In Mexico, scientists race to save Marietas Islands’ corals from ocean warming

The corals of the Marietas Islands, a pair of small islands in Mexico’s Pacific Ocean, have survived record-high temperatures and uncontrolled tourism triggered by the sudden international fame of “the beach of love,” a picture-perfect quarry where people like to take selfies.

Today, the corals of Islas Marietas National Park, created in 2005, are recovering slowly, reduced to a fifth of the coverage they had 30 years ago.

In 2016, a government decree put a stop to uncontrolled tourism in the area. But during the second half of 2023, El Niño set back the recovery process. High temperatures brought on by the climate event caused widespread coral bleaching.

Bleaching happens when corals become stressed by pollution, acidification or a rise in ocean temperatures. They expel the tiny algae living inside them providing food. Once that happens, the corals lose their color and die.

But it’s not all bad news, according to Paola Rodríguez Troncoso, coordinator of the University of Guadalajara’s coral rehabilitation project for Mexico’s central Pacific. The marine biologist said more than a decade of work has led to the discovery of individual corals that show resistance to high temperatures. The discovery, she said, could help address the problems brought on by climate change.

Successes and setbacks to recovery

In 1997, when the biodiversity of Las Marietas was hit by a previous El Niño, the biology monitoring program at the University of Guadalajara went to work coming up with a response. They saw that the ecosystems were resisting ocean warming. But the corals were outmatched by the influx of tourists. On Las Marietas — made up of Long Island, Redonda Island and several islets — visits spiked in 2016, according to researcher Amílcar Cupul Magaña.

He said the state of Nayarit used the “the beach of love” on Redonda Island as a centerpiece in its tourism promotion campaigns. The cave sits within a cliff, offering an unusual and irresistible setting for thousands of daily visitors who want to take photos. The area has been marketed as a “must-see” before you die.

“The scale is unmatched,” Magaña said. “If now there are 14,000-20,000 people a year, then before, there were at least 150,000, up to 200,000, just to take photos. Frivolous tourism. Selfies.”

Today, the busiest days see 150 people, but eight years ago the usual daily figure was more than a thousand, he said.

By that point, Las Marietas had already been declared a natural protected area. Research on the wealth and fragility of its biodiversity began in the 1990s, and the Mexican government declared it a national park in 2005. It covers a total area of 53.5 square kilometers (20.6 square miles) and 1,383 hectares (3,417 acres) of emerged surface.

However, the management program came late, in 2011, as did the program for visitor capacity. According to Magaña, coral coverage in 1995 was at around 25% of the island surface but in 2016, it had declined to 10%.

“The impact was so severe that CONANP [National Commission of Protected Natural Areas], responsible for the park, took action on the matter and temporarily closed the site in April 2016.”

Since then, an intensive restoration program has been underway. “We’d begun restoration experiments in 2011. We saw that at four months, the coral attached to the substrate. We used that data as a starting point,” Magaña said.

The park’s reopening didn’t take long, but the new rules changed everything. Visits were reduced by almost 90% and requirements were put in place for use of sunscreen, trash disposal and approaching wildlife. Some parts of the islands have been completely restricted due to their fragile ecosystems and ongoing research projects.

Tourism operators’ response was essential to protecting the islands, said Isaí Pelayo, the former president of Bahía Unida, an NGO. Tourism operators had to understand that limiting tourism was a way of “not killing the goose that lays the golden eggs.”

Scientists planted around 4 million coral fragments and monitored samples. “It showed that 85% survived and grew 4.5-5 centimeters (1.7-2 inches) per year,” Magaña said.

It was a resounding success, even when considering the damage left by Hurricane Roslyn in October 2022. Coral coverage surpassed that of 1995, reaching 28% coverage.

In this part of the Pacific, there aren’t any large coral or barrier reefs, so coral coverage usually reaches 33-35%, according to Troncoso.

But in 2023, the arrival of El Niño was stronger than any in the past, with temperatures reaching 3° Celsius (5.4° Fahrenheit) above the historical average, when at most the anomaly was 1.5°C (2.7°F) in previous events., Troncoso said.

New strategies for fighting climate change

El Niño is the warming phase of a natural climate phenomenon known as El Niño-Southern Oscillation. In 2023, global average sea surface temperatures reached record highs. By the end of the year, more than 90% of the world’s oceans had been hit by heat waves, damaging vital ecosystems and food systems, according to the World Meteorological Organization (WMO).

