Abstract

To provide a basis for a stable carbon and nitrogen isotope ratio (δ 13 C / δ 15 N) analysis to determine the assimilated organic matter in sea cucumber, Holothuria scabra, diet-tissue fractionations were experimentally determined by mono-feeding rearing with diatom. While δ 15 N fractionation of the whole body wall (2.4‰) was similar to the commonly accepted value (2.6 – 4‰), δ 13 C fractionation of the body wall (4.2‰) showed considerable discrepancy with the commonly accepted value (0 – 1‰) due to the high content (35% dry wt/wt) of calcareous spicules (CaCO3) in the body wall, which had significantly higher δ 13 C (-8.6‰) than the organic fractions. Computational elimination of spicules based upon spicule content and spicule δ 13 C reduced the δ 13 C fractionation of the body wall to 1.5‰, close to the common value. δ 13 C fractionation after spicule removal by acid decarbonation and subsequent rinsing (3.2‰) did not agree with the common value, and δ 15 N fractionation was significantly elevated by decarbonation. δ 15 N and δ 13 C fractionations of the intestine (1.5 and 2.2‰, respectively) did not agree with the common values. Since δ 13 C and δ 15 N of the feces did not differ significantly from those of the diet, feces may be used to determine ingested organic matter in the wild.

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