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 (δ13C) and nitrogen-15 (δ¹⁵N) are important when using stable isotopes for food-web studies. Therefore, we performed a controlled laboratory diet-switch experiment to examine diettissue and dietfaeces discrimination factors as well as the biokinetics of stable-isotope assimilation in the omnivorous freshwater crustacean, Cherax destructor. The biokinetics of δ13C could not be established; however, the δ¹⁵N value of C. destructor tissue reached equilibrium after 80±35 days, with an estimated biological half-time for ¹⁵N of 195 days. Metabolic activity contributed to the turnover of δ ¹⁵N by nearly an order of magnitude more than growth. The diettissue discrimination factors at the end of the exposure were estimated as 1.1±0.5% for δ13C and +1.51.0% for δ¹⁵N, indicating that a δ¹⁵N diettissue discrimination factor different from the typically assumed +3.4% may be required for freshwater macroinvertebrates such as C. destructor. The dietfaeces discrimination factor for δ¹⁵N after 120 days was estimated as +0.90.5%. 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.