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Algae—far more than the green film on a fish tank—forms the base of marine food webs, supplying nutrients to countless organisms. When certain species produce toxins and bloom uncontrollably, they threaten human health. One of the most concerning of these toxins is domoic acid, linked to memory loss.

First identified in 1991 off the U.S. West Coast, domoic acid is produced by only 28 known diatom species. Recent research published in Diatom Research detected the toxin in farmed shellfish on Luzon Island, Philippines, during a May 2023 bloom. The compound accumulates in shellfish tissues and survives freezing or cooking. Consuming large amounts can trigger amnesic shellfish poisoning (ASP), characterized by short‑term memory loss, abdominal cramps, diarrhea, nausea, and vomiting within the first 24 hours. Severe cases may involve confusion, dizziness, and respiratory secretions.

While ASP incidents remain rare, the frequency of harmful algal blooms is climbing—driven largely by human activity—raising the likelihood that domoic acid reaches consumers. Fortunately, fisheries and wildlife agencies routinely test seafood to curb this risk.

Other Algal Toxins and Their Health Impacts

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Algae produce a spectrum of toxins, each associated with distinct food‑borne illnesses:

• Saxitoxin causes paralytic shellfish poisoning. Symptoms appear within hours and include gastrointestinal upset, tingling or numbness in the limbs, mental changes, rapid heart rate, hypertension, and in severe cases, respiratory paralysis or asphyxiation.
• Brevetoxin leads to neurotoxic shellfish poisoning. Patients experience dizziness, muscle weakness, nausea, tingling in the limbs and mouth, slurred speech, and respiratory discomfort.
• Okadaic acid produces diarrhetic shellfish poisoning. While most sufferers report only gastrointestinal symptoms—abdominal pain, diarrhea, nausea, vomiting—some may also develop chills, fever, and headache.
• Ciguatoxin is the culprit behind ciguatera. This illness presents a broad range of gastrointestinal and neurological signs, plus cardiac effects such as arrhythmias, hypertension, and bradycardia.