That seafood dinner in Martinique twenty years ago still haunts Caroline Montout-Joseph, a social worker who suffered months of agony after eating a mahi-mahi at a beachside restaurant in the resort town of Les Trois-Îlets. She was diagnosed with ciguatera, a form of fish poisoning.
“At first, I could handle it, but as the day went on, the pain grew worse and worse until it got horrible,” said the 53-year-old mother of two. “In terms of intensity, it was as bad as childbirth contractions.”
Ciguatera is caused by toxins produced by microscopic algae in the genus Gambierdiscus, which thrive on seaweed that colonizes dead or dying coral. When reef fish consume these algae and are in turn eaten by humans, the toxins can cause severe illness.
“Ciguatera is widespread all over the planet, specifically in tropical regions,” said Dr. Philipp Hess, who heads a unit that studies toxic microalgae at a France’s marine research agency.
The World Health Organization estimates 50,000 to 500,000 cases of ciguatera globally each year. A growing body of research suggests the actual number could be much higher due to underreporting.
Yet data remains sparse —especially in the Caribbean, where few islands operate comprehensive surveillance programs or publish case counts.
Now, scientists are warning that the problem may worsen in many areas as coral reef die-offs, driven by warming seas and other climate pressures, fuel the spread of toxic microalgae. Still, experts caution that while climate change is fueling conditions favorable to toxic microalgae, there is not yet conclusive evidence that these organisms are more widespread than in the past.
While rising temperatures may simultaneously reduce risk in other places, experts say more education, research and monitoring are urgently needed to protect Caribbean residents and the more than 40 million tourists who visit the region each year.
Photo by Freeman Rogers | The BVI Beacon
175 symptoms, but no cure
Though rarely fatal, ciguatera has been linked to more than 175 gastrointestinal, cardiovascular and neurological symptoms, according to the WHO. There is no cure, but doctors use various treatments to ease patients’ suffering.
In Martinique, Montout-Joseph was taken to the emergency room, where she was given pain medication through an IV, but she experienced bloating, spasms and nausea for a few days. The symptoms faded after that, but they returned every couple of months for more than a year.
“The pain would come back with vomiting, and it was intense,” she said during an interview in downtown Fort-de-France, the island’s capital. “It would last 24 hours and then go away.”
Photo provided
About a decade later, her husband Philippe, a musician, also got poisoned in Martinique.
“It was a mahi-mahi that his cousin had just caught,” Montout-Joseph said.
Her husband’s symptoms were different from hers.
“He started vomiting and having intestinal problems,” she said, adding that severe muscle spasms caused him to “bend over like a mummy.” Eventually, he fell and injured his forehead.
Though his symptoms were “extremely violent,” she said, they only lasted 24 hours, and he then made a full recovery.
Other ciguatera symptoms include tingling, numbness, vertigo, depression, anxiety and a neurological effect that reverses the sensations of hot and cold. In one in five cases, symptoms persist for three months or more, according to a report by the WHO and the Food and Agriculture Organization of the United Nations.
Long history
Ciguatera, however, is not a new phenomenon. The first reports of poisonings known to Europeans were recorded in the 1500s in the West Indies, according to United States Virgin Islands marine biologist and ciguatera researcher Dr. Tyler B. Smith.
But for centuries after that, the root cause of the condition was unknown, Smith said during a public talk in January.
“The name comes from Cuba, where they thought it was a problem that occurred with these turbo snails, which they called locally ‘cigua.’ And that’s how we got the name ciguatera,” said Smith, who contributes to a U.S. federal grant-funded project called the Greater Caribbean Center for Ciguatera Research (GCCCR).
Today, the real cause of the food poisoning is common knowledge among scientists: It is caused by toxic microalgae of the Gambierdiscus genus, named after the Gambier Islands of French Polynesia. These single-celled organisms typically enter the food chain when small reef fish or other creatures eat the seaweed they colonize.
In the Caribbean
Smith and other scientists with the five-year GCCCR initiative are working to learn more about the prevalence of ciguatera in the Caribbean.
GCCCR partner Dr. Alison Robertson said their research shows ciguatera is widespread across much of the region, contradicting a popular belief, supported by earlier findings and anecdotal evidence, that it is largely limited to a few hotspots.