Experts say it was due to a combination of El Niño and global warming, which was caused by high concentrations of greenhouse gases that reached unprecedented levels in 2022, WMO said.

The coral bleaching that took place in 2023 was “brutal throughout the eastern tropical Pacific, from La Paz in Baja California to the coasts of Colombia. To cite one fact, Huatulco, in Oaxaca, lost 100% in some areas,” Troncoso said.

“In the central Mexican Pacific, with Las Marietas and Isabel Island to the north and Cuastecomate to the south, practically everything between 2 and 20 meters [6.5-66 feet] deep was bleached, with stronger impacts between 2 and 6 m [20 ft],” Magaña said.

Coral is essentially made up of animals, microalgae and microorganisms such as bacteria and fungi. When bleaching occurs, corals shed the colorful algae that live in their tissue, leaving the white skeleton underneath. It leaves them more vulnerable to disease and without their main source of food, resulting in death from starvation, according to the Coral Reef Alliance.

In November 2023, when temperatures started to climb, researchers had to assess the damage. “We had to face the sad reality,” Magaña said. “In Las Marietas, we were left with 4.3% of the surface area covered in corals, less than a fifth of what was recorded in 1995.”

Scientists knew that El Niño was only getting worse, which is why they conducted experiments to prepare a response. “We experimented by creating a deep refuge below 25 m [82 ft],” Troncoso said. The point of the refuge was to plant corals farther away from the light and cushion the effect of increasing temperatures, especially at the surface level and in the first few meters. “The specimens survived well,” he said. “Now we’ve raised them to 10 m [33 ft] and they’ll help us restore damaged areas.”

Additionally, the fact that visits had stopped to areas with coral on Long Island made it possible to carry out a smooth rehabilitation process.

The impact of El Niño “doesn’t mean that we should stop the restoration program but rather look for new evidence-based strategies for how the climate is changing and at what speed,” the scientist said. Along with the refuges, Troncoso said that a nursery program and other techniques are in the works to help the area adapt to new climate conditions.

The corals that survive “have the information, have the genes that have been acclimatized and can be the basis for future populations adapted to an increasingly warmer climate. It’s a step backward but it must also be a step forward,” she said.

More resistant corals

With a changing climate, corals will start adapting structurally to survive, Troncoso said, which is why “we must have the ability to discern what is acclimatizing to those conditions and help them.”

That’s why the restoration team is looking for corals with more resistant genotypes. So far, it’s been successful. “We’ve found not only the animal, per se,” she said, “but also the elements that allow corals to form their calcium carbonate skeleton and three-dimensional structures.”

“We already know the identity of the most resistant symbionts [microalgae]. We know which are the morphotypes [the physical and genetic characteristics] that are associated with these microalgae, and we’ve worked with the bacteria,” the expert said. The next step is to study the role that fungi play in corals.

In Las Marietas, there are four genera of corals: Pocillopora, Pavona, Porites and Psammocora, each with their own morphological differences. There are branched corals, massive corals and crustose corals, among others. However, “We focus on the branched corals for restoration,” Tronocoso said. Specifically, the species capitata, damicornis, verrucosa and eydouxi that belong to the Pocillopora genera.

For this reason, the scientists are interested in making it the centerpiece of the restoration effort.

An ideal restoration project emulates natural conditions, she explained. That’s why they’ve put nurseries in the seabed. “We don’t want to break up the adult colonies, which is why the nurseries are planted in fragments. They grow more quickly because there’s no competition. We leave them there for 6-8 months, then we take them to the natural substrate.” Next May, the researchers will plant the rescued pieces. There will be six nurseries with 70 fragments, all of which will be closely monitored.

The group’s work also involves other areas of the Pacific, including Chamela, Tenacatita and Cuastecomates. Scientists will install six other nurseries and, just like in Las Marietas, search for supportive communities, especially tourism service providers and fishers who can participate in long-term restoration projects.

But Magaña made sure to mention that global ocean temperatures haven’t dropped yet in 2024. Currently, in the most temperate zones, the water temperature is 0.7°C (1.3°F)above average. “It’s not a very encouraging outlook. What we thought was the future has already arrived: frequent bleaching events due to climate change.”

 
Banner image: Coral restoration. Photo courtesy of the University of Guadalajara’s coral rehabilitation project for Mexico’s central Pacific.

 
This story was reported by Mongabay’s Latam team and first published here on our Latam site on Apr. 24, 2024.