Aquatic Sciences Meeting, Albuquerque 2001

CS34 Trophic Dynamics

Date: Friday, February 16, 2001, Time: 9:00:00 AM

Location: Mesilla

Vander Zanden, M, J, University of California Davis, Davis, USA, jakevz@hotmail.com

Rasmussen, J, B, McGill University, Montreal, Canada, jrasmu@bio1.lan.mcgill.ca

Patterns of trophic fractionation for 15N and 13C in aquatic food webs

Use of stable isotope techniques to quantify food web relationships requires knowledge of the enrichment or depletion in 15N and 13C between prey and predator (known as trophic fractionation). In this study, we estimate trophic fractionation for three populations of lake trout (Salvelinus namaycush Walbaum) known to be dietary specialists. The mean values were + 3.49 ppt (±0.23; 1 SD) for nitrogen and + 0.05 ppt (±0.63) for carbon. We synthesize the previously published fractionation estimates from marine and freshwater systems. 13C fractionation was rather variable, ranging from -0.8‰ to 2.4. 15N fractionation averaged 3.4‰, with herbivores/detritivores exhibiting more variable fractionation than carnivores. The high levels of variability in 15N fractionation for herbivore/detritivores supports the use of primary consumers (rather than primary producers) as baseline indicator organisms for aquatic food web studies. We incorporate the observed variation associated with trophic fractionation into 15N-based estimates of trophic position and two-source isotope mixing models using 13C.

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Aquatic Sciences Meeting, Albuquerque 2001

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