FEEDING AND ENERGY RELATIONS IN DAPHNIA-GALEATA-MENDOTAE

We have compared the energetic cost to Daphnia galeata mendotae of fee ding on Scenedesmus quadricauda, a green alga, Asterionella formosa, a diatom. and Anabaena sp., a filamentous blue-green cyanobacterium bot h singly and in combination. The ecological implications of the result s are discussed in terms of ecosystems where blue-green algal blooms a re common. The filtering and assimilation rates were measured using st andard C-14 algal labeling techniques, and respiration rates were dete rmined with the ENDECO and Strathkelvin dissolved oxygen systems. Feed ing behavior of D. galeata mendotae was observed and quantified by ana lyzing videotaped feeding behavior. Increased rejection rates, lower f iltering and assimilation rates, and higher respiration per unit of fo od eaten associated with feeding on combinations of algae containing A nabaena sp. filaments relative to combinations where Anabaena sp. is absent supports the hypothesis that large cladocerans such as D. galea ta mendotae are poor competitors in environments where cyanobacterial blooms are common.