Researchers Find Pond Scum Toxin that May Kill Bald Eagles
LOCATION Two researchers at the Hollings Marine Laboratory on James Island have made what could be a groundbreaking discovery in the search for a mysterious killer of bald eagles.
Four years into their work at the Fort Johnson facility, researchers Susan Wilde and Sarah Habrun said they think a previously unknown form of pond scum carries a toxin that's killed some 100 of the majestic national symbols in the Southeast, including half the nesting population in the Thurmond Reservoir on the South Carolina-Georgia border.
If the duo are correct, their "eureka moment" could help thwart a strange new avian disease. Wilde, a University of South Carolina assistant professor, observed an unidentified blue-green alga that grows on hydrilla, an invasive plant species that clogs state waterways. Habrun, a research technician and College of Charleston graduate student, grew a culture of the pond scum in late 2004 after three years of being daunted by blooms of other blue-green algae that crowded it out of lab samples.
Field tests showed mallards that eat the algae develop avian vacuolar myelinopathy, a brain-eating disease. The eagles apparently get it from eating coots. Ducks and geese also have died from the disease.
"If we're right," Wilde said, "we're talking about a totally new species and a new neurotoxin traveling through the food chain."
Blue-green algae, the ubiquitous slime that blooms in still water, often is harmless enough that some organic advocates tout it as a food supplement, although researchers have found a number of toxins can grow in it.
The hunt for AVM has been "one of those studies where you have no idea what's going on initially," said Tom Murphy, the state Department of Natural Resources biologist who asked for help from Wilde, an algae specialist.
One by one, pesticides, mercury, infectious disease and known toxins were ruled out as causes of AVM. Wilde got involved because of "the really long shot" that an unknown algae toxin might be the culprit. The 16-year algae research veteran, fondly referred to as "the pond scum expert" by her in-laws, grew up in a family in which her veterinarian dad took the children on walks and taught them the scientific names of trees. Even today she is fascinated with knowing names.
Habrun applied for a job at the lab when she enrolled in the college to work on her master's degree in environmental science. As a kid, she'd always loved cutting things apart in biology lab.
The researchers are cautious about overstating the impact of their work, but they are excited. "I don't know if I can ever expect to do something like this again," Wilde said.
Other toxins have been found in pond scum, suspended in the water or growing on the bottom. Wilde found this alga growing on the underside of hydrilla leaves underwater.
The "eureka moment" came for the two researchers when they peered at the culture through a microscope. Wilde said she knew they had something "as soon as I turned on the fluorescent light and saw the glowing red balls in filaments." Gene sequencing determined it was, indeed, a new species.
AVM is considered the most significant unknown cause of eagle deaths in United States history, according to the National Wildlife Health Center Web site, which describes it as a mysterious disease whose cause has eluded scientists.
It first was discovered in 1994 when 29 bald eagles died in Arkansas. On the South Carolina-Georgia border, 17 eagles were killed by AVM at Lake Thurmond and the Savannah River Site in 2000-01.
The disease has been found at Lake Murray but not Lakes Marion or Moultrie. The algae apparently don't grow on hydrilla close to the coast.
The researchers now must figure out what water, weather, light and nutrient conditions make the algae grow, then do field studies. If the blue-green alga is the culprit, the cure is simple. "You can get rid of hydrilla," Wilde said.
The threat to the national symbol is a powerful argument for stepping up control or removal of hydrilla in areas where the algae can grow. Aquatic plant professionals are watching the work closely, Murphy said.
AVM hasn't stopped the bald eagle's remarkable recovery in South Carolina and the Southeast, at least not yet, Murphy said. The number of eagle pairs nesting in the Palmetto State has risen from 13 in 1977 to 190 this year.
But because the disease is emerging, nobody knows about its long-term effects. It can take decades for the eagles to re-establish a nesting population in any one location.
Source: Knight Ridder/Tribune Business News