HERALD TRIBUNE
April 22. 2007

Red tide poisons food of sea cows
Even after noxious algae dies off, toxins left in sea grasses can kill manatees.

by Kate Spinner kate.spinner@heraldtribune.com

http://www.heraldtribune.com/apps/pbcs.dll/article?AID=/20070422/NEWS/704220314/-1/xml

When 27 manatees died from red tide poisons near the Caloosahatchee River in March and April, there were no signs of a red tide bloom. But toxins from an earlier bloom settled into sea grass beds near Fort Myers, and the grasses stayed poisonous for weeks. As the weather warmed, manatees migrated out of their river wintering grounds and ate the deadly grass.

Because scientists are just beginning to realize that red tide can render sea grass toxic weeks after a bloom passes, few solutions have been proposed to make spring migration for manatees less deadly. "It's really a dangerous time now," said Jan Landsberg, a marine scientist at Florida Wildlife Research Institute.

Manatees frequently perish when a red tide bloom creeps into Charlotte Harbor's estuaries during their spring migration, but it's unusual for so many to die in the absence of a bloom, said Leanne Flewelling, a scientist with the Florida Fish and Wildlife Conservation Commission.

The last time that sort of event happened was in 2002, when 30 manatees died between March 10 and April 30, weeks after an intense February bloom had dissipated.

The only possible culprit in both cases was tainted sea grass, because the red tide bloom had gone away. "When there's an actual bloom present, then there's all different routes of exposure," Flewelling said. With the help of researchers such as Flewelling, scientists have begun to realize that sea grasses can remain poisonous to marine life for weeks, even months, after red tide has passed.

Flewelling's tests showed that sea grasses near the mouth of the Caloosahatchee retained lethal amounts of toxin for weeks, at least into early April. The manatees died over a three-week period, starting on March 14. Necropsies show the animals probably died quickly, said Ken Arison, a biologist with the state's marine mammal pathology lab. The persistence of toxins in sea grass adds complexity to a question that already confounds scientists -- how to keep red tide away from manatees.

Landsberg introduced a proposal to push salt-loving red tide algae out of the Caloosahatchee River with water from Lake Okeechobee last summer at a conference on harmful algae. But in drought years, the lake has little water to spare. And if grasses stay toxic for weeks, a flush might not do much good.

The Caloosahatchee is one of the most popular winter refuges for manatees in the state. More than 400 at a time have been counted near the warm outfall of a power plant on the river east of Fort Myers.

It is also a river vulnerable to extreme fluctuations in salinity. When red tide is present near shore in the dry season, the toxic algae can start to proliferate in the river. Red tide algae usually thrive in oceanic waters, not rivers and bays.

The algae naturally produce deadly chemicals called brevetoxins. Fish are usually the first victims of a bloom, but the poisons go on to kill birds, dolphins and manatees.

Red tide is such a unique threat to the approximately 1,000 manatees in Southwest Florida that a state report last year predicted their numbers would drop 80 percent in three generations. The same report recommended reclassifying the manatee from endangered to threatened, because they are faring better in other parts of the state where red tide is rare.

Federal scientists also reported last month that manatees no longer meet the criteria for a federally endangered species. It could be years before the animal is downlisted federally and months before it is officially reclassified in the state. In a seeming contrast to the reports, a record 417 manatees died in Florida waters last year, about 50 due to red tide exposure in the summer and fall.

Scientists have long suspected that the manatees die from red tide by consuming the toxins. Years ago, however, they thought manatees got exposed by eating sea squirts, which often inhabit grassy areas and accumulate toxins similar to shellfish. Flewelling said her research is showing that the chemicals either cling to the grasses or become absorbed by them. Sea squirts could still be a factor, she said.

Flewelling and Landsberg said research is concentrating on how manatees get exposed to red tide and why they end up dying. Once scientists grasp the problem, more research might be directed at keeping the animals out of harm's way.

Patrick Rose, executive director of Save the Manatee Club, said there are a couple commonsense solutions. Wildlife officials could more aggressively locate animals in distress and rehabilitate them to keep them from dying. He also said that reducing pollution from fertilizers, septic tanks and sewers could help keep red tide at bay.

Some scientists say nutrient pollution is contributing to long-lasting blooms that stretch into the dry season. "There's getting to be more and more evidence that man-induced pollution might be actually making red tide worse," Rose said. "If that is the case, they could go to work on reducing pollution levels in the Caloosahatchee and other water bodies."