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 monitored over 1 year in a small artificial pond. Grazing rates on fluorescently labelled bacteria were also determined.
• 2 The data showed population dynamics similar to other small freshwater bodies; diatoms were numerous during the spring, chlorophytes dominated during the summer months, and mixotrophs, in particular Gymnodinium, dominated during the autumn and winter.
• 3 The mixotrophic dinoflagellates were responsible for a high chlorophyll concentration during the autumn and winter. Mixotrophs were important consumers of bacteria, particularly during the autumn when population densities of pure heterotrophs were low. Mixotrophs were an important component of the microbial food web in this pond.