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

Oct 15, 2026

This paper describes a sequence of laboratory exercises for upper-level biology students, independent research, and honors programs. With support from a local fish and wildlife agency, students sample fish, collect tissue, and estimate stable isotope values of 13C and 15N. An open-source mass balance model is used to infer fish diets from isotope signatures, calculate trophic position, and assess dietary niche overlap between native and introduced species. Results show predictable 15N enrichment across trophic levels and habitat-related 13C patterns.

LanguageEnglish

CategoryResearch & Report

FormatPDF

Pages6

Reading Time15 min

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Abstract

Introduction

Isotope Ecology

INNOVATIONS Using Stable Isotopes of Carbon and Nitrogen to Evaluate Trophic Interactions in Aquatic Environments David R Christensen* and Andrew LaRoche Biology Department, Westfield State University, Westfield, MA 01086 *Corresponding Author: [dchristensen@westfield.ma.edu](dchristensen@westfield.ma.edu) Abstract: 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 į13C and į 15N. 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 į15N concentrations increased with each trophic level starting with benthic algae (lowest) to omnivores, then primary carnivores and ultimately piscivores (highest) . Estimates of į13C suggested all collected taxa utilized littoral habitats for feeding purposes. Native chain pickerel (Esox niger) had the highest į15N and TP estimates at 14.4 and 4 . 11, respectively. Nonnative largemouth bass (Micropterus salmoides) į 15N 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 criticalthinking skills while educating students about trophic ecology. Key Words: Stable isotopes, trophic position, dietary niche, nonnative species INTRODUCTION Current pedagogical theory suggests an activeinquiry based approach to teaching can provide students with essential skills such as observation, hypothesizing, experimentation, analysis and synthesis (National Science Foundation, 1996; National Research Council, 2000). Often, inquirybased laboratory exercises are theory-based experimentation, rather than practical application of scientific understanding. Many students interested in environmental biology disciplines will eventually accept applied field-based positions where descriptive research is most commonly used. In fieldbased disciplines such as ecology, conservation biology, environmental biology, limnology, fisheries, and marine and wildlife biology, students often graduate deficient in necessary skills needed to compete in their fields (Millenbah and Millspaugh, 2003) . These skills could include sampling techniques, data management, data analysis, statistics, oral and written communication mastery, inquiry and critical thinking. Particularly, the ability to integrate these skills into a single approach has been cited as a major shortcoming in contemporary college graduates (Millenbah and Millspaugh, 2003) . A balance between experimental inquiry-based learning and applied/descriptive-based approaches should be considered to provide students more experiences appropriate to their future careers. In particular, an integration of multiple disciplines into one project, as would be common in real-life working scenarios, should be encouraged. In this paper we describe a series of laboratory exercises for upper-level biology, independent research and/or honors courses. The exercise involves students collecting fish taxa from a local pond, fixing tissue samples, managing large data sets, andreconstructing the local food web through the utilization of carbon and nitrogen isotopes and an open-source isotope model. Students are allowed to focus on particular components of the food web such as trophic structure, feeding behavior, resource partitioning and the potential for competition. At the end of the lab sequence students are familiar with common fish samp

FAQs

What stable isotopes are measured and how are they used in the lab?

Students obtain 13C and 15N estimates from fish tissue samples. 13C supports inferences about feeding habitat, while 15N is used to estimate trophic position and diet through enrichment patterns.

How is fish diet estimated from isotope values?

An open-source mass balance model is applied to the isotope measurements. The model converts isotope signatures into dietary estimates for collected taxa.

What comparisons does the lab enable between native and introduced species?

The lab uses trophic position (TP) and isotope-based diet estimates to evaluate dietary niche overlap between native and nonnative species, supporting analysis of trophic structure and potential competition.

Oct 15, 2026

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