Challenging trophic position assessments in complex ecosystems: Calculation method, choice of baseline, trophic enrichment factors, season and feeding guild do matter: A case study from Marquesas Islands coral reefs

Trophic position (TP) estimates for coral reef species in the Marquesas Islands vary significantly depending on the method used, the baseline organic matter source, and seasonal factors. This study found that TP estimates can differ by up to 1.7 levels for the same species when using different methods or baselines, such as macroalgae versus phytoplankton. The use of a conventional enrichment factor (3.4‰) or a variable one based on feeding guilds also led to discrepancies in TP values. Compound-specific isotope analysis using source amino acids produced TPs similar to those derived from macroalgae, while seasonal variations showed lower TPs in winter compared to summer, particularly for species with lower baseline TPs. These findings highlight the critical role of methodological choices and ecological context in accurately assessing trophic dynamics, which are essential for ecosystem-based management.

Letourneur, Y., Fey, P., Dierking, J., Galzin, R., & Parravicini, V. (2024). Challenging trophic position assessments in complex ecosystems: Calculation method, choice of baseline, trophic enrichment factors, season and feeding guild do matter: A case study from Marquesas Islands coral reefs. Ecology and Evolution, 14(7). Portico. https://doi.org/10.1002/ece3.11620