Some 'Red Tides' are linked to shellfish poisoning.  Red tides are caused by the explosive population growth of a minute, single-celled group of algae called dinoflagellates. Red tides may be stimulated by excessive runoff of nutrients from land or by the discharge of untreated sewage into coastal waters, both of which serve as fertilizers for the algae. Some red tide organisms produce toxins that are concentrated by filter-feeding animals such as clams, mussels, oysters, and crustaceans and can cause illness or death in animals or humans eating the contaminated animals.

  What is Paralytic Shellfish Poisoning or PSP?

PSP, also known as Red Tide, is the contamination of bivalve shellfish by micro-organisms called dinoflagellates. When people eat shellfish contaminated with these micro-organisms, death may result.

How do the shellfish get contaminated?

These micro-organisms are always in the water. When conditions such as salinity, temperature, and nutrients are right, the micro-organisms have a population explosion known as blooms. Little is known on how or why the organisms produce the toxin, but as the hinged shellfish filter feed on the blooms they store vast amounts of the toxin in their tissue, without being affected.

What is the toxin?

The toxin produced is among the most potent natural poisons in the world. There is no known antidote.

Why is it called 'Red Tide'?

Red Tide does not always mean the water will appear red. The organism can have many different pigments, resulting in different colours in the water or no colour change at all.

What shellfish families are affected?

Please look at our Red Tide Poster to see some of the shellfish affected.

What are the signs and symptoms of PSP?

Common symptoms are tingling or numbness beginning around the lips and spreading to the face and neck within one half hour of ingestion. This is followed by headache, dizziness, nausea, and a feeling of weakness. Similar sensations happen in the fingertips and tongue, followed by loss of voluntary movement. Rapid pulse and difficulty in breathing can occur. Cardiac failure and paralysis of the chest and diaphragm can cause death within 12 hours.

What do I do if PSP is suspected?

If PSP is suspected, seek medical attention IMMEDIATELY. Induce vomiting and do not give any alcohol.

Be sure to check out our Red Tide Poster for more information and pictures!

• Harmful algae page at Wood's Hole Oceanographic Institution
• Solutions to Avoid Red Tide
• Red Tide in Texas - FAQ

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