Large numbers of manatees are dying on both coasts of Florida.

In the southwest, a persistent red tide in the Gulf of Mexico has killed nearly 200 manatees this year. These tides are algal blooms, and occur when microorganisms called dinoflagellates proliferate, staining oceans and releasing toxins into the water and air. Harmful to organisms including fish, manatees and humans, the toxins attack the nervous system, causing short-term memory loss, paralysis, seizures and ultimately death.

In the east, near Cape Canaveral on the Atlantic Ocean, manatees are also dying. But there the cause is unknown.

“There are indications of the animals being otherwise completely healthy – but having died of shock and drowning,” said marine mammal biologist Ann Spellman, with the Florida Fish and Wildlife Conservation Commission, the state agency tasked with the investigation.

In July 2012, manatees started turning up dead in the Indian River Lagoon; now, there are 80 dead animals, 50 of them since the beginning of February.

“They’re all dying from a cause that we suspect is a common one – common to those manatees – but right now, is still unknown,” said Kevin Baxter, spokesman for the Florida Fish and Wildlife Conservation Commission.

Alligators aren't a threat to manatees, but microorganisms and boat propellers are. Photo: Patrick M. Rose/Save the Manatee Club

The gentle, blimp-shaped animals, with their bristled snouts and large, fanlike tails, have been on the federal endangered species list since 1967 (.pdf). Scientists estimate that roughly half the world’s West Indian manatees (Trichechus manatus) live in the shallow waters in and around Florida, where aside from microorganisms and mystery killers, the thousand-pound animals are threatened by watercraft, fishing gear and the loss of their warm-water habitats.

Now, the simultaneous mass-mortality events are threatening the state’s manatee population.

“This is very unusual and is unprecedented in magnitude,” said Patrick Rose, a former government biologist and current director of Save the Manatee Club. Rose has studied and worked with manatees since the late 1960s. “This is fast approaching the all-time record catastrophic mortality from cold shock and cold stress experienced in 2010,” he said. During that winter, more than 250 manatees died. “The difference here is that by this time, the cold stress issues were abating with the arrival of spring – and we don’t know when either of these unusual mortality events will extinguish.”

Red Menace

Red tides have thrived for as long as people have kept records of Florida’s seas, with centuries-old descriptions of fish kills and human illness. Now, Florida’s west coast sees a bloom almost every year, Baxter said, though the duration and location are hard to predict in advance. The last time red tide-related mortality was this high was in 1996, when 151 manatees were killed by algal blooms.

In September, a red tide began blooming off Florida’s southwest coast. In October, Sarasota newspapers called it the “worst red tide” in years, reporting tons of dead fish along Florida’s Gulf Coast beaches. Biologists and oceanographers tracked the bloom, watching its progress and sampling the stained waters. “This tide has pretty consistently been over 100, 150 miles long,” said Jason Lenes, a biological oceanographer with the University of South Florida. “The average bloom is generally between two and four months, and this one is lasting for almost six months at this point,” he said.

Occasionally, water tests have come back packed with more than 10 million cells per liter. The threshold for a “high” concentration is one-tenth of that. Though not anomalously high, Lenes said the bloom’s concentrations of cells have been sustained for a long period of time.

>'They're not finding them alive. They're finding carcasses.'

The bloom microorganisms are called Karenia brevis, dinoflagellates that thrive in warm water and are photosynthetic. But K. brevis excrete toxins into the water, compounds that attack nervous systems and cause paralysis, seizures and drowning. Brevetoxins are absorbed by shellfish, can lead to massive fish kills, and stick to seagrasses and other plants, contaminating food sources for herbivorous animals like manatees. At very high concentrations, such as those present periodically during the southwest Florida bloom, brevetoxins can also be inhaled by marine mammals and humans.

As of March 21, 193 manatees have died from the tide since January. Recently, many of the manatees recovered have been found in the vicinity of the Orange River, site of a warm-water aggregation spot near a power plant, where the animals go when ocean temperatures are too cold to tolerate.

The Orange River spills into the Caloosahatchee River, which opens into the Gulf. “Right in that mouth area, where they go to get to the river, is one of the areas where the bloom has been persistent,” Lenes said. With the bloom parked near the river's mouth, the manatees upstream are trapped behind a wall of toxic water – an unfortunate collusion of timing and location.

Now, Rose says, the waters are warming and the manatees are heading back out to the sea and brackish estuaries nearer the coast. There, the seagrasses are likely coated with toxins – toxins that will stick to the grasses even after the bloom dissipates.

Rescuers hoping to help manatees have to act fast. Toxins can harm an animal within a few hours, depending on its size and location. Telltale signs of brevetoxins include listing while floating, muscle twitches and difficulty breathing – all signs that, since the beginning of the bloom, officials have been patrolling the waters and keeping an eye out for, Baxter said.

One of the red tide patients at the Lowry Park Zoo. Photo courtesy of Lowry Park Zoo

So far, a dozen animals have been rescued early enough to be helped. The 12 manatees were taken to Lowry Park Zoo in Tampa, where they’ve all recovered. “If we can get them early enough, we can usually get them through it,” said Larry Killmar, the zoo’s vice president for animal science and conservation. “But what’s happening is, they’re not finding them alive. They’re finding the carcasses.”

After they’re admitted, the zoo’s red tide patients – who now have names like “Threepio” and “Cheer” – are given antibiotics and rigged with a buoy system to keep them afloat. Then, staff members sit with the animals until they’re well enough to float on their own. Instead of seagrass, which is difficult to harvest and potentially contaminated, the zoo’s patients are fed romaine lettuce.

