MELBOURNE, Fla. (USA Today) - Toxic, oxygen-depleting algae blooms are killing manatees at a record-breaking pace this year in Florida, biologists say.
Through Tuesday, 769 endangered sea cows have died so far this year across the Sunshine State, the Save the Manatee Club reported. That constitutes Florida's largest annual manatee die-off since record-keeping began, with two more months left to go.
The previous record of 766 documented dead manatees was set in 2010. That's when hundreds succumbed to cold stress during an unusually chilly winter and spring, Florida Fish and Wildlife Conservation Commission biologists determined.
"Here we are, just a few years later. And now we've broken that record, which we thought probably would never be broken," said Patrick Rose, Save the Manatee Club executive director.
"With two really bad years, we're quite concerned about where we are with the population, and what needs to be done to protect it going forward," Rose said.
The Fish and Wildlife commission's annual aerial winter survey counted a record 5,077 manatees in 2010. That was before the cold-related deaths started, Rose said.
For comparison's sake, this year's toll so far is nearly double last year's total of 392 confirmed manatee deaths, FWC reported. In 2011, 453 Florida manatee deaths were reported.
Two "unusual mortality events" are prime contributors to this year's unprecedented losses, said Katie Tripp, Save the Manatee Club's director of science and conservation.
One is a toxic red-tide bloom that killed 276 manatees this winter and spring in southwest Florida. The poisonous bloom was centered in the Fort Myers-Cape Coral region.
The other event is the still-unexplained Indian River Lagoon die-off that has claimed more than 100 manatees in Brevard County. In total, Rose said more than 220 manatees have died of various causes this year in Brevard, but these mysterious 100-plus deaths appear to be triggered by "an acute intestinal event" caused by feeding changes, bacteria or virus.
One precursor was a massive 2011 algae "superbloom" that killed 47,000 acres of lagoon seagrass - the manatees' primary food source. Consecutive cold winters and extended drought, coupled with a decades-long buildup of nitrogen and other contaminants, may have shocked the ecosystem into one dominated by algae, rather than seagrass.
In a troubling statewide trend, 123 of this year's manatee victims were stillborn, newborn or young calves less than 5 feet long, the manatee conservation group reported. At least 49 of these deaths occurred in Brevard.
Rose said wildlife officials were able to rescue, rehabilitate and release 15 manatees that were sickened by this year's Gulf Coast red-tide outbreak.
"Their risks are accelerating. Those risks to their habitat - seagrass loss and strains on the aquifer and the springs - are actually getting more alarming moving forward," Rose said of the species.