We investigated the effect of food quality on somatic growth and reproduction of zooplankton at different temperatures (12uC, 15uC, 20uC, and 25uC). 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 12uC and 15uC; however, such differences decreased at 20uC and were negligible at 25uC. 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.Since the conceptual work of trophodynamics by Lindeman (1942), determining factors that affect matter transfer efficiency is a key issue in ecology. In aquatic food webs, the efficiency of energy transfer at the plant-animal interface is highly variable (Brett and Mü ller-Navarra 1997), consequently resulting in variable secondary production. Thus far, several studies have been motivated by this variability of dietary energy transfer at the phytoplankton-zooplankton interface, and it has been clear for many years that these variations can be attributed to the variation in food quality of algae for herbivorous zooplankton (Ahlgren et al. 1990; Mü ller-Navarra and

1. Zooplankton are important in transferring dietary nutrients, including polyunsaturated fatty acids (PUFA), up through aquatic food webs. 2. We tested the hypothesis that the taxonomic composition of zooplankton affects the retention and subsequent transfer of PUFA from upwards through the food web. Using laboratory experiments, we investigated dietary PUFA accumulation and bioconversion capacities of six cladoceran species (Ceriodaphnia sp., Daphnia longispina, Daphnia magna, Daphnia pulex, Scapholeberis mucronata and Simocephalus vetulus) fed on two diets (Scenedesmus obliquus and Cryptomonas sp.) that differed in their PUFA profiles. We performed experiments at two different temperatures (14 and 20°C) to assess the role of temperature in the trophic transfer of PUFA. 3. There was little variation in the concentrations of PUFA in these cladocerans which were controlled by dietary PUFA supply. Moreover, as expected, the concentrations of PUFA in all cladoceran species were higher at low temperature. 4. However, even if the composition of PUFA in the cladoceran species generally corresponded to that in their diet, preferential accumulation of some PUFA was recorded in all these taxa. When fed on a highly unsaturated fatty acid-deficient diet, all the cladocerans showed some ability to convert C18-PUFA into arachidonic acid and eicosapentaenoic acid. Interspecific variation in the ability to accumulate and bioconvert PUFA in cladocerans was more pronounced at low temperature (14°C) for both diets. 5. Our results strongly suggest that in heterogeneous habitats with food partitioning between co-existing cladocerans, foraging behaviour may affect the transfer of PUFA more strongly than interspecific variation in accumulating and ⁄ or bioconverting dietary PUFA.