Diet-tissue Stable Isotopic Fractionation of Tropical Sea Cucumber, Holothuria scabra

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