Isotopic turnover rate and fractionation in multiple tissues of red rock lobster (Jasus edwardsii) and blue cod (Parapercis colias): Consequences for ecological studies

This study experimentally determined the turnover rates of δ13C and δ15N as a function of growth and metabolism and isotopic fractionation for different tissues in captive populations of red rock lobster (Jasus edwardsii) and blue cod (Parapercis colias). Isotopic turnover was estimated using the model of Hesslein et al. [Hesslein, R., Hallard, K., Ramlal, P., 1993. Replacement of sulfur, carbon, and nitrogen in tissue of growing broad whitefish (Coregonus nasus) in response to a change in diet traced by δ34S, δ13C, and δ15N. Can. J. Fish. Aquat. Sci. 50, 2071–2076.]. Isotopic fractionations relative to diet differed among tissues and isotopes. Lobster muscle was more enriched than hemolymph and blue cod fin tissue was more enriched than blood for δ13C and δ15N. The metabolic component of turnover accounted for > 90% of the total isotopic turnover in lobster tissues and 30%–60% in blue cod tissues. Lobster muscle (half-life 147 d) and hemolymph (half-life 117 d) turnover rates were not significantly different but were faster than turnover rates of blue cod tissues. Whole blood, blood plasma fraction, and the blood cellular fraction had similar turnover rates; the whole blood half-life was 240 d for blue cod. Measuring turnover in larger, slower growing animals allowed for a more precise estimate of the metabolic component of isotopic turnover than in fast growing animals in which change is predominantly the result of dilution through growth. The differences in fractionation values among tissues observed here demonstrate that using generic trophic fractionation values would introduce error into diet reconstruction or migration studies. We demonstrate that a modified version of Hesslein et al.'s [Hesslein, R., Hallard, K., Ramlal, P., 1993. Replacement of sulfur, carbon, and nitrogen in tissue of growing broad whitefish (Coregonus nasus) in response to a change in diet traced by δ34S, δ13C, and δ15N. Can. J. Fish. Aquat. Sci. 50, 2071–2076.] turnover model could be used to estimate the temporal component of migration.