Red Tide

In Florida, red tide is caused by a naturally-occuring marine plankton (microscopic algae) called Karenia brevis, abbreviated K. brevis. It is found most commonly in the Gulf of Mexico. K. brevis produces several types of neurotoxins, the most impactful of which are brevetoxins. Whether they are ingested or inhaled, brevetoxins can be extremely harmful to manatees and cause seizures that lead to drowning.

Since the recording of manatee deaths from red tide began in 1982, there have been extensive die-offs (more than 50 manatees) in 1996, 2003, 2005, 2006, 2007, 2013, 2016, 2017, 2018, and 2021.

If a manatee exposed to red tide can be moved out of the affected area by trained biologists and stabilized at a critical care facility, it is likely to recover. There are many manatees that would not be alive today if a boater or paddler had not called to report them.

You can do your part to help manatees suffering from red tide exposure by knowing the signs:

  • facial twitching
  • lethargy
  • swimming sideways in the water
  • inability to surface to breathe

If you see a manatee suffering from any of the above, please report it immediately to the Florida Fish and Wildlife Conservation Commission by calling 1-888-404-3922.

Two rescuers use a floatation device hold a manatee's head above water to help them breathe.

A flotation device is positioned under a manatee suffering from red tide, so the manatee can breathe. Red tide acts as a neurotoxin in manatees, giving them seizures that can result in drowning. Photo courtesy Tim Martell.

Despite its name, a red tide bloom may discolor the water red, green, or brown. While red tide “blooms”—in which the organism occurs at high concentrations—are not uncommon, they can be classified as a type of harmful algal bloom (HAB) due to their negative impact on the environment, marine life, and humans. In high concentrations, brevetoxins can harm or kill fish, birds, and marine mammals by impacting their central nervous systems. They can also negatively affect humans in our coastal communities by irritating the eyes, nose, and throat.

Manatees can be harmed by ingesting and/or inhaling (breathing in) the brevetoxins produced by red tide organisms. In the case of ingestion, it might take several weeks of eating seagrass or taking in seawater contaminated by brevetoxins. Wave action can also easily break open K. brevis cells and release their toxins into the air, where they are then inhaled by manatees when they surface to breathe. In both instances, the brevetoxins can cause seizures and lead to drowning.

As is the case with other types of HABs, large blooms of red tide can reduce the amount of light penetration in the water and prevent the growth of seagrass, which is a primary food source for manatees. Although red tide is a natural phenomenon, its frequency, duration, and severity are worsened by large inputs of nitrogen and phosphorus into the ocean from man-made sources such as fertilizer and waste water.

To find out the current status of red tide in Florida, please see the Florida Fish and Wildlife Conservation Commission’s web page Red Tide Current Status and statewide map of the past eight days of red tide sampling. (links are external)