- The latest “report card” on Mesoamerica’s coral reefs made clear that 2024’s hottest-ever recorded summer temperatures devastated some of the region’s most iconic reef sites.
- But against all odds, a reef in Tela Bay on Honduras’s Caribbean coast, composed largely of critically endangered elkhorn corals (Acorpora palmata), displays remarkable health.
- Known affectionately as “Cocalito,” this patch of coral is raising urgent questions about what qualities endow coral with heat resilience and whether they can be harnessed to help save other reefs.
TELA BAY, Honduras — Viewed from the boat, the mighty elkhorn corals shimmer through the clear water, their tips grazing the surface and seeming to reach for the hull. But it’s only when one is submerged that the corals display their full size and strength, and all the busy biodiversity swarming around them. Some of the corals are wider than a man is tall, and the white-tipped, antler-like branches of individual corals interlock to create expanses of reef that entirely cover the seafloor, leaving nothing to see but coral. On it stretches across the bay, for more than a kilometer (0.62 miles).
The latest “report card” on Mesoamerica’s coral reefs made clear that 2024’s hottest-ever recorded summer temperatures devastated some of the region’s most iconic reef sites. But against all odds, this reef at the western end of Tela Bay on Honduras’s Caribbean coast, composed largely of critically endangered elkhorn corals (Acropora palmata), displays remarkable health. Known affectionately as “Cocalito,” this patch of coral is raising urgent questions about what qualities endow corals with heat resilience and whether they can be harnessed to help save other reefs.
“The reef challenges our basic understanding of corals, as it is thriving at a time where we are trying to stop reefs from dying,” Paolo Guardiola, a biologist and dive instructor in the town of Tela, told Mongabay. As the area’s program coordinator with the Coral Reef Alliance, a U.S.-based NGO that supports local reef conservation groups, he’s been monitoring the bay’s coral for several years, and contributed to the report card.
Stressors in Tela Bay
Tela Bay isn’t well known as a diving destination. Yet its coral reefs are plentiful and diverse, covering around 68% of the bay. Local divers routinely discover new reefs here, but report that some recent finds were completely or partially dead, with signs of rapid deterioration. In 2023, a wave of mortality swept the bay’s corals, driven by bleaching and stony coral tissue loss disease (SCTLD). The Mesoamerican reef report card notes that Tela was subject to a mass bleaching event in 2024.
“In Tela, monitoring has found that some coral species have been disproportionately affected by the climate conditions compared to others,” Julio San Martín Chicas, Coral Reef Alliance’s program manager for the region, told Mongabay. “It sure was not an easy year for the corals in the bay.”
Increasingly hot summers, supercharged by climate change, are relentlessly harming delicate coral ecosystems. An ongoing global coral bleaching event, the worst on record, began in 2023 and has affected 84% of reefs worldwide. Excess heat leads corals to expel the symbiotic food-producing algae that live in their tissues and give the corals their color, turning the coral white. The process, called bleaching, weakens the coral and can kill it if conditions persist.
In addition to the heat, many other human-caused stressors affect Tela Bay’s corals, and conservationists are keenly aware that reducing them is the best way to help corals withstand the rising temperatures.
“It is our task to mitigate the stress factors and buy valuable time for the corals to adapt,” Guardiola said. “They either adapt or die.”
One such stressor is the periodic flood of pollutants from the Ulua River. The river flows almost entirely across Honduras collecting sediment, fertilizer and chemical waste, which it expels into the bay. “Fertilizer, for example, boosts the growth of algae, which compete for the same nutrients in the ecosystem,” Guardiola said. “If they grow larger, covering the coral, it would deprive them of critical oxygen and effectively choke [the coral].”
Fishing and frequent storms damage corals in the bay. Tourists, too. Ana Gonzales, an environmental educator with the Tela-based NGO AMATELA, said the holiday influx brings boat and Jet Ski traffic, as well as garbage and pollution. She also pointed to the almost weekly unloading of oil tankers in the bay, which happens completely unsupervised. “We have reports of oil spills, but nobody has managed to get out there and check,” she told Mongabay.
Cocalito
Cocalito has no officially registered name; locals refer to the vibrant patch of reef by the same name as the nearby beach.
That’s where Alejandro Andino, one of the region’s first environmental activists, grew up. Andino had a small house in Cocalito before the area was designated a national park, now named for his friend and collaborator, the murdered conservationist Jeannette Kawas. Andino has known the reef intimately since he was a kid, long before the first divers reached the bay.
