INTERACTIONS OF A TOXIC ESTUARINE DINOFLAGELLATE WITH MICROBIAL PREDATORS AND PREY

The toxic ambush-predator dinoflagellate, Pfiesteria piscicida (gen. et. sp. nov.) targets finfish and shellfish prey, and is a causative agent of major fish kills in representative estuaries of the southeastern United States. Live fish or their fresh tissues stimulate toxicity and gamete production and fusion, which usually occurs within a benthic or floating gelatinous mass. After fish death, remaining gametes revert to asexual, nontoxic zoospores that thrive in nutrient-enriched waters with flagellated algal prey. in the absence of fish, transformations among nontoxic flagellated, amoeboid and encysted stages in the dinoflagellate's complex life cycle are influenced by the availability of microbial prey (bacteria, algae, and microfauna including protozoan ciliates and rotifers). Three potential microbial predators of P. piscicida were identified, although one was subject to attack especially by larger amoeboid stages. The ubiquitous occurrence of flagellated and amoeboid stages in the water column and sediments of warm temperate/subtropical waters, and their voracious phagotrophy on bacterial, algal and microfaunal prey, point to a major role of toxic ambush-predator dinoflagellates in the structure and function of estuarine microbial food webs.