Mysterious manatee syndrome pops up again

MELBOURNE — At least nine manatees in Brevard County have died since May from the return of a bizarre syndrome that first began killing seacows in 2012 when widespread seagrass dieoffs forced them to change their diets.

Seacows have been gobbling up a stringy seaweed that drifts in the Indian River Lagoon like "tumbleweed" does in the desert, lining the lagoon banks and fouling the air.

Officials can't pinpoint exactly what about the change of diet is leading to the deaths.

"It appears that the nutritional value itself may not be a problem," said Martine deWit, a biologist with the Fish and Wildlife Research Institute. "The suspicion is that there is a different composition of the diet that makes the animal susceptible to complications."

All nine dead manatees — the last one on July 4 — were found in the Melbourne area, she said.

The carcasses come in to the Fish and Wildlife Research Institute in St. Petersburg with stomachs full mostly of seaweed, instead of the manatee's usual staple diet of seagrass.

Manatees have been eating more of the thick seaweed-like drift macroalgae, because microalgae blooms have choked out their usual seagrass diet. Scientists had suspected a toxin that affects the seacows' nervous system was hampering the marine mammal's ability to surface, causing it to drown. But several typical algae toxins have not shown up in testing.

DeWit likens the mysterious manatee syndrome to when people visit foreign countries and get sick from the food or water.

But scientists say they're still stumped as to why.

"Whatever causes their gut (to get) upset makes such a chain reaction in the body that they acutely react to that," deWit said. "We have lots of pieces of the puzzle that we're putting together ... The majority of the animals are eating this and survive."

The mysterious deaths began to happen in Brevard in mid 2012, killing more than 100 manatees.

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In moderation, drift algae is good, providing food and cover for marine life and sponging up excess nutrients from the water. But too much can choke out seagrass.

Drift algae has entangled the lagoon in a boom-and-bust cycle in recent years, leaving the estuary with too much or too little.

In 2010, Nova Southeastern University used an acoustic sensor to survey the lagoon's drift algae from Titusville to Sebastian Inlet. They found drift algae had increased by 46 percent in two years, to 102,162 metric tons over the 109 square-mile study area.

Contact Waymer at 321-242-3663 or jwaymer@floridatoday.com. Follow him on Twitter @JWayEnviro

To report a sick or dead manatee or other wildlife, call FWC's toll-free hotline: 1-888-404-FWCC (1-888-404-3922) Cellular phone customers: *FWC or #FWC