Red tide and food poisoning: what you need to know

What is the red tide?

A “red tide” is a type of harmful algal bloom, or HAB. It happens when algae grows so much in an area of ​​the ocean that it discolors the water, often with a reddish or reddish-brown color. These red tides can produce toxic substances for fish, marine animals, birds and humans. They usually occur in late summer and early fall.

Not all algae blooms are bad. Sometimes they are part of the natural cycle of the ocean and simply provide a food source for certain types of marine life.

What causes red tide?

Types of algae known to produce red tide include Karenia brevis, Alexandrium catenellaand Alexandrium fundyense. A red tide occurs when one of them gets out of control.

Scientists still don’t know the exact combination of factors that cause this uncontrolled growth. In general, higher temperatures and more rain combined with less wind than normal alter seawater. They make it warmer, saltier, and allow more nutrients to accumulate. Runoff water containing agricultural pesticides or fertilizers may also flow into this water. All of this leads to massive algae growth.

Scientists continue to investigate ways in which humans might control these blooms.

How is a red tide harmful?

When algae reach these levels, they consume oxygen in the water, killing many animals that live there. The bodies of these animals contaminate the waters and shores in the red tide area.

Red tide algae also make toxins, although scientists aren’t sure why. These toxins can damage the respiratory and digestive systems of wildlife and local people.

They can also accumulate in certain “grazer” fish, such as krill, and in crustaceans. It can sicken large fish, mammals and humans if they feed on it.

Fish and other seafood that have high levels of these toxins look or taste no different from those that are not contaminated. Cooking or freezing fish does not kill toxins.

What are the symptoms of red tide poisoning?

Especially in warmer climates, red tide toxins in the air and water can cause problems with allergic reactions, minor respiratory problems, and irritation to the skin and other areas.

In colder regions, food poisoning from eating shellfish containing algae toxins is more likely. This can lead to :

  • Paralytic Shellfish Poisoning (PSP): You get this from shellfish eating PSP toxins made by the red tide alexandrium species of algae. It can change how your nerves work and even paralyze you. This happens in the United States on the west and east coasts. It can be quite serious. It sometimes causes death.
  • Diarrheal shellfish poisoning (DSP): It comes from dinophysis algae. It’s more common in Europe and Japan, but it also happens in the United States. You might notice diarrhea, nausea, cramps, vomiting, and stomach pain.
  • Amnesic Shellfish Poisoning (ASP): You get it from certain types of mussels and clams, usually along the east coast of Canada. You might have an upset stomach as well as dizziness, brain fog, and memory loss.

What can you do to protect yourself against the effects of red tide?

  • Get your seafood only from reputable sources. Online resources such as the Monterey Bay Aquarium’s Seafoodwatch.org can help you make healthy, safe and sustainable choices.
  • Don’t eat shellfish like oysters and clams that come from a red tide area. Consult your doctor if you think you have eaten contaminated shellfish or if you feel sick after eating shellfish.
  • Stay away from known red tide areas. This will help prevent eye, nose and throat irritation that can occur when swimming in water or breathing air. And don’t swim if you notice discolored water or dead fish on the shore.

How to Treat Symptoms of Red Tide Poisoning

Symptoms of illness resulting from exposure to red tide usually do not last long. They usually disappear when you leave the red tide area. Still, it’s best to avoid contact with these algae blooms, especially if you have respiratory problems like asthma.

Over-the-counter allergy medications (antihistamines) can help relieve minor respiratory issues and skin irritations related to red tide. Over-the-counter medications can help with tummy issues. Be sure to drink plenty of fluids so you don’t become dehydrated.

If you suspect you have become ill from eating seafood contaminated with red tide toxins, notify your local health department and let them know where authorities can follow up and issue a warning for that area if necessary.

How can I find out about current red tides?

The National Centers for Coastal Ocean Sciences maintains a webpage that provides harmful algal bloom forecasts by region of the United States. You can also check local municipality websites like Florida, Texas, California, and other areas with regular red tides.

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