Combined effects of food quality and temperature on somatic growth and reproduction of two freshwater cladocerans

We investigated the effect of food quality on somatic growth and reproduction of zooplankton at different temperatures (12 degrees C, 15 degrees C, 20 degrees C, and 25 degrees C). Standardized growth experiments of two cladocerans, Daphnia magna and Simocephalus vetulus, were performed on (1) high-quality food (Cryptomonas sp.), (2) relatively low-quality food (Scenedesmus obliquus), and (3) intermediate-quality food (Cryptomonas : Scenedesmus mixture). Food quality constraints on somatic growth and reproduction of the two cladocerans decreased with increasing temperature. For D. magna and for S. vetulus, differences between clutch size and growth rate of individuals fed on the three food sources were highly pronounced when they were reared at 12 degrees C and 15 degrees C; however, such differences decreased at 20 degrees C and were negligible at 25 degrees C. Variations in food quality constraints with temperature can be explained by the variability of dietary polyunsaturated fatty acids, such as eicosapentaenoic acid and stearidonic acid requirements of these cladocerans. We conclude that dietary constraints exerted by food quality for zooplankton development vary as a function of different temperature conditions.