USE OF FLUORESCENTLY LABELED ALGAE TO MEASURE THE CLEARANCE RATE OF THE ROTIFER KERATELLA-COCHLEARIS

1. Fluorescently labelled algae (FLA) were used to measure clearance r ates of the rotifer Keratella cochlearis. The freshwater algae Chlorel la vulgaris and Stichococcus bacillaris were labelled with a fluoresce nt dye, 5-(4,6-dichlorotriazin-2-yl) aminofluorescein (DTAF), followin g a modified staining procedure.2. Keratella cochlearis ingested both algal species. Clearance rates on tracer foods varied between 2.4 and 6.9 mu l ind(-1) h(-1), which are comparable with those determined usi ng other techniques. 3. The main drawback of the FLA technique was tha t only a little more than one-third of the total amount of algal cells of both C. vulgaris and S, bacillaris were well stained with the dye (DTAF), despite the use of a higher concentration of dye and a longer staining period than recommended in the literature. 4. The FLA method can be successfully applied in grazing studies involving size selectio n and competition for food among zooplankton. The method complements e xisting techniques for measuring the clearance and ingestion rates of filter-feeders.