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Red Tides a Danger to Sea Life
New research suggests that toxic red tides may be responsible for fish and dolphin deaths, even when it's no longer present in the coastal waters.
MELISSA BLOCK, host:
Scientists may have a new answer to their questions about another environmental phenomenon. Marine biologists have long wondered why dolphins, whales, manatees and other marine mammals sometimes die suddenly in large numbers. In some cases, toxic algae blooms, or red tides, are responsible for these deaths; scientists have known that for some time. But new research suggests the threat posed by these toxic tides lingers long after the waters have cleared. NPR's John Nielsen has more.
JOHN NIELSEN reporting:
In the spring of 2004, an especially ugly toxic red tide fouled the waters off the Florida Panhandle. It triggered massive fish kills and lasted for months. Then, just after the waters cleared, a strange thing happened. A hundred and seven dolphins that had seemed to stay away from the worst of the red tide suddenly beached themselves, along with a large group of critically endangered Florida manatees. Scientists called in to investigate assumed that they'd find no link between the vanished red tide and the strandings. Then they sampled local sea grass beds. Jerome Naar, a red tide expert with the University of North Carolina at Wilmington, says the grasses were unexpectedly thick with red tide toxins.
Mr. JEROME NAAR (University of North Carolina at Wilmington): Inside, the toxic can stick under the grass, attach to the sea grass. And then manatees, even as the red tide is gone, can still be exposed to the toxins.
NIELSEN: In the current issue of the journal Nature, Naar reports that the manatees fed on the contaminated sea grasses. He says that's what killed them. He adds that dolphins don't eat grasses and that they wouldn't touch a fish killed by a toxic tide. But Naar also says that dolphins ate fish that survived the red tide, and those fish weren't exactly clean.
Mr. NAAR: Pretty much all the fish present were highly toxic.
NIELSEN: Naar says that's how the red tide toxin moved up through the food chain, building up in the bodies of dolphins until it killed them.
The finding that the toxins link to red tides linger long after the blooms themselves are gone may make it easier to protect at least one of these species: manatees. Naar says there may be ways to herd the giant sea cows away from water they might not recognize as toxic. Leanne Flewelling, a red tide expert with the state of Florida, says recent advances have made it easier to spot red tides before and after they bloom.
Ms. LEANNE FLEWELLING (Red Tide Expert): We sample a lot more now than we used to. We have the benefit of satellite imagery to help us locate blooms. So, you know, we're looking for it. We know how to look for it better.
NIELSEN: On the other hand, there are plenty of questions about the relationship between die-offs and red tides that may never be answered, she says.
Ms. FLEWELLING: Yeah. A big question is: What is a lethal dose? And we still--you know, because they're protected species, obviously, you can't be testing them to figure that out. So that's a big question that we may never know the answer to.
NIELSEN: Red tides don't just threaten wildlife, Flewelling adds. Tourist communities suffer when dead fish wash up on their beaches, and shellfish harvesting businesses lose millions of dollars when their beds are declared unsafe. John Nielsen, NPR News, Washington.
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