Florida's manatees are dying at unusually high rates this year, and experts are warning that the sustained loss of a key food source is severely threatening the iconic marine mammals.
The Florida Fish and Wildlife Conservation Commission's most recent report, which spans Jan. 1 to May 28, recorded 761 manatee deaths so far in 2021. Researchers say this year's alarming die-off could surpass the record 804 manatee deaths that were tallied in 2018.
"If this continues through the rest of the year, this is going to be one of the highest mortality years ever," said Jon Moore, a marine biologist and oceanographer at Florida Atlantic University in Boca Raton.
Moore said the main issue is worsening water quality in Florida's waterways from wastewater contamination and nutrient runoff that trigger toxic red tides and overgrowths of algae, known as algal blooms. These recurrent problems are killing off seagrass, seaweed-like plants that grow underwater and are a main food source for manatees.
"The algal blooms are clouding the water and cutting off light, so the seagrass can’t photosynthesize and sustain themselves," Moore said, adding that manatees face starvation and malnourishment as a result.
In the Indian River Lagoon, a 150-mile estuary along Florida's Atlantic coast where manatees are known to forage every year, scientists have recorded a devastating loss of seagrass. An estimated 58 percent of the lagoon system's seagrass has been wiped out since 2009, according to the St. Johns River Water Management District.
Algal blooms are caused by the rapid growth of microscopic organisms and typically generate dangerously high levels of toxins in the water. Algal blooms can occur naturally, but nutrient pollution from toxic wastewater, fertilizers, stormwater runoff and other contamination sources can intensify outbreaks of algal blooms — and make them more frequent.
Decades of nutrient pollution are compounding the environmental stresses on Florida's fragile ecosystems, said Patrick Rose, executive director of Save the Manatee Club, a nonprofit that was established in 1981 by singer Jimmy Buffett and former Florida Gov. Bob Graham.
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"River systems and lagoons can absorb these nutrients to a degree, but once you pass a tipping point, we start to get these massive algal blooms," Rose said. "This shows that we need to completely re-examine how we grow and develop sustainably."
Part of that overhaul will require bolstering systems to process human waste to prevent nutrients such as nitrogen and phosphorous from leaching into waterways, Rose said.
"If we don't take care of our human waste stream, it won't just go away," he said. "These natural systems can only absorb so much before they begin to fail, and in these cases, fail catastrophically."
Manatees were considered "endangered" by the U.S. Fish and Wildlife Service, but a politically contentious decision in 2017 changed the animals' conservation status to "threatened." The alarming number of manatee deaths recorded this year may force officials to rethink that classification, Moore said.
"This year's mortality event may require greater protection for manatees, and we might need to bump them back up into endangered status," he said.
Scientists are also concerned about potential ripple effects throughout Florida's ecosystems. Algal blooms don't just affect manatees: They can also impact crucial fisheries and other marine habitats.
"Rays feed on seagrass, as well as turtles," Rose said. "This will also affect different species of fish, and the fish that feed on those fish. It's something that will affect the entire food chain. When these systems collapse, it gets pretty ugly."