Deaths of manatees in lagoon a mystery

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Manatees are drowning for some mysterious reason, with bellies full of seaweed as one of the only clues.

At least 55 manatees have died in the Indian River Lagoon since July, including 25 of them in the past month, mostly in Brevard.

Their carcasses appear otherwise healthy, but their guts are filled with thick drift algae, also called macroalgae, and not so much of their usual seagrass staple diet. That stringy stuff is virtually nowhere to be found in the lagoon, after a phytoplankton explosion decimated the estuary’s seagrass in 2011.

Scientists have yet to identify any known algae toxin that may be killing the manatees.

But biologists with the Fish and Wildlife Research Institute in St. Petersburg say the 2011 phytoplankton “super bloom,” as well as a severe brown algae bloom after that, may have contributed to the manatee die-off.

“So far we haven’t found evidence of disease or viruses at this point, but we’re still looking into that as well,” said Kevin Baxter, a spokesman with the Fish and Wildlife Research Institute.

Baxter said the manatees show “indications of shock and drowning,” so something is affecting their ability to surface for air.

The manatees are not emaciated but have lots of drift algae in their guts.

“That has been a common thread that there have been large amounts of it,” Baxter said. “They’ve generally been healthy looking, otherwise.”

Drift algae can feed off nutrients from fertilizer runoff, septic tanks and other sources, clogging out seagrass, the manatees main food source.

Florida wildlife officials have notified the National Oceanographic and Atmospheric Administration, to determine whether the manatee deaths meet the criteria for that federal agency to investigate them as unusual.

The St. Johns River Water Management District had already planned to survey lagoon drift algae, which crashed in 2010 after cold snaps, leaving behind nutrients for an unprecedented lagoon-wide phytoplankton explosion that killed off most of the seagrass.

“We think that may have been a big cause of the microalgae bloom in 2011,” said Troy Rice, director of the district’s Indian River Lagoon program.

“It’s never come back since 2011,” Rice said of the lagoon’s seagrass. “It’s not good at all, it’s in very bad shape right now.”

A red tide lingering off Southwest Florida since September has killed a record 184 manatees so far this year. But no other significant fish kills, algae blooms or other toxic events that could kill birds have been reported recently in Brevard.

Baxter said that so far there is no indication that the manatee deaths are connected to more than 100 pelican deaths in Brevard County over the past two months. Test results are pending.

The pelicans come in emaciated and with heavy parasite counts.

Biologists had suspected botulism but that generally kills birds quickly, leaving little time for the pelicans to become emaciated.

Dead cormorants, a few bottlenose dolphins and redfish also have been reported recently in Brevard.

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