“It has always retained its beauty, despite all the ugly battles we had to endure to protect this region,” Andino told Mongabay.
The elkhorn coral that comprises most of the Cocalito reef used to be one of the most dominant coral species in the Caribbean, where it lives exclusively. But disease, bleaching and other human-caused stressors have killed up to 98% of the species in some areas since the 1980s, according to the IUCN. In a few places, however, surviving patches have proved to be quite adaptable and heat-resistant. At the Cocalito reef, partially or fully bleached sea fan corals (genus Gorgonia) are scattered among the ultra-healthy elkhorns.
The species is arguably subject to even worse conditions on Cocalito than it is in places where it has lost ground. The shallow waters increase the heat stress on the corals significantly. Meanwhile, the Ulua and other rivers release extreme levels of pollution. Despite simultaneous exposure to these two most critical coral stressors, Cocalito stands tall.
Theories on resilience
Cocalito’s resilience has attracted international academic attention and spawned a multitude of theories that could explain its survival.
Andrew Baker, director of the Coral Reef Futures Lab at the University of Miami in the U.S., spearheaded an expedition to the reef in 2024, supported by local aquarium and dive shop Tela Marine. He and his team hypothesized that the genetic composition of Cocalito’s elkhorns might be responsible for their high level of resilience. The team collected 13 elkhorn colonies for research purposes, three of which they crossed with Floridian elkhorns in hopes of creating a resilient strain capable of repopulating Florida’s dying reefs, where the species is considered “functionally extinct.”
Early studies by Baker’s team show Cocalito’s elkhorn corals “are completely dominated by [an] unusual heat-tolerant symbiont,” Baker told National Geographic, referring to the food-producing algae the corals depend on. However, the results remain unpublished, and Baker told Mongabay there have been no definitive results yet.
“Without the proper research results, we have to accept that the genetic mutation and resilience of the corals themselves is one of many theories that could explain the reef’s mysteriously perfect health,” San Martín Chicas said. “[B]ut there are many other factors involved that could influence the reef’s survivability.”
Cocalito’s location could offer an explanation. The currents that run near it might divert the polluted sediments the Ulua River channels into the bay. Also, these same currents might kick up sand to form a protective layer that shields the corals from the sun.
People might also play a role. Fishers avoid the area due to the shallow waters and high risk of getting their nets entangled in the sturdy corals. This might lead to a greater diversity of marine life that can interact with the corals and boost the nutrient exchange between organisms.
“It is still too early to give definitive answers regarding the unaffected reef, but what we do know is that it is in magnificent shape,” Guardiola said.
Cocalito’s future
Coral conservationists are stepping up their efforts in Tela Bay. AMATELA recently received funding for equipment and transportation from the Mesoamerican Reef Fund (MarFund), which will allow it to independently conduct research, monitoring and conservation activities across the bay. And MarFund is training a new Post-Storm Reef Response Brigade in Tela, whose members will repair reefs damaged by storms.
Cocalito’s resilience inspired an international crew of filmmakers, journalists, scientists and divers to tell the story of what they’re calling the “Rebel Reef,” with production of a documentary and virtual reality experience to begin in the coming months, in collaboration with Tela Marine.
“When I first took a peek at the reef it just blew my mind,” Tiffany Duong, the Florida-based co-founder of the nonprofit behind the project, Tela Coral, told Mongabay. “It felt like the world of coral conservation was full of opportunities again.”
In April, the group announced it had spotted coral disease on the reef, albeit not on the elkhorn. The same month, it announced it had helped purchase land to build a biobank for the Tela Bay’s corals. “We want to show people what we can see down there so they can actually care,” Duong said, “I believe there is a lot Tela can teach us about coral conservation.”
Banner image: Endangered elkhorn coral thrive on the Cocalito reef in Tela Bay. Image by Fritz Pinnow for Mongabay.
Even the Gulf of Aqaba’s ‘supercorals’ bleached during 2024 heat wave
Citation:
Safuan, C. D., Samshuri, M. A., Jaafar, S. N., Tan, C. H., & Bachok, Z. (2021). Physiological response of shallow-water hard coral Acropora digitifera to heat stress via fatty acid composition. Frontiers in Marine Science, 8. doi:10.3389/fmars.2021.715167
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