Determination of δ13C and δ15N and trophic fractionation in jellyfish: implications for food web ecology
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Application of stable isotope analysis (SIA) in jellyfish allows definition of trophic patterns not detectable using gut content analysis alone, but analytical protocols require standardization to avoid bias in interpreting isotopic data. We determined δ13C and δ15N in Aurelia sp. from the northern Gulf of Mexico (30°00′N, 89°00′W–30°24′N, 88°00′W) to define differences in stable isotope composition between body parts and whole body, the effect of lipid extraction on δ13C in tissues, and fractionation values from medusa to prey. The isotopic composition of bell and whole Aurelia sp. was not different. The increase in δ13C values after lipid removal suggested a correction is needed. To aid future analyses, we derived a correction equation from empirical data for jellyfish samples. Laboratory feeding experiments indicated medusae increased +4 ‰ in δ13C and +0.1 ‰ in δ15N compared to their diet. These results suggest protocols commonly applied for other species may be inaccurate to define Aurelia sp. trophic ecology. Because Aurelia spp. are commonly found in marine ecosystems, accurately defining their trophic role by use of SIA has implications for understanding marine food webs worldwide.
Funding for this study was provided by the National Oceanographic and Atmospheric Agency (NOAA)–R.C. Shelby Center for Ecosystem-Based Fisheries Management and National Science Foundation NSF-RAPID (OCE-1043413) to WMG. We thank the Biological Oceanography and Fisheries and Oceanography of Coastal Alabama (FOCAL) laboratories and Technical Support at the Dauphin Island Sea Lab for sample collection and maintenance of living animals. We are particularly grateful to R. Collini, C. Culpepper, J. Herrmann, L. Linn, S. Muffelman, R. Shiplett, and K. Weiss for their invaluable help. D. Harris and J. Matthews at the SIF at UC Davis and C. Cook and B. Errkila at SIRFER provided suggestions for sample analysis. L. Carassou, F. Hernandez Jr, A. Hunter, A. Malej, and two anonymous reviewers improved earlier drafts of the manuscript.
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