Stable Isotope Composition of Fatty Acids in Organisms of Different Trophic Levels in the Yenisei River

Michail I Gladyshev,Galina S Kalachova,Nadezhda N Sushchik,Olesia N Makhutova,Jack Anthony Gilbert

doi:10.1371/journal.pone.0034059

Michail I Gladyshev, Galina S Kalachova + Show 3 more

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https://doi.org/10.1371/journal.pone.0034059

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Abstract

We studied four-link food chain, periphytic microalgae and water moss (producers), trichopteran larvae (consumers I), gammarids (omnivorous – consumers II) and Siberian grayling (consumers III) at a littoral site of the Yenisei River on the basis of three years monthly sampling. Analysis of bulk carbon stable isotopes and compound specific isotope analysis of fatty acids (FA) were done. As found, there was a gradual depletion in 13C contents of fatty acids, including essential FA upward the food chain. In all the trophic levels a parabolic dependence of δ13C values of fatty acids on their degree of unsaturation/chain length occurred, with 18:2n-6 and 18:3n-3 in its lowest point. The pattern in the δ13C differences between individual fatty acids was quite similar to that reported in literature for marine pelagic food webs. Hypotheses on isotope fractionation were suggested to explain the findings.

Highlights

Compound specific isotope analysis (CSIA) is comparatively new research tool for disentangling of natural food webs [1,2,3]
Fatty acid composition of studied organisms and groups did not differ from those obtained in previous periods [14,18,22]
Using fatty acid composition of storage lipids, triacylglycerols (TAG), it was found that the trichopterans in the Yenisei River primarily consumed diatoms and green algae [18], which were dominant species of the phytoperiphyton in the studied sites of the river [14,15,16,17]

Summary

Introduction

Compound specific isotope analysis (CSIA) is comparatively new research tool for disentangling of natural food webs [1,2,3]. CSIA appeared to be more successful than the other trophic markers in three cases: 1) when studied organisms cannot be physically isolated from each other; 2) if we need to trace quantitatively minor but qualitatively important component; 3) when different food sources have similar bulk carbon isotope and FA signatures. In the lower (marine) end of the estuary isotope signatures of bacterial and algal FA and POC were similar These differences in FA signatures indicated that in the upper part of estuary bacteria preferentially used non-algal allochthonous carbon of terrestrial origin, while in the marine part of the estuary the local production by phytoplankton may be an important source for bacterial growth [5]

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