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Toxic shocker: the organisms blamed for fish kills are related to Pfiesteria piscicida (above), whose discoverer, JoAnn Burkholder (below), b. lames it for neurological symptoms she has experienced. Credit: KAREN STEIDINGER

A mystery organism which is believed to have killed thousands of fish in Chesapeake Bay, on America's mid-Atlantic coast, and prompted a major public health scare, should become less mysterious within weeks as scientists rush to track down the organism and identify the toxins it releases.

Multi-agency research is already under way to investigate the dinoflagellates, which are thought to have killed some fish and caused large lesions on many others. According to an early study, fishermen who work the infected waters have suffered memory loss and skin problems. The infected fish are menhaden, which is never eaten but is harvested in huge quantities for use in pet-food and as a source of cheap oil for margarine.

But the scientists who pioneered the study of similar organisms claim their investigations have been obstructed by officials in the nearby state of North Carolina, who wanted to protect their tourism, fisheries and agriculture industries from the kind of public attention now developing in Maryland.

The organisms in the Chesapeake — a 200-mile-long sea inlet whose health and conservation is a major public concern in the region around Washington — are closely related to Pfiesteria piscicida, a remarkable single-cell organism first identified five years ago by JoAnn Burkholder of North Carolina State University (see Nature 358, 407; 1992).

Pfiesteria can take twenty or more distinct forms during its life cycle. It can play dead on the sea bed, grow via photosynthesis, secrete toxins, eat the fish poisoned by the toxins, and return to an ambient state — to be branded “the cell from hell” by The New York Times.

“Of all the organisms I know, it's the most complex by a quantum jump,” says Donald Anderson of the Woods Hole Oceanic Institute, Massachusetts. “It's hard to understand how it evolved that way. But if you wanted an organism that would survive for millions of years, that would be a good way to do it.”

Burkholder found that Pfiesteria growth was boosted by the presence of phosphorus in the water, and became embroiled in arguments with North Carolina officials about the role of the effluent from the state's hog-farming industry in the organism's behaviour. Burkholder and Howard Glasgow, her collaborator, suffered neurological symptoms which they attributed to their contact with Pfiesteria in the laboratory. Their story is related in a recently published melodramaFootnote 1.

Ironically, the suspicion that Pfiesteria is a health hazard has slowed down research on the organism. Scientists could not study it unless their laboratories met standards for the containment of biological hazards, which are rare in marine biology laboratories.

But since fish kills were reported in Chesapeake Bay just over a month ago, Burkholder and a few others have won access to medical laboratories for the analysis, and have made substantial progress in identifying the toxins released by Pfiesteria. They have also been adopted as advisers to the state governments confronting the problem.

Burkholder is working with the Medical University of South Carolina to track down a toxin associated with brain damage in fish. Edward Noga, her Nature co-author, has worked with researchers at the University of Miami on a separate toxin that may cause lesions on the fish. “We've made great strides in the past three weeks, thanks to the help of these places,” Burkholder says. “We've isolated a water-soluble toxin and a lipid-soluble toxin, and are very close to finding out what the water-soluble toxin is.”

But Karen Steidinger of the Florida Marine Research Institute, who has been analysing water samples from Chesapeake Bay, says that the two dinoflagellates she has identified are not Pfiesteria. “Once you take off their membrane, they are very different,” she says. Although closely related to Pfiesteria, these organisms could produce different toxins that interact differently with fish and with people, she says.

A study conducted in the past three weeks for the Maryland state government, by a team led by Glenn Morris of the University of Maryland School of Medicine, found a strong correlation between exposure to water near the fish kill and various neurocognitive symptoms. The study compared a self-selected sample of eleven fishermen who worked the Pocomoke river, where a major fish kill occurred in August, with a group which may have received lower exposure, and a third group which works nearby on the Atlantic Ocean and is assumed to have had no exposure at all. “We found a significant problem with memory loss” in the high-exposure group, Morris says. “There do appear to be clear, documentable health effects.”

Steidinger, however, says that the correlation itself does not prove that people have been poisoned by the Pfiesteria-like organisms. The dead fish themselves, she points out, will put toxins in the water: cause and effect can be established only by identifying and tracking the toxins from the organisms.

The Morris study, which was released last week, has been the subject of some disagreement between Maryland and Virginia, the two states surrounding the bay, with the former unwilling at first to hand over its raw data for scrutiny by the latter.

The Democrat governor of Maryland, Parris Glendening, who is up for re-election next year, has sought to impress the largely urban voters of his state by taking immediate, high-profile action on the fish kills. He has closed several rivers to fishing, and obtained federal assistance and pledges of public concern from President Bill Clinton.

Virginia is taking a far more cautious approach. George Allan, its Republican governor, has refused to close any rivers apart from the Pocomoke itself, despite the discovery of fish with lesions in other waterways.

The two men buried some of their differences at a ‘governors’ summit' hosted by Glendening last week in Annapolis, Maryland's capital, at which they agreed a five-point plan to cooperate in addressing the problem. Allan continues to express doubts about the Morris study, however. “The number of people who reported memory loss was, I believe, eight,” he says. “Our medical professionals haven't had the chance to look at it yet. I'd want our folks to look over it and see if they come to the same conclusions.”

A barrage of small-scale federal initiatives was announced last week to pursue the mystery organism. The Environmental Protection Agency (EPA) and the National Oceanic and Atmospheric Administration have sent teams to the bay and will provide Maryland with emergency grants.

The Centers for Disease Control, which is expected to receive an emergency $7-million appropriation from Congress for Pfiesteria research, will host a conference in Atlanta next week to “plan a comprehensive public health approach to Pfiesteria”.

The Food and Drug Administration is expected to explore any possibility that toxins from the organism could enter the food chain through menhaden. There is no evidence so far that the toxins accumulate in the fish, officials say.

Pressure for action to restrict the run-off of nutrients from Maryland's large chicken industry in response to the incidents appears to be waning, however. A plan is already in place to cut these by 40 per cent, and Glendening says he has no plans to legislate further.

Carol Browner, EPA's administrator, who attended the Annapolis meeting, said that the fish kills were “a clarion call” to address the flow of nutrients and other pollution into natural waterways. Not everyone is convinced, however. As Karen Steidinger points out, Spanish explorers of the Florida coast were warned about annual fish kills by the Indians — in 1560.

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KAREN TAM/AP

Toxic shocker: the organisms blamed for fish kills are related to Pfiesteria piscicida (above), whose discoverer, JoAnn Burkholder (below), b. lames it for neurological symptoms she has experienced.