Impact of turbulence and turbidity on the grazing rate of the rotifer Brachionus calyciflorus (Pallas)

The impact of turbulence and turbidity on Brachionus calyciflorus grazing r ate was determined in short feeding periods (10 min), using labelled Chlore lla pyrenoidosa. The response to water motion of B. calyciflorus depends on it physiological state: the grazing rate of recently fed amictic females s tomach green (with one or two eggs) is significantly reduced in agitated en vironments compared with non-agitated environments. In contrast, the grazin g rate of starved amictic females is not reduced by water motion, whatever its velocity ( V-1=0.18 m s(-1) and V-2=0.22 m s(-1)). In the presence of s uspended particles (3-6-mu m silica beads), a larger reduction in grazing r ate is observed in agitated water at any water velocity (V-1=0.18 m s(-1) o r V-2=0.22 m s(-1)), than in stagnant water. A synergy between turbulence a nd turbidity is unfavourable to feeding of rotifers.