²Kunsan National University, Kunsan, Korea

Preliminary attempts to culture Amoebophrya sp. ex. Gymnodinium sanguineum from Chesapeake Bay indicated that parasite success may be influenced by water quality. To explore that possibility, we determined parasite generation time, reproductive output, and survivorship of progeny (i.e., dinospores) for host-parasite populations grown in high, intermediate, and low nutrient medium. Parasite generation time normalized to host cell volume showed significant differences among treatments, with infections progressing most rapidly in nutrient replete medium. Parasites of hosts grown in nutrient replete medium also produced 3-4 times more dinospores that those infecting host under low nutrient conditions. Furthermore, the percent of dinospores that established new infections was significantly greater for "high-nutrient" vs. "low-nutrient" parasites. In separate experiments, we determined swimming speed and photosynthetic performance of synchronously infected G. sanguineum relative to parasite age. Host swimming speed decreased gradually throughout the infection cycle, showing a 40% total reduction prior to death of the host. By contrast, photosynthesis at saturating irradiance decrease abruptly by about 60% early in the infection cycle and then remained stable through maturation of the parasite. Results indicate that Amoebophrya sp. is well adapted to exploit host populations of enriched coastal environments and exerts significant controls on host behavior and physiology.