Researchers are continuing to focus on the nutritional ecology of Pfiesteria, and have established through field and laboratory research that it can be highly stimulated by both inorganic and organic N and P enrichment. The stimulation can occur either directly or indirectly (mediated, for example, by the abundance of algal prey that Pfiesteria consumes when fish are not available). The degree of stimulation depends on (i) the season, and (ii) Pfiesteria‘s nutritional prehistory (i.e., whether food is abundant or scarce, as well as the type of food – for example, when fish are abundant, water-column nutrient supplies are not very important; during spring as Pfiesteria is coming out of a low-activity winter period, it feeds preferentially on certain N-stimulated algal species that can be abundant bloom formers.
In other nutritional research, we are working to identify the substances in fish secreta/excreta that stimulate Pfiesteria to become toxic. And, we are examining interactions between organic and inorganic sources of nitrogen, phosphorus, and carbon in providing nutrition for Pfiesteria. This work involves both laboratory and field experiments. We have also documented stimulation of Pfiesteria by human sewage and swine effluent spills. We are continuing to characterize the effects of these human-derived nutrient sources on production and toxic activity of this dinoflagellate.
In ongoing efforts we are developing a pictorial atlas of Pfiesteria to capture the many morphs (shapes and sizes) of amoeboid, flagellated, and encysted stages. This atlas will be developed using light microscope photographs in conjunction with scanning electron microscope pictures, and it will enable a “presumptive” identification and count of Pfiesteria-like dinoflagellates. Recent discovery of other Pfiesteria-like dinoflagellates (by Drs. K. Steidinger and J. Landsberg and coworkers at the Florida Marine Research Institute) increases the importance of confirmation of toxic activity using laboratory bioassays in specially designed biohazard facilities. We are performing these bioassays on North Carolina field and aquaculture samples, and also on samples from mid-Atlantic and southeastern U.S. states when requested by state agencies or by fishermen and other concerned citizens. Unfortunately, these efforts are very labor-intensive and expensive, so are restricted by space and funding constraints.
Our research with other colleagues (e.g, Drs. S. Shumway, R. Smolowitz) also emphasizes the impacts of toxic Pfiesteria on fish reproduction, recruitment, and disease resistance – that is, impacts of Pfiesteria on commercially important finfish and shellfish species at the population level, well beyond the impacts of a fish kill event. We are working with colleagues at NIEHS, the University of Oklahoma, NMFS-Charleston, and the University of Florida to chemically characterize components of the toxins produced by Pfiesteria, and assess the impacts of these toxins on small mammals in experimental research. Finally, our colleagues at UNC-Greensboro (Dr. P. Rublee) have been developing a DNA probe for Pfiesteria piscicida , which has been tested successfully on water samples from field fish kills. We are hopeful that this probe will be available for widescale use shortly, since it will greatly facilitate identification of P. piscicida from closely related dinoflagellates.