Rates of grazing, growth, and respiration were studied in the heterotrophic dinoflagellate Gyrodinium dominans experiencing a single pulse of prey. Additionally, rates of grazing and growth were compared to those of G. dominans growing with constant concentrations of prey. The maximal specific growth rates of G. dominans with a single pulse of prey were similar to those observed when G. dominans was acclimated to constant levels of prey. Thus, our results support the hypothesis that the growth of G. dominans responds quickly to changes in the abundance of prey. Moreover, growth rates were negative when concentrations of prey were low; this would suggest that G. dominans is adapted to eutrophic conditions. Respiration rates were higher than growth rates when G. dominans was fed a single pulse of prey, and we hypothesize that the ability to respond numerically to a changing abundance of prey may inflict high metabolic costs. Gross growth efficiencies (GGEs), determined for G. dominans in both food availability conditions, were within the range of values reported for other heterotrophic protozoans, and while GGE decreased when concentrations of food were high in organisms fed a single pulse of food, the opposite was observed in organisms acclimatized to a constant level of food