For more than 20 years, Mexican biologist Dr. María del Carmen García Rivas has led a crusade to protect the coral lining the Yucatan Peninsula in the Caribbean Sea.
As director of the Puerto Morelos Reefs National Park in México, she has advocated for reforms to reduce runoff and other pollution from coastal development. She has spearheaded efforts to control lionfish, an exotic invasive species that has put at risk the nearly 670 species of marine fauna that inhabit the park.
And since 2018, she has organised brigades to restore reefs damaged by tissue-destroying coral diseases known as white syndromes.
But now, yet another threat has been keeping her awake at night: massive blooms of sargassum seaweed reaching the coast of the park.
“When the sargassum, a macroalgae that usually floats, reaches the coasts, it begins to decompose, generating an environment without oxygen that kills different organisms,” she said. “It mainly affects species that cannot move or move very little, such as some starfish, sea urchins, the sea grasses themselves, and of course corals.”
People pick up excess sargassum from the Mexican coast in the Mayan Peninsula. (Photo: GLADYS SERRANO EL PAÍS )
Along the coast of Quintana Roo, the Mexican state where the Puerto Morelos Reefs National Park is based, the local government collected 70 tons of sargassum during 2023 alone, said Huguette Hernández Gómez, the state’s secretary of ecology and environment. Added to what they collected during the last four years, the figure reaches 200 tons.
Regional problem
This story is familiar across the Caribbean region. Though modest amounts of sargassum benefit marine life in the region, massive influxes arriving since 2011 have upset the ecological balance in some areas in ways that could be irreversible. The seaweed, for instance, has exacerbated existing stress on the region’s reefs, which last year faced a massive bleaching event linked also to warming waters associated with climate change.
Exposure to extreme temperatures for extended periods breaks down the relationship between the corals and the algae living inside of them. Corals are left pale or white, and the lack of food from algae can lead them to die, according to the United States National Oceanic and Atmospheric Administration (NOAA).
Sargassum mats have also blocked sea turtle nesting sites and inundated mangroves, which serve as crucial nurseries for countless aquatic species.
In some areas, beaches have been eroded by the seaweed and by the heavy machinery used to remove it. Many fishers complain that their catch has dwindled sharply.
But because of the magnitude of the relatively recent problem — which is affecting coastlines from West Africa to the Americas — the true extent of the environmental damage is poorly understood, according to Dr. Brian Lapointe, a biologist and sargassum expert at Florida Atlantic University.
“We haven’t gotten very far in the research to understand the causes or how to deal with it and manage and mitigate the impacts on the environment,” Dr. Lapointe said.
Second largest barrier reef
The effects that Dr. García Rivas has seen in Mexico illustrate the implications for the entire region. The park she oversees is part of the Mesoamerican Barrier Reef System, which stretches along more than 600 miles of coastline in Mexico, Belize, Guatemala and Honduras.
As the second longest barrier reef in the world — only the Great Barrier Reef in Australia is longer, at about 1,400 miles — the Mesoamerican Barrier Reef is home to some 500 species of fish and 60 species of stony corals, according to the World Wildlife Fund (WWF). It also supports the livelihoods of one to two million people in the region, the WWF states.
Sargassum surrounds a dock along the Mexican coast of the Mayan Peninsula. (Photo: GLADYS SERRANO
