MEPS 358:173-179 (2008)  -  DOI: https://doi.org/10.3354/meps07306

ABSTRACT: Juveniles of the Pacific oyster Crassostrea gigas were reared on a monospecific microalgal diet in order to quantify their ¹³C and ¹⁵N diet–tissue fractionations. The weights of these juveniles increased by up to 18-fold within 33 d. The juveniles reached isotopic equilibria with the diet, enabling calculations of fractionation values. The ¹³C fractionation for tissues containing lipids ranked as 0.6‰ (gill lamella) >0.3‰ (adductor muscle) >–0.2‰ (mantle lobe) >–0.9‰ (whole soft body) >–2.2‰ (midgut gland), while the ¹⁵N fractionation ranked as 8.7‰ (adductor muscle) >6.5‰ (mantle lobe) >5.4‰ (whole soft body) >5.2‰ (gill lamella) >2.3‰ (midgut gland). Removal of lipids shifted the diet-equilibrated δ¹³C and δ¹⁵N values in all tissues except the adductor muscle, with resultant increases in the ¹³C and ¹⁵N fractionation values. The expected annual mean δ¹³C value for the diet of the oyster in the field is –17.0‰, which is an intermediate value among the δ¹³C of coastal phytoplankton (–20.2‰), epilithon (–20.0‰), epipelon (–14.8‰), and seaweeds (–14.9‰), suggesting that the oyster feeds on a mixture of these micro- and macroalgae. The expected δ¹⁵N diet value is 3.1‰, which is more depleted than values for micro- and macroalgae, suggesting that the ¹⁵N fractionation in the field is smaller than that obtained from the feeding experiment.

KEY WORDS: Stable isotopes · Trophic enrichment · Bivalve · Feeding experiment · Chaetoceros · Crassostrea gigas