CS16 Harmful Algal Blooms
Date: Wednesday, June 12, 2002
Time: 4:45:00 PM
Location: Sidney
 
LurlingM, Wageningen University, Wageningen, Netherlands, miquel.lurling@aqec.wkao.wau.nl
Van der Grinten, E, , University of Amsterdam, Amsterdam, Netherlands, Grinten@bio.uva.nl
 
DAPHNIA GROWTH INHIBITION IN PRESENCE OF NONTOXIC AND TOXIC MICROCYSTIS
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A non-toxic and toxic strain of Microcystis aeruginosa was offered to Daphnia in mixtures with a good green algal food (Scenedesmus obliquus) to avoid nutritional deficiency. Toxic cells caused a dramatic reduction in growth and resulted in death of the animals, but the addition of purified toxin (microcystin-LR) had no effect on Daphnia. In contrast with the nutritional inadequacy hypothesis, growth on a mixture of Scenedesmus and the nontoxic food was significantly reduced. This observation could not be explained from morphological characteristics of the strain, but was most probably caused by feeding deterrents released from or associated with the Microcystis cells. Based on the results of a short-term feeding experiment, an additional life history experiment with different amounts of Scenedesmus was performed. The results could not reject the hypothesis that feeding deterrence was the causal factor in explaining reduced growth on the food mixture with non-toxic Microcystis. These feeding deterrents should be considered in explaining the food quality of Microcystis and other cyanobacteria as they could affect the total food intake and consequently Daphnia growth.