Florida's beloved manatee is having a devastating year. More than 749 manatees have died since the start of 2021, a number some longtime advocates fear could grow to over 1,000.

Manatees are dying in droves this year. The die-offs could spell trouble for Florida

Updated 6:51 AM ET, Sun May 30, 2021

(CNN)Despite their portly frame and inherent meekness, Florida's manatees are survivors.

When power plants began popping up along Florida's East and West coasts, manatees learned to follow the flow of the unseasonably warm water.
When boats with sharp motors increasingly flooded their habitats, they learned how to live with debilitating injuries, or tried to.
And when their favorite source of food began to disappear when toxic algae infested the water, they learned to eat less, often at the cost of their health.
Their gentle nature belies a deceptive resilience. Unathletic as they may seem -- they tip the scales at around half a ton -- they're built to endure.
But how much more can one species take?
When manatees are malnourished, they can lose weight toward the back of their heads, giving their face a distinct peanut-like shape.
Decades of environmental stress culminated this year in one of the worst manatee die-offs in recent history: As of May 21, at least 749 manatees have died in Florida in 2021, in what the Florida Fish and Wildlife Conservation Commission has called an unusual mortality event, or UME.
Manatee advocates who've sounded the alarm for years saw it coming.
"Manatees are literally that sentinel species," says Patrick Rose, executive director of the Save the Manatee Club, a 40-year-old nonprofit co-founded by Jimmy Buffet. "They're warning us of what else is going to come if we don't do a better job while there's still time to do something about it. If we don't, our own lives will suffer."
Florida, the third-most populous state in the US and still growing, stands to lose more than its state marine mammal if manatees go extinct. The same issues that have caused their mass deaths are disrupting freshwater and saltwater sanctuaries, killing off fish and other species and mucking up the water that millions rely on for their livelihoods. Florida beaches are now as well known for red tide as they are for pristine white sand and watercolor sunsets.
Rose thinks around 1,000 manatees could wind up dead by the end of the year. If manatees continue to die at such a rate, with an estimated 7,500 animals left in the wild (before factoring in this year's deaths), it could be only a matter of years left to save them -- and clean up Florida's water.

A sea of problems faces manatees

West Indian manatees had been on the mend for many years before their fortunes changed. Their recovery from near-extinction in the 1970s to a population over 7,000 was heralded as a victory for conservation. The US Fish and Wildlife Service, in a decision that proved controversial, even downlisted the West Indian manatee from endangered to threatened in 2017 due to the major population gains.
But problems had been bubbling below the surface for decades, and in 2021 it seems they've boiled over. The stressors facing manatees are numerous and entwined, and one can't be conquered without addressing the other, said Michael Walsh, a clinical associate professor at the University of Florida College of Veterinary Medicine who specializes in aquatic animal health.
The trouble, Walsh says, begins in the water.
When nutrients from wastewater or runoff containing fertilizers, microplastics or toxic chemicals leach into a manatee's marine habitat -- whether freshwater or saltwater -- they can throw off the balance of the water and cause harmful algae blooms to form.
Boats were once manatees' most fearsome foe. These days, they're one of many.
The blooms blanket the surface of the water and shade out the seagrasses underwater that rely on the sun to survive, killing the grasses.
The seagrasses that survive the malevolent blooms are then overgrazed by manatees whose sources of food have shrunk, so the plants can't quickly regrow and continue to feed the manatees, Walsh said.
And when seagrasses die, gone is the manatee's favorite food source. They may start to nosh on other plants that don't fortify them the same way, or make do with less food (manatees should eat somewhere around 10% of their body weight per day, which translates to about 100 pounds of grass for an 1,000-pound adult manatee) and begin to lose weight. Over time, this leads to malnutrition and, eventually, starvation, Walsh said.
While climate change is generally warming water temperatures, warmer temperatures can foster the growth of harmful algae, which may kill seagrasses in their favorite warm water oases. So manatees may travel hundreds of miles until they find a new source of food and, hopefully, warm water. But the colder it gets, the more food they'll need to consume to stay warm, Walsh said. If there's less food, they'll succumb more quickly to cold stress -- for their impressive girth, they don't have enough blubber to keep themselves warm when the water temperature drops below 68 degrees Fahrenheit.
What's more, manatees have learned to rely on the warm water outflows from power plants on both coasts of the state -- about two-thirds of all manatees stay warm this way, according to a 2013 estimate. If those plants close as the state transitions to more sustainable energy sources, manatees will lose a reliable haven for warmth, leaving them with few options for wintering, Rose said.
There's also the problem of people: Florida has around 21.4 million residents, according to a 2019 Census Bureau count (a figure that may be higher now, given the number of Northeastern expats who moved down during the pandemic). Couple unimpeded population growth with an infrastructure system the American Society of Civil Engineers described as "deteriorating," and the pressure on water treatment systems in the state can be debilitating.
Manatees crowd together near the warm-water outflows from Florida Power & Light's plant in Riviera Beach, Florida, in February.
"Add up starvation, together with red tide, severe cold weather mortality ... these are just absolute catastrophic losses that they may never be able to recover from," Rose said.
Just under 90 manatees have been rescued in 2021 so far, according to the Florida Fish and Wildlife Conservation Commission. But most manatees who've died have not been necropsied, and some of their bodies were too decomposed to study, according to the commission's preliminary mortality report for the year.
The last comparable unusual mortality event occurred in 2010, when temperatures in Florida fell to historic lows in a cold snap that proved extremely dangerous for manatees. More than 760 manatees died that year, according to the FWC.
But 2021's count is already approaching that number, and the year isn't even halfway through.

What went wrong in manatees' favorite habitat