TEACHING ALL VOLUMES SUBMIT WORK SEARCH TIEE
VOLUME 1: Table of Contents TEACHING ISSUES AND EXPERIMENTS IN ECOLOGY
Issues : Figure Sets

Figure Set 4: What is the ecology and biology of Pfiesteria?

Purpose: Help students better understand the ecotoxicological effects of nitrogen loading to estuaries.
Teaching Approach: "jigsaw"
Cognitive Skills: (see Bloom's Taxonomy) — comprehension, interpretation, application, evaluation
Student Assessment: newspaper article

BACKGROUND


The Pfiesteria story is fascinating from many points of view - ecological, political, personal. Its life history is so bizarre that students think you are telling them a science fiction story. The politics center around JoAnn Burkholder, a microbial ecologist from North Carolina State University, who is either admired or chided, depending on who you are talking to. The politics are those related to the chicken and hog industry in North Carolina. Federal politics also come into play because funding for Pfiesteria research was limited until the dinoflagellate was linked to fish kills in the Chesapeake Bay (Washington D.C. is of course very close to the Bay).

Burkholder's first paper on Pfiesteria piscicida was published in Nature in 1992. Since then researchers have learned a great deal about its highly complex life cycle (more than 20 different stages), its mode of attack on fish and other animals, the action and structure of the Pfiesteria toxin, factors that stimulate the toxic forms to grow in nature, and its presence in other estuaries in the U.S. and globally. There are many websites about Pfiesteria and numerous references are listed below. BioScience devoted a whole issue (vol. 51, no. 10; 2001; Magnien 2001, Grattan et al. 2001, Staver and Brinsfield 2001) to Pfiesteria outbreaks - the history, the policy, human health risks, and agricultural contamination of receiving waters. See also numerous www sites in the resource section.

Pfiesteria piscicida was discovered by accident when a colleague of Burkholder noticed that the fish tilapia held in tanks suddenly died several days after being exposed to water collected in the Pamlico River, NC. The scientists observed that density of a small dinoflagellate increased before fish death and declined rapidly in number unless live fish were introduced. The dinoflagellate produced resting cysts or non-toxic amoeboid forms in the absence of fish (Burkholder et al. 1992). When Burkholder and her colleagues looked for dinoflagellates during massive fish kills in local estuaries Pfiesteria was abundant, but only when fish were dying. In the Nature paper they name Pfiesteria as the causative agent of the many unexplained fish kills in NC estuaries, they identify a neurotoxin from the dinoflagellate as the lethal agent, and they link fish kill events to nutrient enriched Pfiesteria blooms (Burkholder et al. 1992).

In subsequent studies, Burkholder reported that toxic forms of Pfiesteria were stimulated by inorganic and organic phosphate (e.g. Burkholder and Glasgow 1997). She became embroiled in arguments with NC officials about the role of the state's hog farm effluents in stimulating Pfiesteria growth. Nitrogen entered the story in the late 1990's when the incredible nutritional versatility of the dinoflagellate became clearer. In addition to consuming dissolved organic compounds (such as in animal waste), Pfiesteria retains chloroplasts from algae that it consumes when fish are not available. Pfiesteria zoospores with these inclusions, called kleptochloroplasts, are stimulated by N and P. In addition to stimulating the growth of Pfiesteria zoospores directly, N indirectly contributes to growth of the dinoflagellate because N is a limiting nutrient for phytoplankton in estuaries. Therefore, N loadings stimulate phytoplankton growth which in turn contribute to proliferation of Pfiesteria.

The neurotoxin excreted by Pfiesteria deserves special mention. Until the discovery of Pfiesteria, estuarine ecologists often had a difficult time explaining to legislators and the public how too many nutrients, which sound like good things, could be bad. In addition to the vocabulary problem, nutrient loading does not directly give people diseases or make them sick. For both these reasons, explaining that nutrient loading to estuaries is a severe environmental problem has been an uphill battle.

But Pfiesteria does make people sick. Both Burkholder and Howard Glascow, who works with her, suffered serious neurological effects when they unknowingly inhaled the Pfiesteria toxin. The scientists were hospitalized and affected for months.

Pfiesteria is the first reported dinoflagellate that produces aerosols that seriously harm human nervous systems. Symptoms include acute respiratory problems blurred vision, nausea, vomiting, extreme headaches, and severe memory dysfunction. According to Burkholder and Glasgow (2001) "For days to weeks following exposure, several laboratory personnel could recognize words individually but could not form sentences, perform simple arithmetic, or remember more than the last words of a sentence directed to them. The most seriously affected person in our laboratory, who is a highly intelligent researcher, managed only a 7-year-old's reading level for 3 months after exposure and required reading lessons at first to help regain reading ability … two others … could not remember their names or where they had lived." One of the many controversial aspects of the Pfiesteria story is the degree to which fishermen were harmed by neurotoxin aerosols during Pfiesteria blooms.

A note about the book And The Water Turned To Blood by Rodney Barker (see resources below for websites): this is a fascinating read, written like a biological thriller. Barker is far from neutral in the book; he sides with Burkholder and sensationalizes the story. My students loved the book and were quite conscious of the sensational journalism; discussion of the book could stimulate a lively discussion about objectivity in science and journalists as science reporters.

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Literature Cited

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