Marine biologist Anastazia Banaszak works to revive coral reefs. She knows all too well that the window for such efforts is closing.

“Most scientists believe that if we don’t control CO2 emissions, the world’s reefs will have disappeared by 2050,” says Banaszak, an Australian-born research professor at the National Autonomous University of Mexico (UNAM). “When you put it in the perspective of our work with coral reef reproduction, that means we have 10 spawning seasons left. That scares me.”

Corals spawn one, maybe two summer nights a year following a full moon. Scientists work through the night to seize the moment. Using specialized nets, they collect the best samples to work with for the rest of the year.

Banaszak heads a team of 12 research technicians and students at the Institute of Marine Sciences and Limnology at UNAM’s campus in Puerto Morelos, 25 miles (40 kms) south of the Caribbean resort city of Cancún. The team is growing and planting new corals while simultaneously creating a coral bank that will enable future restoration work along the Mesoamerican Reef, the world’s second largest barrier reef.

“Cryopreservation is critical because if we lose the coral in the wild, the bank will offer the possibility of reintroducing new corals into the wild, but that means acting now,” says Banaszak, who is also Recording Secretary for the International Coral Reef Society, an association that promotes the dissemination of science on coral reef conservation. “If we wait until 2050, all the coral will be gone.”

Relying on funding from public and private sources, the team so far has banked six of the approximately 60 coral species in the Mesoamerican Reef system, which extends almost 700 miles (1,127 kms) from Isla Contoy, off the northeast coast of Quintana Roo state, Mexico, to the Bay Islands in Honduras. Says Banaszak: “It is a slow and expensive process so we are focusing on the most important and vulnerable species we can find.”

High on the priority list are 23 species already seriously endangered by stony coral tissue loss disease (SCTLD), a rapidly spreading but little-understood disease first reported off the southeast coast of the U.S. state of Florida in 2014. (See "Region’s stony corals face pandemic of their own" —EcoAméricas, March 2021.)

Most reef restoration work around the world relies on a process known as fragmentation, in which coral is broken off the mother colony and propagated, much like a plant cutting. Banaszak and her team are pursuing a different method in Mexico. “We take sperm and eggs and produce new colonies,” she says. “Every coral we produce is a genetically unique individual. Collecting gametes means we can outplant lots of genetically diverse individuals and nature can select the best ones.”

Fertilization vs. fragmentation
While fragmentation is cheaper and quicker, it involves damaging the mother coral, thereby increasing the possibility of infection from disease. It also creates organisms that are less adaptable to changes in their environment because they lack the genetic diversity that the fertilization method can bring.

A one-year-old coral is the size of a large coin. The challenge is to find the ideal timing and conditions for the outplanting stage so the organisms thrive. “The strategy is for populations to be self-producing so we don’t have to keep restoring,” Banaszak says. “So much of the reef is affected by degradation that the challenge is not just knowing what to do, but knowing how to scale up. We can’t just restore one reef; we need to restore the whole system.”

So far Banaszak’s team has planted the equivalent of half a hectare (1.2 acres) along four different reefs in the Mexican section of the Mesoamerican Reef system. “Most of the nations with reefs are low-income, so we don’t just need to scale up, we also need to develop low-cost methods so anyone who wants to work on this can afford to,” Banaszak adds.

So far the technique is being replicated in Belize, Cuba, the Dominican Republic, Colombia and Honduras with scientists from 17 countries having received training in the method at Banaszak’s laboratory. Independently of Mexico’s work, Australia, the United States, Curaçao, Israel, Japan and the Philippines also operate coral-restoration programs that are using and developing fertilization techniques.

Banaszak notes that at least 90% of the Mesoamerican Reef’s coral cover has disappeared. Although there are multiple causes, global warming is considered the greatest single driver. She adds: “If a thermal stress event is brief, the coral might survive it. But if the temperature stress lasts seven, eight or more days, then coral that is not getting its normal food will start to suffer and die.”

The optimal temperature for Caribbean corals is 27 degrees Celsius, or 80.6 degrees Fahrenheit, which was once the norm in the region. Nowadays Caribbean waters can reach temperatures of over 31 Celsius, or 87.8 Fahrenheit, in the warm season.

Spread of sargassum
Compounding coral loss in the Caribbean is a marked decline in water quality. This has contributed to the proliferation of sargassum seaweed in the region’s once-crystalline waters and on its white-sand beaches. Sargassum is a macroalgae that blooms in a warm, nutrient-rich environment. As tourism has grown exponentially along the Caribbean coast, inadequate treatment and disposal of sewage and other waste have caused nutrient pollution. Increased agricultural runoff has contributed, too—a problem exacerbated by deforestation.

Coral grows best in nutrient-poor water thanks to its symbiotic association with the microalgae that help to feed it. By contrast, floating macroalgae blooms, which can extend for thousands of miles, weaken the coral’s defenses and affect its reproductive strength. “Instead of reefs being dominated by corals, they are now becoming dominated by other types of macroalgae that live on the reef substrate and compete with coral,” Banaszak says.

Reefs elsewhere in Mexico also are drawing concern. In December, Guillermo Horta Puga, a UNAM geochemist, reported coral cover in the Veracruz Coral Reef System, which is located in the Gulf of Mexico and is not part of the Mesoamerican Reef, has declined 40% since 1966. He appears to agree with Banaszak on the urgency of the problem, saying in a press statement: “At the current levels of destruction, and given the lack of conservation action, the reefs will most likely disappear by 2050.”