In Florida, wildlife managers and environmental groups are stunned by a record number of manatee deaths. More than 750 manatees have died since the beginning of the year, the most deaths ever recorded in a five month period. Most of the deaths are in Florida's Indian River Lagoon, where a large die-off of seagrass has left manatees without enough to eat.

Indian River Lagoon isn't actually a river. It's a large estuary bounded by barrier islands on Florida's Atlantic coast, extending more than 150 miles from Cape Canaveral to Stuart. For years, there have been concerns about declining water quality in the lagoon, caused by a number of factors including development, septic systems, storm water runoff and warming temperatures from climate change.

The lagoon's tipping point

Those problems culminated in 2011 when an algae super bloom covered more than 130-thousand acres of the lagoon's water, blocking the sunlight and causing a massive die-off of seagrass. "In hindsight," Ryan Brushwood, a local biologist says, "it probably was the tipping point."

The lagoon saw algae blooms earlier this year in January. Brushwood, who works for a company that plants seagrass in the estuary, says, "When those blooms were really bad, you couldn't see your hand below the surface. There wasn't a lot of light getting to the plants."

Manatees love Indian River Lagoon, and for years it provided them with lush seagrass to eat. That's not the case now. Chuck Jacoby, an environmental scientist with the regional water district has monitored the seagrass decline. Over a 10 year period, he says, "There's been a decrease of about 46,000 acres." That's a 58% decline of the total acres over the decade.

Indian River Lagoon is a special and fragile place. It's one of the most biodiverse estuaries in the Northern Hemisphere, home to 35 species that are endangered or threatened. Nearly a third of Florida's manatees spend some time in the lagoon each year, but the large die-off of seagrass has left them without enough to eat.

Jon Peterson heads rescue operations at SeaWorld in Orlando. Since December, his staff has been busy responding to the large numbers of sick and dying manatees.

"It's really eye-awakening when you watch what's going on," he says. "You have animals that are out there floating high to what you would, in a normal year, you would think it's a punctured lung from a boat strike. What it's turning out to be is a starvation event."

An "Unusual Mortality Event" that may be far from over

The high number of manatee deaths this year led the U.S. Fish and Wildlife Service to designate it an "Unusual Mortality Event" and open an investigation. The entire population of manatees in Florida is estimated at no more than 6,800.

"When you're talking [about] a population like that and you have a loss of 700 in the first quarter of the year," Peterson says, "it's a very scary look right now."

SeaWorld is one of four facilities in Florida that rehabilitates sick and injured manatees. His staff is caring for 28 of them. Ten are so weak, they're getting nutrition through feeding tubes. Because the manatees have lost so much weight, rehabilitation takes longer than usual.

"You're talking an animal that's down ... 400, 500 pounds," Peterson says. "It will take us three to five months to put that weight back up there to get them to a point where we can release them."

Manatees don't do well in cold water, which is why they congregate during the winter months in Indian River Lagoon and other warm coastal areas. Now that it is warming up, scientists say manatees are beginning to disperse to other areas along the Gulf and Atlantic coasts where they may find ample seagrass. But by late fall, they'll return again in large numbers to familiar waters, including the lagoon.

Michael Walsh, an associate professor at the University of Florida who specializes in aquatic animal health, is worried this mortality event may be far from over. "We have a compromised system that the animals have to utilize and stay in," he says, "but the food is not there in the same amount it used to be."

Manatees need a large-scale restoration effort

The key to helping manatees, Walsh and other scientists say, is to get the Indian River Lagoon healthy again. That will take years, maybe decades, but there are signs of progress. Florida just allocated a half billion dollars to begin phasing out septic systems, a key contributor to the region's nutrient pollution.

In the lagoon, Brushwood's company, Sea and Shoreline, is having success restoring seagrass. Working on a grant from the National Estuary program, Sea and Shoreline planted two acres of a resilient species of seagrass last June. A year later, it's thriving. Similar replanting efforts helped bring back healthy seagrass beds in Crystal River, another manatee habitat in Florida.

Brushwood believes that with enough time and funding, a large-scale effort could bring seagrass back in Indian River Lagoon and tip things back in favor of the manatees.