Use of a δ13C–δ15N relationship to determine animal trophic positions in a tropical Australian estuarine wetland

Abstract

AbstractStable isotope composition of organisms from different trophic groups collected from a semi‐isolated wetland pool in the Ross River estuary, northern Australia, was analysed to determine if there was a consistent relationship between δ13C, δ15N and trophic level that could be used to assign trophic positions. A strong linear negative relationship between δ13C and δ15N was detected for the three trophic levels considered (primary producers, primary consumers and secondary consumers). This relationship was consistent among trophic levels, differing only in height, that is, on δ15N values, which indicate trophic positions. A difference of 3.6–3.8‰ between trophic levels was present, suggesting a δ15N fractionation of approximately 3.7‰, a value slightly higher than the commonly assumed δ15N fractionation of approximately 3.4‰. The relationship between δ13C and δ15N was similar for invertebrate and fish primary consumers, indicating similar δ15N trophic fractionation for both groups, meaning trophic positions and trophic length could be reliably calculated based on either invertebrates or fish.