MIAMI, March 11 (Reuters) - A red tide algae bloom has killed a record 174 manatees so far this year off Florida's southwest Gulf Coast, authorities said on Monday.
The Florida Fish and Wildlife Conservation Commission said it was the highest number of red-tide-related manatee deaths in any single calendar year.
The previous record was set in 1996 when red tide killed at least 149 manatees, mostly in March and April.
The Florida manatee, averaging 10 feet (3 metres) long and 1,000 pounds (454 kg), has long hovered on the edge of extinction and it is covered under the U.S. Endangered Species Act of 1973.
Florida officials said 81 of the herbivorous marine mammals died last year and that 205 had died of all causes so far in 2013.
The one-cell organism that causes red tide releases a toxin when it dies, sickening manatees.
"Signs that a manatee is affected by red tide include a lack of coordination and stability in the water, muscle twitches or seizures and difficulty lifting its head to breathe," the Fish and Wildlife Conservation Commission said in a statement.
It said the current red tide off Florida's southwest coast had first been detected in September. (Reporting by Tom Brown; Editing by Cynthia Osterman)