Using MixSIAR to quantify mixed contributions of primary producers from amino acid?15N of marine consumers

Estimations of the trophic position and the food web nitrogen baseline from compound-specific isotope analysis of individual amino acids (CSIA-AA) are challenged when the diet of consumer organisms relies on different proportions of vascular and non-vascular primary producers. Here we propose a method to infer such proportions using mixing models and the delta 15N CSIA-AA values from marine herbivores. Combining published and new data, we first characterized CSIA-AA values in phytoplankton, macroalgae and vascular plants, and determined their characteristic beta values (i.e. the isotopic difference between trophic and source AA). Then, we applied MixSIAR Bayesian isotope mixing models to investigate the transfer of these isotopic signals to marine herbivores (molluscs, green turtles, zooplankton and fish), and their utility to quantify autotrophic sources. We demonstrated that primary producer groups have distinct delta 15NAA fingerprints that can be tracked into their primary consumers, thus offering a rapid solution to quantify resource utilization and estimate beta mix values in mixed-sourced environments.

Automated summary

This study proposes a method to infer the proportions of vascular and non-vascular primary producers in the diet of consumer organisms using mixing models and compound-specific isotope analysis. The research demonstrates that primary producer groups have distinct isotopic fingerprints that can be tracked into their primary consumers.