We report the effects of small-scale turbulence at realistic intensity (epsilon = 1.1 x 10(-2) cm(2) s(-3)) on the growth and grazing rates of three marine heterotrophic dinoflagellates (Peridiniella danica, Gyrodinium dominans and Oxyrrhis marina) and one ciliate (Mesodinium pulex). All the dinoflagellates showed a reduction of volume-based growth rates, whereas M. pulex did not. P. danica was the most affected by small-scale turbulence, followed by G. dominans, and O. marina. Turbulence slightly increased O. marina ingestion rates, but this increase was not statistically significant. G. dominans and M. pulex ingestion rates were modestly lower under turbulence, and P. danica completely ceased feeding in turbulent treatments. Gross growth efficiencies of G. dominans and O. marina were negatively affected by turbulence, whereas they remained unaltered for M. pulex. P. danica feeding and growth rates in the presence of turbulence were close to zero. Overall, there was a negative relationship between the effects of turbulence on ingestion rates and the time needed to process a prey item. Neglecting the effects of turbulence in microzooplankton grazing estimates in the field could produce biased approximations of their impacts on primary producers.