“We’ve certainly seen prevalence of ciguatera throughout the lower Antilles Islands as well and into Central America, South America,” said Robertson, an associate professor at the University of South Alabama.
Her GCCCR colleague Dr. Michael Parsons, a professor of marine science at Florida Gulf Coast University, estimated that “5 to 10% of seafood consumers across the islands” may be at risk of being infected during their lifetime.
But accurate data is elusive: “Only about one-tenth to one-fourth of cases are typically reported,” Parsons said.
Because the toxic algae thrive on seaweeds in calm waters, Robertson said certain areas of individual islands face a higher risk.
“They don’t like high wave action; they don’t like a lot of turbulence,” she said, adding that the species “tend to do well in areas that are on the leeward side of islands.”
Puerto Rico and the U.S. Virgin Islands, which mandate case reporting, are among the Caribbean islands most adept at tracking the poisoning, Robertson said.
But even there, she said, the official data are far from showing the full picture.
“We might have fishermen that have had ciguatera twenty times, but they’ve been to the doctor once in their lifetime,” she said, adding, “The estimates are always going to be fuzzy at best.”
Photo by Freeman Rogers | The BVI Beacon
Data dearth
A 2015 study in Florida found ciguatera rates up to 28 times higher than public records showed —nearly 1 per 1,000 people per year in the county that includes the Florida Keys.
A 2013 study by Smith reported a far higher rate in the U.S. Virgin Islands: about 12 per 1,000 people annually.
“That’s actually a really high rate of incidence of any disease in a human population,” Smith said during his January presentation.
The worst-affected areas were the south sides of St. Thomas and St. John, which he called “hyperendemic” for ciguatera poisoning, meaning the disease is constantly present in the population and occurs at unusually high levels.
The northern sides of those islands —like the southernmost island of St. Croix— are not impacted as much, he added.
In 2024, a total of 27 cases of ciguatera poisoning were reported in Puerto Rico, according to the Department of Health.
Getting worse?
As climate change devastates coral reefs and reshapes ecosystems across the Caribbean, many scientists fear that ciguatera poisoning could become more widespread.
“The scientific literature clearly shows an ecological link between reef degradation and an increase in Gambierdiscus abundance,” said Lise Cameroun, head of the Food Safety Unit in Guadeloupe.
Dr. Philipp Hess explained the mechanism: When corals die, seaweed quickly takes over, creating an ideal habitat for toxic microalgae. As a result, he said, many scientists believe that rising coral mortality will drive up the prevalence of ciguatera toxins.
This potential link remains unconfirmed, he added, but, “the trend is there.”
Still, the science is not settled. Other researchers have found that environmental conditions affecting the algae are more complex than once believed.
Dr. Alison Robertson, for example, pointed out that the toxic microalgae “don’t like it too hot,” suggesting that extreme ocean warming might limit their growth in some areas.
Dr. Michael Parsons predicted a possible shift in their distribution: the algae could migrate to “deeper, cooler waters” and expand “into the Gulf of Mexico and up the east coast of the United States.”
However, he noted, their need for sunlight could restrict their ability to thrive in deeper zones. It also remains unclear how rising temperatures will affect the toxins themselves.
“Fishing pressure and overfishing can greatly influence grazing, predation, and the vectors moving the toxins into fish,” he added. In some areas, fishing removes grazing fish that would normally be eaten by predators like barracudas. With fewer of those prey available, barracudas may feed on species that carry less toxin, reducing how much ciguatera they accumulate. In this way, fishing can disrupt the food chain and alter the movement of toxins through marine ecosystems.
Residents’ burden
With few comprehensive government programs in place, the burden of managing ciguatera often falls to individual Caribbean residents.
In the British Virgin Islands (BVI), officials issue occasional outbreak warnings but don’t regularly publish data about the illness.
“To understand ciguatera, you have to understand what causes it: a stagnant body of water that builds up algae,” said BVI fisherman Zacchari Stoutt.
In the BVI, he added, fishers know to avoid certain fish on the south side of the most populous island of Tortola. Unlike the island’s north side, which is exposed to the open ocean, much of the south side is protected and water circulation is limited, he explained.
