Manatees that survive exposure to Red Tide algae blooms may wind up with compromised immune systems, making them more susceptible to disease and other woes, a new study finds.
The discovery may alter the way the survivors are cared for at Tampa's Lowry Park Zoo and other rehabilitation facilities around the state.
Earlier this year, more than 270 manatees along the state's southwestern Gulf Coast died from the toxins in a Red Tide bloom — the worst die-off since records began being kept in the 1970s.
A handful of manatees that survived were tested by Mote Marine Laboratory in Sarasota. The Mote scientists collected blood samples from 13 manatees being treated for Red Tide exposure at Lowry Park Zoo, according to Cathy Walsh, manager of the marine immunology program at Mote Marine Laboratory.
For comparison purposes, the Mote researchers also collected blood samples from wild manatees in Crystal River, where the Red Tide bloom had not shown up at all.
The Mote scientists then tested the blood to see if one type of immune cells, called lymphocytes, multiplied the way they normally would when a manatee's body is challenged by infection.
They found that when the Red Tide toxins are still in the manatees' bloodstream, the lymphocytes did not multiply the way they normally would.
They also found that the manatees' blood plasma had higher levels of the types of molecules the body produces during stress. And they found increases in an enzyme that signifies stress on the immune system.
That means that even after the manatees appear to be recovered from exposure to the Red Tide, they remain more vulnerable to diseases and other problems, including cold, that could kill them. But no one knows yet how long that could last.
"We can't really answer how long the lingering effects go on," Walsh said. With sea turtles, though, scientists have found that Red Tide toxins may stay in their bodies for up to 80 days, she said.
The Mote study, unveiled at a recent conference at Mote, "provides some new insights into the long-term health and survival for rehabilitated manatees that have recovered from clinical Red Tide exposure," said Ray Ball, Lowry's director of medical services. "This may redirect the medical care while they are in rehab and also provide new criteria for release."
Red Tide is a higher-than-normal concentration of microscopic algae. The blooms stain the water a rusty tint and can kill fish, manatees, dolphins and other marine creatures. The algae contains at least 12 toxins that can also be harmful to humans, particularly those with respiratory problems.
Red Tide has plagued Florida's beaches for centuries. Spanish explorers recorded blooms in the 1500s. Karenia brevis — named for retired biologist Karen Steidinger, who spent decades studying its properties at the state's marine science laboratory in St. Petersburg — lives in the Gulf of Mexico all year long, usually without causing any problems.
But every now and then the algae population just offshore explodes into something called a bloom, staining the water a rust color and releasing large amounts of toxins. Pollution does not appear to affect the start of an offshore bloom, but can stimulate its growth and prolong it once it moves inshore.
The bloom that killed so many manatees this year appeared last fall along 70 miles of the southwest Florida coast, extending along the shores of Sarasota County south to Lee County, and hung on until March.
In the past, Red Tide has killed manatees because they breathed in its toxins when they surfaced for air. This year biologists said manatees had consumed the toxins after it settled onto sea grass they ate.
Craig Pittman can be reached at firstname.lastname@example.org or on Twitter @craigtimes.