Shows Hope – and Limits – for Reefs’ Future

Bermuda is home to one of the highest-latitude coral reefs in the world, and scientists there are working to decode the keys to its health as climate change devastates reefs elsewhere.

Written by Jessica Leber Published on Read time Approx. 7 minutes
Aerial view of Bermuda, looking from the south.Bettmann/Getty Images

ST. GEORGE’S, Bermuda – In 2014, leading coral scientists put out a blunt report: reefs in the Caribbean were in such bad shape they were at risk of vanishing within two decades. And that was before the most recent global coral-bleaching crisis hit the region hard in 2015.

As the Caribbean’s reefs were dying, some 1,000 miles to the north in the middle of the Atlantic Ocean, scientists in Bermuda were on edge. They were receiving sea temperature reports that could spell trouble for the tiny island’s reefs.

But no worry was necessary, it turned out. Bermuda’s reefs experienced little bleaching. In fact, the northernmost reef in the Atlantic Ocean is still among the healthiest in the wider Caribbean region.

“We typically are reprieved from some of the big global issues around coral bleaching,” said Samantha de Putron, a marine biologist at the Bermuda Institute of Ocean Sciences (BIOS). “We go out and see some of the corals starting to go, and then typically, it’ll be two weeks and the temperatures naturally come down.”

Today, Bermuda’s reefs are still going strong – reason for hope given the continuing global coral catastrophe, BIOS president William B. Curry told an international ocean conference held on the island in May.

“I don’t want people to walk away thinking we don’t have to do anything because everything’s OK here – because the threats are still there – but there’s no doubt that there are reasons to be optimistic based on what we see in Bermuda,” he said.

De Putron said the strong local coral health has energized coral research at BIOS, a more than 100-year-old nonprofit institute that draws researchers from around the world because of its mid-ocean location and long-term data sets of marine conditions in the Atlantic. “Our coral cover has remained remarkably stable,” she said. “That’s put us on the map, research-wise. Why are the corals here so apparently healthy compared to anywhere else?”

She and several of her colleagues are trying to untangle the question and understand what the future of Bermuda’s corals holds. The answers could help scientists and conservationists better understand the survival chances of more vulnerable reefs of the Caribbean to the south.

BIOS scientist Gretchen Goodbody-Gringley explores Bermuda’s deep reefs. (Courtesy of BIOS)

Bermuda, a British Overseas Territory settled just two years after Jamestown, Virginia, is a historic and picturesque island that lies roughly parallel with North Carolina. Buildings and forts dating back more than three centuries along the narrow streets of St. George’s, a United Nations World Heritage site just down the road from the BIOS’s small campus.

But Bermuda’s corals are much older. The only coral atoll in the Atlantic Ocean, the entire island formed as sea level fell during the Ice Age, exposing limestone layers built up by corals along the submerged rim of an extinct volcano. Thanks to the moderating effects of warm Gulf Stream currents, coral species survive to this day. According to one study, the reefs contribute an estimated $722 million a year to the economy, largely through tourism and in coastal protection value. Still, the island’s corals are more known for their role in the area’s famed shipwrecks – Shakespeare’s “The Tempest” was based on a Spanish ship saved from sinking by grounding on the Bermuda reef – than as vibrant scuba diving attractions in their own right.

Like some other so-called high-latitude reefs in the Northern and Southern hemispheres, the reefs are also known for their hardiness.

Winter sea temperatures can drop down to as low as 16C (61F), a couple of degrees below the normal limits for coral survival, but they also rise as high as 30C (86F) in the summer. Bleaching – when stressed corals expel their symbiotic algae – can occur when corals are exposed to prolonged warm temperatures as little as 1 degree C above their usual maximum range. While some minor bleaching has occurred in Bermuda over the last two decades, it has not been extensive and damaged corals have largely bounced back.

View of Bermuda acquired by NASA’s ASTER satellite, with reef platform visible. (NASA/METI/AIST/Japan Space Systems, and U.S./Japan ASTER Science Team)

The island’s coral reefs, which can be seen from the air through crystal clear blue water, are also a great laboratory for scientists simply because they remain relatively untouched by development. Though the narrow, crescent-shaped island is densely populated, Bermuda has few sources of industrial pollution and corals face less fishing pressure than those in the Caribbean.