A lot of it.

“Manatees eat 10 percent of their body weight in food a day,” Killmar said. “At our peak, with 22 manatees on site, that was 5,200 heads of romaine lettuce a week.”

The animals won’t be released into the wild until the bloom is gone. As of this week, it’s still offshore and in the area of Lee and Charlotte counties, though the concentration of cells is decreasing. But danger lingers even after the blooms have dissipated, since toxins stick to and encrust the seagrasses manatees rely on for food. Just last week, 13 dead animals were recovered near Lee County.

“The good part is, if you can rescue the manatees, there are good methods for eliminating toxins from their system and their recovery is pretty quick,” Rose said. “In contrast, I don’t know of any manatees that have been found alive from what’s happening on the east coast.”

Manatees playing in Blue Spring.

Eastern Mystery

The Indian River Lagoon runs for 150 miles along Florida’s eastern shores. One section, the Banana River, shapes the western bank of Cape Canaveral, near where NASA launches rockets into space.

It’s here, near the Kennedy Space Center, that manatees are mysteriously dying. Since the beginning of February, 50 animals have been pulled from the lagoon’s estuarine waters – that’s more than half of the 80 manatees who’ve died in the area since July.

The killer in the east slays swiftly and leaves behind nary a clue.

"They were big adults, they had good fat storage. But they seem to have died very acutely," said Martine deWit, a veterinarian who oversees the state's marine mammal pathology lab. "Whatever killed them, it happened really fast."

Two manatees found dead in the Indian River Lagoon. Photo: Florida Fish and Wildlife Conservation Commission

Other than being dead, the animals look normal. They’re not starving and show no signs of sickness. Many have bellies stuffed full of macroalgae, including Gracilaria, a nontoxic seaweed, but one that manatees rarely eat. Most look as though they’ve gone into shock and drowned – some so quickly that by the time rescuers respond to calls of a strangely behaving manatee, the animal is dead.

“Some still have intact pieces [of algae] in their mouths,” deWit said.

Without a live, sick animal to monitor, scientists are stuck searching for patterns, playing the roles of forensic investigators and looking for clues.

So far, there’s no easily identifiable affected age or size class. Tests for toxins in the water have turned up nothing. No brevetoxin, no domoic acid, no signs of anything known to kill manatees. The animals’ tissues don’t show signs of viral or bacterial infection, though deWit said a few show minor pathological signs associated with a toxin having entered their gut.

“We have tested for a couple biotoxins that do occur in Florida, and so far those are negative,” she said.

The most obvious links are where the animals are found, and their bellies full of the wrong kind of food.

>'The mechanism has not been identified.'

Scientists suspect the manatees are turning to a foreign food source because their preferred meal, seagrass, is no longer around. Since 2011, two algal blooms have destroyed the lagoon’s invertebrates and grasses. The first was a green algae superbloom; the second, a brown algal bloom that turned the lagoon brown and wiped out 32,000 acres of seagrass. Together, the blooms shaded the water and prevented grasses from growing.

But, “The brown algae causing the death in the sea grasses is not killing these manatees,” said Dana Wetzel, a chemical oceanographer with Mote Marine Laboratory in Sarasota.

On their own, these blooms are harmless. Some suspect, though, that the blooms are fed by nitrogen- and phosphorous-containing nutrient-rich runoff – the wash that flows into the sea from fertilizer-laced lawns, storm drains and septic fields after it rains. Normally, seagrasses would sequester these extra nutrients or metabolize them, keeping the ecosystem balanced. But after the algal blooms kicked off and the grasses died, nutrients flooded the lagoon, fueling further algal growth and concentrating in the water.

How that’s related to manatees’ demise is unclear; scientists are still hard at work trying to figure out what’s going on. “As of right now, the mechanism has not been identified,” Spellman said "We don't necessarily feel that where the animals are dying, the animals are eating." But the fact that so many are recovered from the same place suggests that whatever is going wrong is something local. Wetzel and others say it’s possible a yet-to-be identified biotoxin is circulating in the ecosystem.

Manatees aggregate near warm-water sources; cold snaps, like in the winter of 2010-2011, can kill hundreds of the animals. Photo: Ann Spellman

And there are other signs that the Indian River Lagoon is in distress: As of March 21, 200 dead brown pelicans have been found there this year, emaciated and infested with parasites. But right now, Baxter says, there’s no evidence that pelican and manatee mortality are linked.

It’s possible that something in the lagoon is affecting dolphins as well. Megan Stolen, a research scientist with Hubbs-SeaWorld Research Institute, says teams in the area have recovered a slightly higher-than-normal number of deceased dolphins – four in January, five in February, three so far in March. “A number of them have been emaciated,” she said. “They’re really thin, skinny, and starvation mode.”

But there’s no lack of fish in the lagoon. “It’s not that they’re starving because there’s no fish. If they’re starving it’s because they can’t find food, can’t chase the food, can’t metabolize it,” she said.

So far, though, the numbers aren’t statistically significant – averages for those months are between two and three dolphin deaths – and again, there’s no obvious connection to the manatees’ demise. “I would say we’re on alert,” she said. “But right now, there’s not a reason to be worried.”

What does worry scientists is that there’s no way of knowing when the manatee die-offs in the lagoon will end – or when they’ll know what’s going on.

“That’s probably one of the most disturbing things,” Spellman said. “If this were a cold snap, we’d know. Right now, we don’t even know what to look for. They’re not even showing any outward signs. We have no idea when this will end. “