Red Tides and Sea Turtles – Frequently Asked Questions

What is a “red tide”?

“Red tide” is a general term that is used to describe an increase or “bloom” of toxin-producing microorganisms (algae) that can cause water to have a reddish color. Red tide is one type of what is referred to as a harmful algae bloom or HAB. In the U.S., and the Gulf of Mexico in particular, “red tide” refers to blooms of Karenia brevis - which is a type of single-celled organism called a dinoflagellate. Karenia brevis produces a group of toxins called brevetoxins that are known to harm or kill many animals, including fish, birds, sea turtles, and marine mammals.

Where do red tides occur?

Red tides caused by Karenia brevis blooms mainly occur in the Gulf of Mexico but also are occasionally observed on the Atlantic coast of the southeastern U.S. Red tides initially form miles from shore and can be transported to coastal waters by wind and currents where they may persist for weeks or months. Sea turtle deaths associated with red tide have been documented in waters of Florida and Texas and occur most frequently along the southwest Florida coast.

How does red tide affect sea turtles?

The toxins produced by red tides – called brevetoxins - primarily affect the nervous system of animals.  Sea turtles become very weak, lethargic or unresponsive, or may exhibit other signs of abnormal neurologic function.  Severely affected turtles may drown and are vulnerable to predators. There is some evidence that red tide toxins also may affect other organ systems and the immune system in ways that we do not fully understand.

How are sea turtles exposed to red tide toxins?

Sea turtles are primarily exposed to red tide toxins through their diets. Toxin levels can be high in sea turtle food such as marine invertebrates and seagrasses. Also, sea turtles may feed on fish that die from red tides, which often contain high levels of toxins.

What can be done to help sea turtles during a red tide?

Some sea turtles affected by red tides are found alive and are cared for by permitted sea turtle rehabilitation facilities.  Treatment is mainly supportive care and administration of medications that help turtles clear the toxins from their bodies.  Some turtles recover relatively quickly, others require more prolonged care. 

Red tides eventually become less potent and eventually disappear.  There is nothing humans can do to hasten this process.

Are red tides caused by human activity?

Human activity does not cause red tides, but it may worsen them. Red tides are natural phenomena that have been documented in the Gulf of Mexico for hundreds of years, well before dense human settlement. However, once a red tide forms and moves into nearshore waters, nutrients from coastal pollution may prolong and intensify it.

What do I do if I see a stranded sea turtle?

If you see a sick, injured, stranded, or dead marine mammal or sea turtle, immediately contact your local stranding network.