Using Stable Isotopes of Carbon and Nitrogen to Evaluate Trophic Interactions in Aquatic Environments

This paper describes a series of laboratory exercises for upper level biology courses, independent research and/or honors programs. Students sampled fish from a local water body with the assistance of a local fish and wildlife agency. Tissue samples from collected fish were utilized to obtain estimates of the stable isotopes delta[superscript 13]C and delta[superscript 15]N. An open-source mass balance model was utilized to estimate fish diets from isotope values. Isotopes were also used to measure trophic position (TP) and evaluate dietary niche overlap between native and introduced species. It was found that delta[superscript 15]N concentrations increased with each trophic level starting with benthic algae (lowest) to omnivores, then primary carnivores and ultimately piscivores (highest). Estimates of delta[superscript 13]C suggested all collected taxa utilized littoral habitats for feeding purposes. Native chain pickerel ("Esox niger") had the highest delta[superscript 15]N and TP estimates at 14.4 and 4.11, respectively. Nonnative largemouth bass ("Micropterus salmoides") delta[superscript 15]N and TP estimates were 13.56 and 3.86, respectively. Model estimates suggested that chain pickerel and largemouth bass diets were partitioned: pickerel consumed only fish and bass consumed principally invertebrates with some intermittent fish contributions. This lab helped integrate multiple disciplines, provide practical experience, and encourage critical-thinking skills while educating students about trophic ecology. (Contains 4 figures and 1 table.)