A preliminary study on enrichment of stable isotope from diets by mud crab (Scylla paramamosain)

Stable isotope analysis technology has become an important means in the study of nutrition sources in ecology, but the premise is to obtain the data of stable isotope enrichment effect of animals in different diets. In this experiment, Acentrogobius caninus, Callionymus richardsoni, Metapenaeopsis barbata, Ruditapes philippinarum, Perinereis nuntia and cultured P. aibuhitensis were collected from mangroves and adjacent beaches and used as baits to feed Scylla paramamosain for 66 d. The results indicate that R. philippinarum, P. aibuhitensis and M. barbata had better culture effects on S. paramamosain. The stable isotope abundances of δ¹³C and δ¹⁵N in the six natural diets were obviously higher than that in initial crabs. Compared with the initial crabs, the contents of stable isotope δ¹³C and δ¹⁵N of final crabs increased significantly. The enrichment effects of the ¹³C (∆¹³C) were 0.7, −0.19, 0.22, 2.58, −0.12 and 2.75 for the six diets, respectively, while the ∆¹⁵N varied from −2.98 to 0.21. Most of these values were inconsistent with the judgment baselines (discrimination) of direct predator and prey, which were 0‰−1‰ for ∆¹³C and 3‰−4‰ for ∆¹⁵N, respectively. This may be due to the huge difference of stable isotope enrichment between beach dwelling organisms and land organisms. It is also possible that low water temperature, slow growth and low weight gain rate of S. paramamosain at later stage of the experiment lead to insufficient renewal of carbon and nitrogen in the body.