Red Tide harms Manatees and they are severely affected by red tide, which can be fatal. The red tide organism common in the Gulf of Mexico, Karenia brevis, produces potent neurotoxins called brevetoxins that damage the manatees’ central nervous systems and can lead to seizures and drowning.
How Manatees are Exposed to Red Tide
Manatees can be exposed to brevetoxins in two primary ways:
- Ingestion: Red Tide Harms Manatees! They consume the toxins when they eat contaminated seagrass, which accumulates the brevetoxins during a bloom. The toxins can remain in the seagrass for weeks after a red tide has dissipated.
- Inhalation: When waves break, they can rupture the K. brevis cells and release the toxins into the air as an aerosol. Manatees inhale these airborne toxins when they surface to breathe.
Symptoms of Brevetoxicosis
Signs that a manatee is suffering from red tide poisoning (brevetoxicosis) include:
- Lethargy or weakness
- Facial twitching or tremors
- Abnormal swimming (e.g., swimming sideways or in circles)
- Inability to surface to breathe, which can lead to drowning
- Beaching in shallow water
- Seizures or paralysis
Red Tide Harms Manatees – Impact and Mitigation
Red tide has caused extensive die-offs, with mass mortality events recorded in Florida in numerous years, including 1996, 2013, 2018, and 2021. In 2018, red tide was responsible for 288 manatee deaths.
If a manatee is found alive but in distress due to red tide exposure, trained biologists can move it to a critical care facility for stabilization and rehabilitation. Many manatees have recovered and been released back into the wild thanks to these rescue efforts.
How You Can Help Florida Manatees
If you see a sick, injured, or dead manatee, you should immediately report it to the Florida Fish and Wildlife Conservation Commission (FWC) Wildlife Alert Hotline at 1-888-404-3922.
What toxins cause red tide and how do they harm manatees?
The toxins that cause red tide in Florida and harm manatees are called brevetoxins. These potent neurotoxins are produced by the microscopic algae species Karenia brevis, the organism responsible for the blooms.
How Brevetoxins Harm Manatees
Brevetoxins primarily affect the central nervous system by binding to voltage-gated sodium channels in nerve cell membranes, which causes the channels to open and leads to uncontrolled nerve firing and cell depolarization. This disruption of normal nerve function leads to severe physiological effects and can ultimately be fatal for manatees.
Manatees are exposed to these toxins through two main pathways:
Ingestion
Manatees are herbivores that primarily feed on seagrass. During a red tide event, brevetoxins accumulate in the seagrass and on the epiphytes (small organisms and algae) growing on the blades. When manatees consume this contaminated vegetation, they ingest high concentrations of the toxins. Mass mortality events are often linked to this dietary exposure, as the toxins can remain in the seagrass for weeks, even after the red tide bloom has dissipated from the water column.
Inhalation
K. brevis cells are fragile and are easily broken apart by wave action. This process releases the brevetoxins into the air as an aerosol. Manatees, as air-breathing mammals, inhale these airborne toxins when they surface to breathe. The toxins can damage their lungs and respiratory tract, leading to significant respiratory distress.
Resulting Symptoms and Death
Once the toxins are in the manatee’s system, they cause:
- Neurological impairment: Symptoms include muscle twitches, tremors, lack of coordination (ataxia), and partial paralysis.
- Loss of equilibrium: Affected manatees may exhibit abnormal swimming behavior, such as swimming in circles or on their side.
- Respiratory failure/Drowning: The toxins can paralyze the manatee’s muscles, including those necessary for breathing and swimming to the surface, causing them to drown.
- Immune suppression: Sublethal exposure has been shown to affect the manatee’s immune system, making them more susceptible to other health issues.
These severe impacts make red tide one of the most significant natural threats to the Florida manatee population, with major die-offs documented regularly over the past several decades.