High fidelity: isotopic relationship between stream invertebrates and their gut contents

Abstract

Benthic macroinvertebrate families were sampled along 3 rivers in New Brunswick, Canada. Stable isotopes of C and N were compared between body tissue and gut contents of individuals. d13C and d15N of body tissue and gut contents were strongly correlated (r 5 0.94 and 0.93, respectively) over a wide range of d values. In nonpredators, only minor fractionation of d13C and d15N was observed. In predators, diet-tissue fractionation of 13C was minor, but 15N fractionation that may have been related to diet quality (N content) was observed. The influence of diet quality on N-isotope fractionation was inconsistent in direction and strength among families. Our results suggest that subjecting primary consumers to gut clearance prior to processing for stable-isotope analysis is unnecessary, but the guts of predators should be removed before processing.