Data from: Amino acid δ15N underestimation of cetacean trophic positions highlights poor understanding of isotopic fractionation in higher marine consumers

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1. Compound specific stable isotope analysis (CSIA) of amino acids (AAs) has been rapidly incorporated in ecological studies to resolve consumer trophic position (TP). Differential ¹⁵N fractionation of ‘trophic’ AAs, which undergo ¹⁵N enrichment with each trophic step, and ‘source’ AAs, which undergo minimal trophic ¹⁵N enrichment and serve as a proxy for primary producer δ¹⁵N values, allows for internal calibration of TP. Recent studies, however, have shown the difference between source and trophic AA δ¹⁵N values in higher marine consumers is less than predicted from empirical studies of invertebrates and fish.
2. To evaluate CSIA-AA for estimating TP of cetaceans, we compared source and trophic AA δ¹⁵N values of multiple tissues (skin, baleen, and dentine collagen) from five species representing a range of TPs: bowhead whales, beluga whales, short-beaked common dolphins, sperm whales, and fish-eating (FE) and marine mammal-eating (MME) killer whale ecotypes.
3. TP estimates (TP_CSIA) using several empirically-derived equations and trophic discrimination factors (TDFs) were 1 to 2.5 trophic steps lower than stomach content-derived estimates (TP_SC) for all species. Although TP_CSIA estimates using dual TDF equations were in better agreement with TP_SC estimates for bowhead whales, belugas, and FE killer whales, our data do not support the application of a universal or currently available dual TDFs to estimate cetacean TPs. Discrepancies were not simply due to inaccurate TDFs, however, because the difference between consumer glutamic acid (Glu) and phenylalanine (Phe) δ¹⁵N values (δ¹⁵N_Glu-Phe) did not follow expected TP order, indicating it is not a reliable index of relative TP in these species.
4. In contrast with pioneering studies on invertebrates and fish, our data suggest trophic ¹⁵N enrichment of Phe is not negligible and should be examined among the potential mechanisms driving ‘compressed’ and variable δ¹⁵N_Glu-Phe values at high TPs. We emphasize the need for controlled diet studies to clearly understand mechanisms driving AA-specific isotopic fractionation before widespread application of CSIA-AA in ecological studies of cetaceans and other marine consumers.

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Author(s):

Matthews, Cory

Matthews, Cory

Fisheries and Oceans Canada

, Ruiz-Cooley, Iliana

Ruiz-Cooley, Iliana

Moss Landing Marine Laboratories

, Pomerleau, Corinne

Pomerleau, Corinne

Fisheries and Oceans Canada

, and Ferguson, Steven

Ferguson, Steven

Fisheries and Oceans Canada

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Source Repository:

Dryad

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URL:

https://doi.org/10.5061/dryad.9kd51c5d3

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Publication date:

2021-02-10

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Keywords:

Amino acids, isotopic fractionation, and marine consumers

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APA Citation:

Matthews, C., Ruiz-Cooley, I., Pomerleau, C., & Ferguson, S. (2021). Data from: Amino acid δ15N underestimation of cetacean trophic positions highlights poor understanding of isotopic fractionation in higher marine consumers [Data set]. Dryad. https://doi.org/10.5061/dryad.9kd51c5d3

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