Pathways to Illness from Red Tide
Red tide, or harmful algal blooms (HABs), involves the rapid growth of microscopic algae in coastal waters. These blooms, often caused by Karenia brevis, produce potent natural toxins that can affect human health.
Inhalation of airborne toxins is a primary way people become ill. As waves break, they release microscopic particles containing toxins, like brevetoxins, into the air. These aerosolized toxins can be carried by winds along coastlines, leading to respiratory exposure.
Direct skin contact with red tide water is another pathway for illness. Swimming, wading, or other water activities in bloom-affected areas can expose skin to algal toxins. While less common than inhalation, direct contact can still result in adverse reactions.
Consuming seafood with accumulated red tide toxins is a significant route to illness. Filter-feeding shellfish, such as oysters, clams, and mussels, ingest toxin-producing algae and concentrate toxins in their tissues. When eaten, these contaminated shellfish can transfer toxins to humans.
Common Symptoms of Exposure
Symptoms from red tide exposure depend on the pathway of contact. Inhaling airborne toxins commonly causes respiratory irritation, including coughing, sneezing, and a scratchy throat. Those with pre-existing respiratory conditions like asthma may experience more severe symptoms, such as wheezing and shortness of breath.
Skin contact with red tide water can cause localized irritation, such as a rash, itching, or eye irritation. These reactions are typically mild and resolve after leaving the affected water.
Ingesting contaminated seafood can lead to more severe and systemic symptoms. Shellfish poisoning may cause gastrointestinal issues like nausea, vomiting, and diarrhea, or neurological symptoms such as tingling in the lips, tongue, or extremities. More severe forms can lead to dizziness, incoordination, and temporary paralysis.
Symptoms can appear minutes to several hours after consuming contaminated seafood. Seeking medical attention is advisable if these symptoms occur after eating shellfish during a red tide event.
Staying Safe During Red Tide
Protecting oneself during a red tide event involves minimizing toxin exposure. Regularly check local advisories from health and environmental agencies for information on bloom locations and health risks.
Avoiding affected beaches and waters is a primary safety measure. If a beach is under a red tide advisory, avoid swimming, wading, or other water-based recreation to prevent skin exposure and inhalation. Always heed warning signs posted at beach access points.
Staying indoors with windows closed and air conditioning running reduces exposure to airborne toxins, especially for those with respiratory sensitivities. Using air conditioning in “recirculate” mode prevents outside air from entering the home.
Keep pets away from the shoreline and out of the water during a red tide. Animals can be susceptible to toxins if they swim in contaminated water or consume dead fish or shellfish. Rinse pets thoroughly with fresh water if they contact bloom-affected areas to prevent illness.
Consuming Seafood During Red Tide
Not all seafood poses the same risk during red tide events. Finfish, such as snapper, grouper, or mahi-mahi, are generally safe to eat. Toxins do not accumulate in their edible muscle tissue.
Crustaceans like shrimp, crabs, and lobsters are usually safe for consumption. They do not filter feed like shellfish, so toxins do not concentrate in their edible portions. However, remove the guts and internal organs of crabs and lobsters before cooking, as toxins might be present.
Filter-feeding shellfish, including oysters, clams, mussels, and scallops, are the primary concern. They actively filter large volumes of water, accumulating toxins from the algae in their tissues. Consuming contaminated shellfish, even if cooked, can lead to severe illness.
Observe shellfish harvesting bans issued by state and local authorities during red tide events. These bans prevent the harvesting and sale of contaminated shellfish, protecting public health. Always confirm that shellfish are sourced from areas unaffected by current red tide advisories.