Additionally, marine traffic is heavier on the south, where several marinas and docks are located.
“Those marinas, when they get dirty, they stay dirty, and it takes a couple months before they get clean,” he said. “So very stagnant water.” BVI fishers, he added, know that such conditions elevate the risk for possible ciguatera contamination in reef fish.
“I would eat any barracuda on the north side,” he said. “I would not eat barracuda on the south side, because they feed off of the fish that contains the ciguatera.”
In Haiti, where data is also lacking, marine conservationist Jean Weiner recounted a friend’s near-fatal case of ciguatera. “I do not eat fish in Haiti unless I’m in more remote areas,” he said. “If I’m in, for example, Cap-Haitien or Port-au-Prince or bigger urban areas, I will not eat fish.”
In Jamaica, the U.S. Centers for Disease Control warned in April that outbreaks are “sporadic and underreported,” citing a 2020 episode linked to barracuda.
In the Bahamas, Dr. Arlington Lightbourne, the president of Bahamas Wellness Health Systems, sounded the alarm in August 2021.
“Please stop eating barracuda!” the doctor told Eyewitness News.
The species, he said, is the most common source of ciguatera in the Bahamas region.
“I would guess that every physician in The Bahamas has treated at least one [case],” he said. “Leave the large fish like barracuda or any normally mid-size fish like grouper, that is extraordinarily large, alone. The longer the fish has been in the sea, the greater the chances are that it has some form of toxicity.”
Guadeloupe’s Crackdown on Toxic Fish
The French overseas departmentof Guadeloupe stands out in the region for its vigorous efforts to combat ciguatera.
Since 2002, authorities there have restricted the sale of fifteen types of reef fish deemed “hazardous.”
The sale of four species is strictly prohibited: barracudas, yellow jacks, and two species of amberjack. Selling another nine species, including the moray eel, is banned if the specimens were caught north of the 16°30 latitude line (halfway between the 16th and 17th parallels).
And two other species —including blackfin snappers— are banned only for animals weighing more than one kilogram (2.2 pounds), regardless of where they were caught.
Image provided
These regulations are summarized in a colorful poster displayed widely across the island.
“We’re trying to encourage all fishmongers, all fish vendors, all fish markets, to display this poster for all to see, so that consumers can be informed,” Cameroun said.
Enforcement is strict. In March 2025, two fishermen were arrested on suspicion of illegally importing fish from Saint Barthélemy, another French overseas territory located about 120 miles northwest of mainland Guadeloupe —and well beyond the 16°30 latitude line. The arrests sparked controversy among fishing unions and raised concerns that the fish may have carried ciguatera.
Such strict regulations could explain a drop in the number of known cases of ciguatera poisoning in Guadeloupe over the past decade, from about 30 in 2012 to a dozen cases per year in 2023 and 2024, according to Cameroun.
Still, officials are updating the banned species list in cooperation with food safety researchers.
“We noticed that we had quite a few cases of poisoning that weren’t linked to the species on the list, but to other species,” she said.
A new policy could be in place by year’s end.
Building capacity
Other Caribbean islands are making progress in managing ciguatera, often despite limited funding. St. Kitts and Nevis sent a scientist for toxin-identification training at the University of South Alabama in May 2024.
“They then brought St. Lucia into the picture as well, and we started working with folks in St. Lucia,” Robertson said, noting that both countries “have a strong desire and a really good capacity” to improve monitoring. “The goal is to have a little bit more training and work there so that we can help them.”
Still, challenges remain. The five-year GCCCR project is set to end in August 2026, and research is difficult due to the complex biology of the toxic algae.
Despite its small size, Hess said, the organism’s genetic makeup “can be up to 100 times larger than the human genome.”
“There’s still a lot to discover about the biology of these unicellular algae and the whole issue of Gambierdiscus and toxin carriers —and the whole chain right up to human poisoning,” he added. “There are still many, many things to discover, in fact.”
This investigation, the third installment in the special series Corals: The Caribbean’s Silent Collapse, is the result of a fellowship awarded by the Centro de Periodismo Investigativo’s Journalism Training Institute and was made possible in part with the support of Open Society Foundations.
