DEGREE OF TASTE DISCRIMINATION AMONG SUSPENSION-FEEDING CLADOCERANS AND COPEPODS - IMPLICATIONS FOR DETRITIVORY AND HERBIVORY

We used the Rassoulzadegan-DeMott bead bioassay to evaluate the ability of various pelagic microcrustaceans to discriminate between particles on the basis of taste and size. The test examined zooplankton reactions to fresh algal exudates adsorbed onto polystyrene microspheres. The investigation shows that there is a marked dichotomy between certain large-bodied freshwater microcrustaceans in how they respond to small particles; it confirms that large daphnid cladocerans exhibit no taste discrimination for small beads, whereas calanoid copepods continually appraise resource quality of both small and large particles with a fine degree of discrimination. In contrast, smaller bodied daphnids and other cladocerans show some degree of taste and acute size discrimination, the former presumably related to processing large particles one at a time and to the individual peculiarities of the filtering mechanisms. Based on the findings from taste discrimination tests, we suggest that the degree of taste discrimination is often related to particle size. Moreover, we assert that many cladocerans are categorized more appropriately as detritivores than as herbivores, although they exhibit modest, size-related taste discrimination.