Stoecker 9317732 This study will examine the feeding ecology of two red-tide dinoflagellates Gymnodinium sanguineum and Ceratium furca. Laboratory and field studies will test the hypotheses that mixotrophic dinoflagellates: (1) are primarily photosynthetic organisms that become phagothrophic when nutrient and/or light environments are suboptimal; (2) exploit a variety of nano- and microplankton prey, but can exhibit feeding preferences; (3) gain sufficient nutritional benefits through phagotrophy to promote enhanced photosynthesis and growth; and (4) feed on a diel cycle with elevated ingestion of prey during the day. Mixotrophic dinoflagellates appear to have relatively slow feeding rates, but their sheer numbers under bloom conditions indicate their potential importance to microbial food-web structure and function. Without a greater understanding of feeding behavior in mixotrophic dinoflagellates, their significance to microbial food web dynamics and red-tide ecology will remain speculation. ***
