Effects of temperature on food isotopic integrity and trophic fractionation in Chironomus riparius in laboratory experiments

Our experimental study was designed to assess the effects of temperature on food isotopic integrity and trophic fractionations (of carbon and nitrogen stable isotopes: Δ 13 C and Δ 15 N) in chironomid larvae. A laboratory experiment was run using Chironomus riparius larvae at 15, 18 and 23°C, and under three pulverized food resources. There were significant changes in the stable isotopic composition of the uneaten food, revealing the difficulty of preventing food microbial degradation in rearing experiments. C/N ratios of chironomid larvae were also affected by temperature, regardless of the food resource, suggesting changes in lipid contents and associated effects on the larval δ 13 C values. Therefore, differences in calculation methods (with vs. without lipid normalizations, fresh vs. old food isotopic baselines) induced large variability in Δ 13 C and Δ 15 N values, but our trophic fractionation estimates were similar to those previously reported in literature. Therefore, we conclude that temperature is not a major driver of the variability in trophic fractionations for chironomid larvae, and stable isotope composition of aquatic consumers can be used in food webs studies under changing temperature conditions. Variability in trophic fractionation estimates should, however, be considered to avoid misinterpretations of food web structure.