But Samia Sarkis, executive director of the Bermuda-based Living Reefs Foundation, says damaging human activities are increasing, such as boats running aground on reefs (the island, a famous tax shelter, is a haven for the wealthy yacht-owning class). That’s why her group, which aims to raise funding and awareness around coral restoration, is working with a local hotel to replant more corals. Support to develop local coral restoration projects and methods have been lacking, she said.

Still, overall, scientists generally applaud the Bermuda government’s relatively progressive conservation policies that have created protections for coral ecosystems. The government, for instance, banned large wire mesh traps called fish pots in 1990 after reef fish populations – which are key to maintaining healthy coral – dropped dangerously low. Neither have Bermuda’s corals been devastated by diseases that have spread throughout the Caribbean and Florida. The 2014 report on the region’s reefs called out the Bermuda reef’s “extraordinary resilience” to hurricanes – likely due to their health.

When reef ecologist Gretchen Goodbody-Gringley first came to Bermuda, she was more interested in how corals have survived at all in such a remote, “marginal” location in the first place. She began by studying when and how coral larvae arrived: Her genetic research has shown some coral species regularly migrate to Bermuda from the Caribbean while other species arrived long ago and have been mostly isolated since.

“It’s this initial inhabiting population that’s really evolved to tolerate the conditions in Bermuda,” she said. “That led to questions of their capacity to adapt or acclimatize.”

Ongoing and new research projects at BIOS are testing the limits of Bermuda’s coral resilience at both the lower and upper ends of their temperature range. In Bermuda and Panama, Goodbody-Gringley said she is now comparing how two species – one that has also suffered heavily from bleaching in the Caribbean and one that hasn’t – respond to high water temperatures. The goal is to understand how the corals’ life history affects their ability to withstand heat in different locales.

The bigger idea, which has been supported with data from other high-latitude reefs around the world, is that Bermuda’s corals may be well adapted not just to cold waters, but to a wider temperature ranges and therefore will be more resilient to climate change.

“Fifteen degrees Celsius throughout the year is a lot of fluctuation. A lot of the corals in the central Caribbean are much more sensitive,” Goodbody-Gringley said.

Working with a colleague from the University of Rhode Island, she and de Putron are also now setting up a three-year experiment in large outdoor tanks to test the genetic capacity of corals to adapt to warm conditions – a field of research called epigenetics. The experiment will help determine if local corals can vary their gene expression in response to stressful temperatures and whether useful changes are passed down to the next generation.

That capacity has already been shown elsewhere in a the world. If genetic adaptations are passed down – if corals can “learn” to adjust to their new warmer environment – it would be good news for coral conservation in the region, said de Putron.

Such prospects give her cause for hope. But they also show how scientists don’t yet understand whether Bermuda’s current coral health is because of some built-in capacity to withstand a wide range of temperatures. An alternative explanation is simply that reefs here are just as vulnerable, but just haven’t yet experienced warming or stress to the degree that corals in the Caribbean have.

And even if it turns out Bermuda corals are especially resilient, that could spell sad news for the rest of the Caribbean.

Bermuda’s reefs are the northernmost in the Atlantic Ocean. (Photo Credit: Stacy Peltier)

While Bermuda’s corals create rich ecosystems, they don’t boast the same level of diversity as more tropical locales. Whereas the Caribbean is home to more than 70 coral species, Bermuda has about 30 species, lacking the iconic elkhorn and staghorn corals that provide complex habitats for marine life. Those species have been virtually wiped out in Florida and the Caribbean by bleaching, disease and pollution.

Claire Ross is a PhD candidate at the University of Western Australia who is studying the adaptability of another high-latitude reef in southern Bremer Bay on the country’s southwest coast. She noted there are big differences in the response to changing environmental conditions by massive corals – the boulder-like structures typically found in Bermuda – and the more delicate and faster-growing branching and plating species. These latter species, in the Caribbean, make up the more complex and rich habitat area in reefs, providing hiding places and homes for fish and invertebrates.

“One thought is that it might be that reefs may be transformed a bit into these massive coral communities,” Ross said. “I think that’s a really interesting point to start thinking about. It’s not just where corals are but the species that are there.”

That worries Goodbody-Gringley. “One theory is that…the community that we have here may reflect what the broader Caribbean might look like in the future,” she said. As someone who fell in love with the ocean while diving on vivid and then-healthy reefs in Florida when she was 15, she added: “That would be a loss.”

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