MEPS 462:175-190 (2012)  -  DOI: https://doi.org/10.3354/meps09786

ABSTRACT: Consumer-diet discrimination factors (Δ¹⁵N and Δ¹³C) are often applied without corroboration from laboratory experiments. Deviations in Δ¹⁵N and Δ¹³C that may occur from different diet types were quantified by raising 120 sea urchins Lytechinus variegatus in laboratory tanks on 3 different diets: seagrass Thalassia testudinum, red foliose macroalgae (Grauteloupia sp. and Palmaria palmata) and a mixed diet specifically formulated for L. variegatus. Patterns of δ¹³C and δ¹⁵N and resulting fractionation factors were then determined in muscle, gonad, gut, test organic matrix and whole individuals. Tissue δ¹³C values showed a strong positive association with δ¹³C of diets and estimates of absorption efficiency (R² = 0.81). The seagrass diet consistently resulted in negative Δ¹³C values in all tissues (from −0.86‰ in muscle to −1.63‰ in gonad) and whole individuals (−1.19‰), whereas macroalgal and formulated diets showed positive values (0.11 and 0.19‰, respectively). Only individuals on the formulated diet clearly reached isotopic equilibrium for δ¹³C, suggesting that other lower quality diets may have resulted in more continuous reallocation of internal resources. δ¹⁵N values increased as the nitrogen content of these diets decreased (3.18, 1.21 and 0.82‰ for seagrass, macroalgae and formulated diets, respectively). Overall differences in the biochemical composition of diets and a robust relationship between δ¹³C and δ¹⁵N signatures suggest that protein quantity and quality could be central in driving isotope fractionation. The influence of macrophyte material type in the diet can be stronger than that of trophic level for both δ¹³C and δ¹⁵N, so further compound-specific isotope analyses are necessary to determine reliable values of Δ¹³C and Δ¹⁵N for ecological applications.

KEY WORDS: Seagrass · Macroalgae · Omnivory · Diet quality · Absorption efficiency

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Cite this article as: Prado P, Carmichael RH, Watts SA, Cebrian J, Heck KL Jr (2012) Diet-dependent δ13C and δ15N fractionation among sea urchin Lytechinus variegatus tissues: implications for food web models. Mar Ecol Prog Ser 462:175-190. https://doi.org/10.3354/meps09786 Export citation Share:    Facebook - - linkedIn