New evidence confirms a strong connection between toxic Pfiesteria piscicida and water polluted with animal or human waste, top experts said at a scientific meeting in Baltimore yesterday.
Since 1997, when the rivers of Maryland's lower Eastern Shore suffered their first known outbreaks of the microorganism that can kill fish and make people sick, scientists have strongly suspected a link between the outbreaks and tainted runoff from poultry manure, spread as a fertilizer on the region's farm fields.
That suspicion led the state to draw up one of the nation's most stringent plans for controlling the flow of nutrient-laden runoff into Maryland rivers and streams, despite protests from farmers and the poultry industry that there was no conclusive proof of the connection.
All the research suggests the link is real, scientists said.
"What's happened over the last few years is there's more and more and more evidence that's consistent with that, rather than evidence that tends to undermine it," said ecologist Donald Boesch, president of the University of Maryland's Center for Environmental Science.
Boesch heads a multistate committee of science advisers that convened yesterday to help the Maryland Department of Natural Resources plan its Pfiesteria monitoring program. This year, the state will concentrate its monitoring, which begins next month, on rivers of the lower Eastern Shore and the coastal bays west of Ocean City. The microorganism was found in some of the bays' most polluted creeks for the first time last year, though there were no toxic outbreaks - fish kills or human illnesses due to Pfiesteria.
In tests in her laboratory at North Carolina State University, JoAnn Burkholder, the co-discoverer of Pfiesteria, has documented explosive growth of the organism's toxic stage when exposed to human sewage or pig farm wastes.
Burkholder's team collected the wastes, decontaminated them to get rid of bacteria, and added the sludge to samples of Pfiesteria in its toxic stage.
The cells multiplied more than 500-fold over a period of five days, Burkholder said. The nutrients in the waste fuel the growth of algae, one of Pfiesteria's favorite foods. As the algae multiplies, so do toxic cells, she said.
Researchers from Maryland's Department of Natural Resources have found a strong correlation between high levels of chlorophyll - the green pigment produced by algae - in the state's rivers and the presence of Pfiesteria.
"As you see higher and higher levels of chlorophyll, you tend to be more likely to see Pfiesteria," said Rob Magnien, a DNR Pfiesteria expert.
"Whether you look at the field data or the lab data, it continues to reinforce the basic concept" of a link between nutrients and Pfiesteria, Magnien said.
That information helps state researchers pin down the areas where Pfiesteria is most abundant. But because the tiny dinoflagellate is benign most of the time and turns toxic only under a complex set of conditions that are poorly understood, it's still very difficult to quickly spot a toxic outbreak, researchers said.
Pfiesteria is widespread in more than a dozen rivers where DNR researchers have looked for it over the past four years.
"There's about a 4 1/2 or 5 percent chance that if you take a water sample on these rivers, you'll find Pfiesteria," said David Goshorn, a DNR ecologist.
There have been no toxic outbreaks since 1997, and the only test for Pfiesteria in water can't tell the difference between its harmless and dangerous stages, a transformation that takes a matter of hours.
Scientists once thought that the presence of menhaden with bloody lesions was a sign that they were being attacked by toxic Pfiesteria. But several researchers have cast doubt on the idea that Pfiesteria causes the lesions and have suggested other causes for the sores. Now scientists wonder whether it's a good idea to use fish with lesions as a warning of toxic Pfiesteria.