Deadly Algae Bloom Known as “Red Tide” Killing Hundreds of Manatees

- Thursday, April 04, 2013

Series Producer Marsha Walton provides a very sad update on Florida manatees. 

The past few months have been excruciating for the scientists and volunteers who work with Florida’s manatees. Instead of documenting which animals have returned to their winter homes, and which moms have new babies, they are instead retrieving the bodies of hundreds of animals killed by deadly red tide.

“Several things are happening,” said Patrick Rose, a retired state biologist and current director of Save the Manatee Club

“The worst is red tide in southwest Florida, from Bradenton south to Lee County. We are closing in on 200 manatees dead from that event alone,” Rose told “This American Land.”

How does red tide kill these giant, plant-eating mammals?

The red tide organism is a phytoplankton, or algae, known as Karenia brevis. While it is always present in the Gulf of Mexico, on occasion it reproduces wildly, or “blooms,” sometimes covering more than 100 miles. It can discolor water and poison fish and other wildlife. Warm waters can trigger these blooms; scientists believe pollution and agricultural runoff may also feed the algae’s dramatic growth. 

For the manatees, red tide brings excruciating suffering. When the red tide organism dies, it gives off a toxin. The dead algae settles into the sea grasses that the manatees eat, and the toxin causes seizures and a lack of coordination. The animals drown because they can’t keep their heads above water.

The red tide that started in September 2012 is described as one of the worst in years, not only affecting manatees but leaving tons of dead fish along Florida’s west coast beaches. It’s also lasted longer than normal, now more than six months, and has stretched at times to 150 miles long.

Since knowledge of this season’s severe red tide, some manatees have been rescued and are being rehabilitated.

Rose says if rescuers can get to the manatees, even if they are infected, they can recover quickly. They must be stabilized, and then kept out of areas that still have active red tide outbreaks. Saving the animals literally involves keeping their heads above water, truly a challenge when they can weigh a ton or more. 

If you saw our story on the manatees of Crystal River, Florida in our second season, you saw what amazing, if odd-looking animals these are. Our host Caroline Raville and photographer and producer Jim Gilson did some terrific reporting on the population that spends the winter at the Crystal River National Wildlife Refuge. 

Rose says pollution and water quality issues are a big part of what’s led to red tide. High levels of nutrients in Florida’s hot climate can lead to an algal bloom. Excessive nutrients can result from agricultural runoff, discharge from water treatment facilities, stormwater from streets and from residential lawns.

While much progress has been made in educating boaters about propellers harming manatees, outreach is also needed for these long- term killers as well. 

“We need to prevent this from happening in the first place,” said Rose. “We need to deal with pollution, flows from power plants, use permits --from beginning to end,” he said.

Complicating the crisis is another, unknown manatee killer on Florida’s east coast. Dozens more manatees are dead, and biologists have not yet determined the cause. All have drowned after eating large amounts of a macro-algae, and their deaths may be tied to a change in their diet. 

The Florida manatee population is believed to be just over 4,000. They have been on the Endangered Species List since 1967. 

If you should spot a sick or dead manatee, please call the Wildlife Alert Hotline at 888-404-3922. That number is staffed 24 hours a day, so don’t hesitate to call if you see a distressed animal.

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