Estuarine and oceanic microflagellate predation of actively growing bacteria: estimation by frequency of dividing-divided bacteria

Rates of predation and clearance of heterotrophic microflagellates, isolated from estuarine and oceanic environments, were estimated using actively growing bacterial prey. In separate experiments, a significant relation (by linear regression) was found between bacterial growth rate and frequency of dividing-divided cells (FDDC) for a species of Vibrio. This relation allowed the estimation of flagellate predation rates on these bacteria by comparing net bacterial growth with expected growth, predicted by FDDC, relative to the enumerated flagellate populations. Cell measurements and counts also allowed the estimation of flagellate clearance rates. Results suggest that flagellates can effectively prey upon bacteria at environmental concentrations ranging from 10⁵ to 10⁷ bacteria ml⁻¹ at average rates ranging from 30 to over 200 bacteria flagellate⁻¹ h⁻¹. Environmental concentrations of flagellates further suggest that they play a dominant role as bacterial grazers in marine plankton.