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1. The distribution of fatty acids in different groups of bacteria, ciliated protozoans and microalgae is reviewed emphasizing specific fatty acids like odd‐branched fatty acids and (n‐3) polyunsaturated fatty acids. 2. Odd‐branched fatty acids and (n‐6) fatty acids appear to be good indicators of zooplankton grazing on bacteria and ciliates when they are detected in microcrustacean triacylglycerols. We give several examples where these fatty acids may be used as markers. The value of (n‐3) fatty acids in describing zooplankton grazing on phytoplankton seems to be low.

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