For marine animals, however, the consequences can be more severe, not least because of the environment in which they live.
"They're basically paralyzed, and they're comatose," Virginia Edmonds, animal care manager of Florida mammals for the Lowry Park Zoo in Tampa, told the Tampa Bay Times. "They could drown in 2 inches of water."
Signs that a manatee has come into contact with the red tide include a lack of coordination and stability in the water, muscle twitches, seizures, and difficulty lifting its head to breathe.
Manatees are especially susceptible, because they congregate in the warm offshore waters where the blooms occur, and because fragments of Karenia brevis become attached to the seagrass that the animals eat, which means they are likely to be exposed for some time after the bloom dies down.
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According to NOAA, brevetoxin has been implicated in numerous previous manatee mass mortalities off Florida, including in 1963, 1982, 1996, 2002, and 2003; it was also fingered as the likely culprit in the deaths of more than 740 bottlenose dolphins along the US east coast in 1987-88.