The role of mixotrophic protists in the population dynamics of the microbial food web in a small artificial pond

1. The seasonal variations of protist and rotifer populations were monitore d over 1 year in a small artificial pond. Grazing rates on fluorescently la belled bacteria were also determined. 2. The data showed population dynamics similar to other small freshwater bo dies; diatoms were numerous during the spring, chlorophytes dominated durin g the summer months, and mixotrophs, in particular Gymnodinium, dominated d uring the autumn and winter. 3. The mixotrophic dinoflagellates were responsible for a high chlorophyll concentration during the autumn and winter. Mixotrophs were important consu mers of bacteria, particularly during the autumn when population densities of pure heterotrophs were low. Mixotrophs were an important component of th e microbial food web in this pond.