BURKHOLDER 9403920 The diverse heterotrophic dinoflagellates include free- living estuarine species that demonstrate "ambush predator" behavior toward algal, protozoan, or fish prey. This behavioral pattern is widespread; thus far, it has been reported from the Mediterranean Sea, the Gulf of Mexico, and the western Atlantic. Within the past two years, a new genus of ambush predator dinoflagellate, Pfiesteria (nov. gen.) has been discovered, with known species having a complex life cycle that includes at least 15 stages. Among these stages are persistent amoeboid heterotrophs and ephemeral "phantom-like" flagellates that are common in eutrophic mid-Atlantic and Gulf Coast estuaries, and likely are widespread throughout warm temperate and subtropical waters. The ubiquitous occurrence and abundance of these stages in the water column and sediments, their voracious phagotrophy on bacterial, algal, and microfaunal prey, and their lethality to fish point to a major role of ambush predator dinoflagellates in the structure and function of estuarine food webs. This project is to experimentally examine the nutritional ecology and trophic interactions of abundant stages of Pfiesteria piscimorte (nov. gen. et sp.) as a representative toxic ambush predator, toward determining the role of these organisms -- in their many forms -- within estuarine food webs. This project will: (1) examine saprotrophic nutrition of the biflagellate and amoeboid forms on stimulatory secretions of finfish prey; (2) characterize phagotrophic interactions between Pfiesteria (nov. gen.) and bacterial, algal and microfaunal prey; and (3) determine the influence of the biflagellate and amoeboid stages on representative microbial predators. The insights gained from this research will alter general paradigms about the role of dinoflagellates in the structure and function of food webs n eutrophic warm temperate estuaries.
