Biokinetics and discrimination factors for δ13C and δ15N in the omnivorous freshwater crustacean, Cherax destructor

Knowledge and understanding of biokinetics and discrimination factors for carbon-13 (delta C-13) and nitrogen-15 (delta N-15) are important when using stable isotopes for food-web studies. Therefore, we performed a controlled laboratory diet-switch experiment to examine diet-tissue and diet-faeces discrimination factors as well as the biokinetics of stable-isotope assimilation in the omnivorous freshwater crustacean, Cherax destructor. The biokinetics of delta C-13 could not be established; however, the delta N-15 value of C. destructor tissue reached equilibrium after 80 +/- 35 days, with an estimated biological half-time for N-15 of 19 +/- 5 days. Metabolic activity contributed to the turnover of N-15 by nearly an order of magnitude more than growth. The diet-tissue discrimination factors at the end of the exposure were estimated as -1.1 +/- 0.5% for delta C-13 and +1.5 +/- 1.0% for delta N-15, indicating that a delta N-15 diet-tissue discrimination factor different from the typically assumed +3.4% may be required for freshwater macroinvertebrates such as C. destructor. The diet-faeces discrimination factor for delta N-15 after 120 days was estimated as +0.9 +/- 0.5%. The present study provides an increased understanding of the biokinetics and discrimination factors for a keystone freshwater macroinvertebrate that will be valuable for future food-web studies in freshwater ecosystems.