Effect of temperature on an alga‐grazer trophic transfer: A dual stable isotope (13C, 15N) labeling experiment

In this study, we examined the impact of temperature on the carbon and nitrogen trophic transfers from a macroalga to a macro‐grazer by the use of dual ¹³C‐ and ¹⁵N‐labeling. Using an experimental approach in mesocosms, individuals of the urchin Psammechinus miliaris were maintained for 1 month at 17°C (mean summer temperature in the Bay of Brest) and at 20°C (maximum summer temperature) and fed with ¹³C‐ and ¹⁵N‐labeled Solieria chordalis. The results showed that the urchins’ ¹³C uptake was 0.30 µg¹³C g dry weight (DW)^?1 at 17°C and 0.14 µg¹³C g DW^?1 at 20°C at the end of the experiment. The lower uptake at the higher temperature may be attributed to a decrease in metabolic activity at 20°C, involving lower feeding and/or respiration rates. Conversely, no significant effect of temperature was detected on ¹⁵N uptake. At the end of the experiment, the urchins’ ¹⁵N uptake was 0.04 µg¹⁵N g DW^?1 at 17°C and 0.03 µg¹⁵N g DW^?1 at 20°C. This suggests that temperature may affect carbon and nitrogen trophic fluxes differently. The use of dual isotope labeling offers interesting prospects and needs to be further extended in order to better understand trophic interactions in marine communities and the consequences of current environmental changes, such as global warming.