Scientists Are Puzzled as Pfiesteria Fizzles
Washington Post Staff Writer
Wednesday, Sept. 23, 1998; Page B01
A summer that many scientists expected would reawaken the poisonous microbe Pfiesteria piscicida and deliver another season of trauma to the Chesapeake Bay instead proved quiet and benign.
A leading scientist said yesterday that lesions found on fish in August in an Eastern Shore creek probably were not caused by pfiesteria, effectively ruling out the one indicator to surface this year suggesting the toxic microbe had returned.
"We do not believe pfiesteria was responsible," said JoAnn Burkholder, an aquatic botanist at North Carolina State University. She cited recent tests conducted at her laboratory, which found no evidence of toxic pfiesteria in water samples taken from the bay tributary, Shiles Creek.
No one is certain why the so-called Cell from Hell failed to make a reappearance this year, though theories abound. Some scientists speculate stormy weather may have scuttled an outbreak, flushing out concentrations of would-be assailants.
Others surmise a scarcity of menhaden deprived pfiesteria of its means of going toxic. Some scientists think dense schools of fish such as menhaden secrete something that triggers the otherwise harmless microbe to turn poisonous.
Despite the microbe's apparent disappearance, some scientists still think pfiesteria has been building in numbers for years, nurtured by pollution washing off the land and salted away in sediments. Though the absence of outbreaks this summer has delivered relief to those who watch the bay, as well as those who take their living from it, scientists say the microbe could just as easily come back next summer.
"It doesn't mean that we're out of the woods," said Dave Goshorn, a marine biologist with the Maryland Department of Natural Resources. "We know pfiesteria's out there. For whatever reason, the conditions didn't come together this year."
While the toxic moods of the bay seem more mysterious than ever, scientists have claimed some progress in mapping out the human illnesses linked with exposure to pfiesteria. A recent article the Lancet, a leading medical journal, buttressed findings by a Maryland medical team that pfiesteria exposure inflicts short-term memory loss.
Meanwhile, a federal study completed this month in North Carolina found evidence of long-term visual disorders in watermen who have worked Pamlico Sound. Pfiesteria is blamed for killing more than a billion fish over the last decade in North Carolina.
At a briefing at the National Press Club yesterday, Burkholder and other scientists discussed the need for more reliable indicators of toxic pfiesteria's presence.
Wolfgang Vogelbein, a researcher at the Virginia Institute of Marine Science, said lesions on fish make for a crude indicator because the lesions can be inflicted by fungal agents as well.
The trouble is, scientists and public health officials don't yet have better indicators. They can tell, after a look through a microscope, whether a particular water sample is likely to contain toxic pfiesteria.
But not until fish are immersed in tanks with cultures produced from the water samples can scientists say with any certainty whether toxic pfiesteria was actually at work a process that takes eight weeks and costs more than $1,000. Burkholder's claims that pfiesteria was not the culprit at Shiles Creek were based on that sort of test.
A new series of tests being developed by Parke A. Rublee, a biologist at the University of North Carolina, would allow scientists to confirm the presence of toxic pfiesteria in water samples within a day.
Some scientists cautioned that pfiesteria still may have been to blame for the lesions at Shiles Creek, despite Burkholder's findings. Just because a test fails to establish a positive connection doesn't mean the connection is disproved, they said. But no one disputes the larger picture: Last year, pfiesteria killed fish and sickened people on four rivers in Virginia and Maryland. This year, it slumbered.
Burkholder suggested the Chesapeake geography is less prone to pfiesteria outbreaks than North Carolina waters, where pfiesteria has returned every year since its discovery in 1988. The Neuse River, at the bottom of Pamlico Sound, scene of North Carolina's worst fish kills, is a largely stagnant estuary that allows nutrients to collect and nurture a host of environmental ills, pfiesteria among them.
The Chesapeake Bay waters circulate about once a month. Except in years when weather conditions are just right, Burkholder said, Maryland and Virginia could slide by without regular outbreaks.
But Donald Boesch, president of the University of Maryland's Center for Environmental Science, said conditions this summer were not markedly different from last. Salinity was about the same. Early rains sent a torrent of nutrients into the water. Though water temperatures were somewhat below normal in the spring, they reached expected levels by August.
"The one explanation that seems to jump out is the relative paucity of menhaden," he said.
© Copyright 1998 The Washington Post Company