Tracking Trophic Interactions in Coldwater Reservoirs Using Naturally Occurring Stable Isotopes

Abstract
We measured signatures of naturally occurring stable isotopes of carbon (13C) and nitrogen (15N) in important invertebrate and fish taxa in two coldwater reservoirs in Colorado that had different food webs. One reservoir, Lake Granby, contained a large population of an opossum shrimp, Mysis relicta, and the other, Blue Mesa Reservoir, did not. We compared temporal dynamics of isotopic signatures of all taxa between lakes to quantify sources of variability in consumer signatures and to assess potential turnover rates of isotopic signatures in the top predator. Stable isotope signatures varied little across season or body size within most taxa, but large differences across reservoirs were observed. Nitrogen signatures of lake trout Salvelinus namaycush were enriched in larger individuals in both reservoirs, indicating increasing trophic position with body size. Carbon signatures in lake trout livers were consistently lower than those in muscle samples but did not change more rapidly than muscle sig...