Estimation of carbon and nitrogen stable isotope fractionation and isotopic turnover in Japanese abalone (<i>Haliotis discus discus</i>) through a diet switching experiment

A diet switching experiment was conducted to clarify the trophic discrimination factors (TDF) for nitrogen and carbon stable isotope ratios in Japanese abalone Haliotis discus discus. The experiment was carried out in complete darkness to prevent contamination by microalgae growth. After the experiment, the weight of the abalone increased three-fold. Nitrogen and carbon stable isotope ratios in the control group showed little change, while the treatment group showed large changes in both values. As a result of this study, the turnover (half-life) for both δ13C and δ15N were estimated to be 1.8. The results indicate that a 1.8-fold increase in the soft body of Japanese abalone results in a half-replacement of the stable isotope ratio. Therefore, the stable isotope ratios of Japanese abalone in natural environment may reflect a more recent diet in young abalone, whereas in older abalone they may represent a long-term average of a diet of more than one year. And TDF for δ13C and δ15N were estimated to be 2.97‰ and 1.13‰, respectively. Although our results for the TDF of Japanese abalone differed significantly from empirical principles, they were in broad agreement with previously reported TDF values for abalone species. Then, application of the results of this study may contribute to an accurate understanding of the feeding habits of Japanese abalone.