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Hundreds, sometimes thousands of dead fish, their bodies disfigured by bizarre open sores--these were the press reports out of eastern North Carolina in the early Nineties. Baffled scientists tested for the usual fish kill suspects and found none. What was wrong?
The answer came when NC State veterinary scientists filled one of their brackish water aquariums with Pamlico River water and 300 fish promptly went belly up. The water contained no known pollutants, bacteria, or pathogens. But it was swarming with microscopic, animal-like cells of a previously unknown species, now called Pfiesteria piscicida (pronounced feast-er-ia pis-ki-seed-a). Dr. JoAnn Burkholder, an NC State aquatic botanist, has become the best-known authority on pfiesteria and its environmental effects, but many other scientists are studying the organism.
Since this discovery was announced, public concern about pfiesteria has reached a high level, encouraged by television reports and a recent book. Concern is certainly justified, because pfiesteria is potentially a dangerous organism and its abundance in our waters is a troubling symptom of their ill health. But scientific research is finding the answers about pfiesteria, and following this research can help students understand the nature and processes of science.
There are at least four things we'd like scientists to tell us about pfiesteria: (1) What is it and what is it doing in our waters? (2) Is it a menace to public health--to swimmers, boaters, and fisherman? (3) What areas are prone to pfiesteria? and (4) How is the pfiesteria problem related to water quality in North Carolina estuaries? There's considerable progress on all of these questions.
(1) Pfiesteria is a dinoflagellate. Dinoflagellates are neither plants nor animals, although they may sometimes appear like one or the other (pfiesteria is as predatory as any animal, but it can also photosynthesize like a plant after dining on algae). Pfiesteria is a good example for students: a member of the vast zoo of single-celled creatures now considered by biologists to be a separate kingdom (or perhaps several kingdoms) distinct from the familiar plant and animal kingdoms.
Most dinoflagellates are quite harmless. They form a large part of the plankton, the floating collection of small marine organisms which is the bottom of the oceanic food chain. However, some dinoflagellates are toxic, producing powerful nerve poisons dangerous to fish and even to people. Because many of these toxic dinoflagellates are reddish, a large concentration of them is known to fishermen as a "red tide." Red tides are a problem in coastal waters in many parts of the world, but only rarely in North Carolina.
Red tide dinoflagellates produce poisons to deter fish from eating them. Pfiesteria uses its toxins actively to attack and eat fish, behavior which had never been seen before in a dinoflagellate. Pfiesteria is the "T. rex" of the dinoflagellate world.
Scientists are convinced that pfiesteria is not a recent invader. It has always been present in North Carolina waters, and it may play an ecological role in reducing fish populations during times when low oxygen levels and high nutrient levels reduce the water's ability to sustain fish. Furthermore, pfiesteria is not confined to North Carolina waters; it has been found throughout the South Atlantic coastal area, from Delaware to Florida at least. During the summer of 1997 pfiesteria became a serious problem on the Pocomoke River on the Delmarva Peninsula in Maryland. This appearance so close to the nation's capital has raised pfiesteria's profile in the national press considerably.
(2) Pfiesteria is indeed dangerous. Researchers in the NC State lab of Dr. JoAnn Burkholder quickly found that its toxins cause neurological symptoms, including memory loss, disorientation, and speech impediments. One researcher had to be hospitalized before adequate laboratory precautions were worked out.
But does pfiesteria cause illness "in the wild," along the rivers and sounds of eastern North Carolina? This seems like a danger, but it is hard to prove it has actually happened. There is plenty of what scientists call "anecdotal" evidence: individual cases of illness that sound as if they might well be related to pfiesteria. In Maryland, a family of people working on the water reported they suffered "shortness of breath, nausea, leg sores and even memory loss," and a local doctor treated a man who "suffered a severe headache and 30 lesions after waterskiing in the lower Pocomoke for a half-hour." Doctors from the Johns Hopkins and University of Maryland medical schools examined a number of these people and concluded that pfiesteria toxins were the most likely cause of their illnesses.
There have been similar reports of illness in North Carolina, especially among people working in and on the water along the lower Neuse and Pamlico Rivers. North Carolina doctors and scientists are investigating a number of these cases.
Although these reports make it seem likely that pfiesteria can cause illness in humans, a careful study in North Carolina failed to find any proof.
Scientists investigating the possibility decided to study crabbers, because of all folks working or playing on the estuaries crabbers have the greatest amount of actual contact with the water. Scientists studied three groups:
They found that crabbers, compared to ordinary folks, suffer a high rate of various skin problems (such as skin cancers) which are almost certainly associated with their occupation. But crabbers in areas subject to pfiesteria did not suffer any higher rates of these problems than crabbers in pfiesteria-free areas. Both crabbers and non-crabbers had very low rates of neurological problems, the problems caused by pfiesteria in the laboratory. This study is an excellent example of how scientists control variables to reach valid conclusions.
JoAnn Burkholder has written this about pfiesteria and humans:
"It will not be possible to determine the extent to which people in our estuaries are being affected by pfiesteria toxins, or whether it is safe to consume fish from toxic outbreak areas, until we have a way to diagnose the presence of these toxins. That will require identification of the chemical toxins produced by pfiesteria, which is the subject of intensive research."
In late August 1997, North Carolina scientists announced they had identified the toxins and devised a possible test for them; if this test works in nature we may soon know much more about pfiesteria's distribution and effects.
(3) Pfiesteria outbreaks are limited in both time and space. News reports sometimes make it seem that pfiesteria infests all North Carolina waters all the time, but this is far from the case. Pfiesteria outbreaks occur only during the warmer months (June through October) and only in the slow-moving waters of the lower Neuse, Pamlico, and New River estuaries. Pfiesteria never occurs in inland waters, in lakes, or in the ocean, and there have been no outbreaks in the open waters of Pamlico and Albemarle Sounds.
(4) The pfiesteria outbreaks are associated with the known water quality problems in North Carolina estuaries. This seems very clear now. Pfiesteria has become a big problem in waters having low oxygen levels and high nutrient loads caused by sewage discharges and agricultural runoff. But so far we don't know just what factors are most important in triggering pfiesteria outbreaks. It's easy for concerned people to link pfiesteria to their favorite environmental villain (hog farms, golf courses, municipal sewage discharges, septic fields). No doubt all of them are involved in one way or another. But there is no data yet allowing us to apportion blame.
Clearly there is much for us to learn about this denizen of our rivers and estuaries. The pfiesteria story is still in the process of being told. New research, possibly this school year, will add to our understanding. And because of the high level of public concern, it should be easy to follow this process on the Internet.
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Originally posted July 2, 1997; fourth revision, June 5, 1998. Features remain online as long as they remain current. They may be updated if new information becomes available.
Copyright © 1998, Center for Mathematics and Science Education. Teachers have permission to duplicate this page for use in teaching their own classes. All other rights reserved. You are welcome to link to this page, but do not copy its contents.
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