RATES OF BENTHIC PROTOZOAN GRAZING ON FREE AND ATTACHED SEDIMENT BACTERIA MEASURED WITH FLUORESCENTLY STAINED SEDIMENT

In order to determine the importance of benthic protozoa as consumers of bacteria, grazing rates have been measured by using monodispersed f luorescently labeled bacteria (FLB). However, high percentages of nong razing benthic protists are reported in the literature. These are rela ted to serious problems of the monodispersed FLB method. We describe a new method using 5-(4,6-dichlorotriazin-2-yl)-aminofluorescein (DTAF) -stained sediment to measure in situ bacterivory by benthic protists. This method is compared with the monodispersed FLB technique. Our esti mates of benthic bacterivory range from 61 to 73 bacteria protist(-1) h(-1) and are about twofold higher than the results of the monodispers ed FLB method. The number of nongrazing protists after incubation for 15 min with DTAF-stained sediment is in agreement with theoretical exp ectation. We also tested the relative affinity for FLB of protists and discuss the results with respect to a grazing model.