Pfiesteria piscicida

The proliferation of harmful algal blooms (HABs) is increasingly becoming a world-wide problem. Over the past 2 decades, HABs have not only increased in frequency and areal extent, but have caused considerable economic loss and public health problems (Boesch et al. 1997; Burkholder and Glasgow, 1997; Horner et al. 1997; Smayda 1997). The Pfiesteria outbreak in 1997 in Maryland alone has been estimated at over $3 million dollars (MD Dept. of Agric. Statistics). Links between HAB's and nutrient loading have often been made (e.g. Reigman 1990; Smetecek et al. 1991; Paerl 1993; Burkholder et al. 1997). Specifically, nutrient enrichment has been shown to stimulate Pfiesteria and related species (Burkholder and Glasgow 1997). Inorganic phosphate has been shown to stimulate both recently toxic zoospores and nontoxic zoospores of Pfiesteria (Burkholder et al. 1997), and direct uptake of nitrogenous nutrients has also been demonstrated for Pfiesteria (Lewitus et al. 1999). Organic nitrogen has also been shown to be highly correlated with the development of Pfiesteria and other harmful dinoflagellates (Gilbert and Terlizzi, subm). Furthermore, nutritional history is considered to be important in controlling Pfiesteria's response to nutrient enrichment (Burkholder and Glasgow 1997). In cultures, production of long-term nontoxic zoospores that previously had been given nutrient-poor algal prey was stimulated by phosphate and nitrate enrichments, whereas negligible increases in cell density occurred under nutrient enrichment of nontoxic Pfiesteria that previously had been fed nutrient-rich prey (Burkholder et al. 1997). With a life cycle of unprecedented complexity, and equally complex nutritional responses, the environmental factors promoting the growth of Pfiesteria have been difficult to unravel. However, such relationships are critical to establish because of the environmental, economic, and political consequences of blooms of this organism.

Pfiesteria has been classified as a "heterotrophic" dinoflagellate due to its inability to produce chloroplasts de novo, yet has the ability to function as an algal cell when it acquires chloroplast from other cells. Positive, linear correlations for non=toxic Pfiesteria zoospores and sample chlorophyll concentrations have been noted for North Carolina estuaries (Fensin 1998), and high algal productivity seems to have been associated with other Pfiesteria and Pfiesteria-like events have been observed (Paerl and Pickney 1998; MD DNR Report 1997).

Pfiesteria has been implicated as the primary causative agent of many fish kills along the south-eastern seabord, especially Nroth Carolina and Chesapeake Bay. Pfiesteria only become toxic when it detects fish secreta/excreta. The amoeboid stages of Pfeistera feed preferentially on bits of fish tissue, while some of the other life stages feed preferentially on algal prey. Organic matter and algae also form a large part of the diet of juvenile menhaden (Lewis and Peters 1994). High juvenile menhaden densities are often noted near chlorophyll maxima in estuaries (Friedland et al. 1996). Thus, high chlorophyll levels co-occur with both Pfiesteria and Pfiesteria-like organisms as well as juvenile menhaden.

Dinoflagellates in general, and Pfiesteria in particular, prefer low turbulence environments (White 1997; Thomas and Gibson 1990). Conditions at the time of 1997 Maryland fish kills included warm midsummer temperatures, calm conditions and hypoxia in shallow waters of moderate salinity (MD DNR 1998). These conditions were not only ideal for the growth and persistence of Pfiesteria, but were also ideal for other plankton blooms that attracted fish. Similar conditions have been shown to have co-occur with Pfiesteria outbreaks in N. C. (Burkholder et al. 1995).

The aim of this program is to implement an intensive monitoring program of the environmental conditions leading to Pfiesteria outbreaks. We will monitor environmental parameters, such as chlorophyll, zooplankton, salinity, temperature, as well as physical parameters, such as turbulence, flow and meteorological conditions, nutritional conditions, both inorganic and organic, and the presence or absence of fish. In developing this monitoring program, new techniques will be evaluated with the aim of recommending protocols that cam be adopted in other regional studies.