Barracuda: Photo by Florida Keys National Marine Sanctuary

“It’s important to know that if you eat one of these large, carnivorous fish from tropical or subtropical areas, including South Florida, there is a risk. And if you get sick after eating them, you should see a doctor and let them know you’ve eaten saltwater fish,” epidemiologist Elizabeth Radke from Emerging Pathogens Institute at the University of Florida

Rising global ocean temperatures, due to climate change, will cause an increase in ciguatera seafood poisoning in the Gulf of Mexico and the SE Atlantic NOAA reported in a study published by the journal Ecological Modeling.

People can be affected by ciguatera , the most common form of algal-induced seafood poisoning, by eating contaminated tropical marine reef fish such as grouper, snapper and barracuda. The fish can become contaminated with ciguatoxins, potent neurotoxins produced by Gambierdiscus, a microscopic algae common in the tropics. Ciguatera-causing algae are abundant in the Caribbean, and ocean warming would enable some of those species to move northward, increasing its presence in the Gulf of Mexico and U.S. southeast Atlantic. Warmer temperatures could also mean larger and longer blooms of harmful algae, including those that produce ciguatoxins. In the Caribbean, Gambierdiscus are already near the top of their preferred temperature range. Higher temperatures are likely to inhibit the growth of these cells, slightly decreasing the risk of ciguatera in the Caribbean.

The toxin can travel through the food chain– from dinoflagellates or marine plankton to humans. "The toxin is transferred through the food web as the algae is consumed by herbivorous fish, which are consumed by carnivorous fish, which are in turn consumed by humans.” As it turns out, big carnivorous fish can eat dinoflagellates and ingest it, as the researchers explained, “It gets concentrated as it moves up. That’s why eating the big fish is the most dangerous.” PubMed noted that the thermal optimum for five of six Gambierdiscus species tested was 29 C or 84.2 F. This is why the algae will move northward, it will seek cooler waters as the Caribbean continues to heat.

Research titled Effects of ocean warming on growth and distribution of dinoflagellates associated with ciguatera fish poisoning in the Caribbean can be seen here.

The growth and abundance of Gambierdiscus and Fukuyoa species in the Gulf of Mexico are expected to change in response to higher temperatures, although the response of individual species depends on the location. In the more temperate portions of the northern Gulf and the U.S. southeast Atlantic coast, the abundance of all Gambierdiscus and Fukuyoa species is projected to increase with higher average growth rates. Species such as G. carolinianus and Gambierdiscus ribotype 2, which are tolerant of lower water temperatures, are expected to undergo range expansions northward as the ocean warms. Where water temperatures are higher in the eastern Gulf of Mexico and Caribbean Sea, warm-tolerant species like G. belizeanus, G. caribaeus and F. ruetzleri will become increasingly dominant. This prediction does not necessarily mean species with lower thermal tolerances will be unable to survive in the Caribbean Sea, but that these species will be less prevalent.

The World Health Organization highlighted the work of Lora E. Fleming of the NIEHS Marine and Freshwater Biomedical Sciences center. From her Clinical Presentation we can see how the consumption of contaminated seafood affects the human body. It does not sound pleasant.

Ciguatera presents primarily as an acute neurologic disease manifested by a constellation of gastrointestinal (diarrhea, abdominal cramps and vomiting), neurologic (paresthesias, pain in the teeth, pain on urination, blurred vision, temperature reversal) and cardiovascular (arrhythmias, heart block) signs and symptoms within a few hours of contaminated fish ingestion. The pathneumonic symptom of Ciguatera intoxication is hot/cold temperature reversal, although not all patients report this. The attack rate has been reported to be 73%-100% with ingestion of contaminated fish, without any apparent age-related susceptibility. Acute fatality, usually due to respiratory failure, circulatory collapse or arrhythmias, ranges from 0.1% to 12% of reported cases; presently in the Pacific, the mortality is less than 1%. Lethality is usually seen with ingestion of the most toxic parts of fish (ie. the liver, viscera, roe and other organs). The clinical picture may be variable among individuals, even with the same food source, different ethnic groups, and possibly with different types of fish and/or geographic location. It appears that ciguatera from consumption of carnivore species may be more toxic than that from consumption of herbivores due to exposure to more than one toxin and/or transformation of the toxin(s) and/or an increased dose response. In Polynesia, Ciguatera is dominated and initiated by neurologic symptoms (90% of patients report paresthesias and dysesthesia), while reports from the Caribbean suggest that Ciguatera initially presents acutely as a gastroenteritis often with associated cardiovascular symptoms, with the gradual onset and dominance of neurologic symptoms over the first 24 hours. This may be due to different toxins mixtures elaborated by Caribbean and Polynesian G. toxicus. The symptoms of Ciguatera poisoning, especially the paresthesias and weakness, can persist in varying severity for weeks to months after the acute illness. Prolonged itching due to chronic Ciguatera can present as a dermatologic disease when it is really due to ciguatera paresthesias. Chronic ciguatera can also present as a psychiatric disorder of general malaise, depression, headaches, muscular aches, and peculiar feelings in extremities for several weeks. It is reported that those with chronic symptoms seem to have recurrences of their symptoms with the ingestion of fish (regardless of type), ethanol, caffeine, and nuts 3 to 6 months from initial ingestion. Ciguatera can be sexually transmitted. With exposure of the mother, premature labor and spontaneous abortion have been reported, as well as effects on the fetus and newborn child through placental and breast milk transmission.