Improved method for estimating trophic position of the coastal blooming moon jellyfish aurelia coerulea: considering large carbon trophic discrimination factors and diet contributions

Abstract

Stable isotope analysis (SIA) is an excellent tool for understanding ecology for several decades. In particular, the fact that trophic discrimination factors (TDFs) are generally constant in a given ecosystem (e.g., terrestrial or aquatic) has enabled SIA to determine trophic position (TP) and track energy sources. However, the exceptional cases of TDF make it challenging to understand marine food webs by SIA. In the food chain, jellyfish, a voracious predator, have received considerable attention because of their large biomass and their impact on competition with other organisms. However, because of the uncommon TDF of jellyfish, their ecological characteristics related to feeding and their niche or TP throughout their life cycles are marginal. In this study, the TP of the moon jellyfish Aurelia coerulea was calculated using a stable isotope approach. In particular, TP for polyps was calculated for the first time, and a TP of 1.9 was obtained using a general TDF. However, a method using a specific TDF was needed for medusae because of their specific nitrogen metabolism related to gelatinous accumulation. A new formula for the TP of medusae was based on the feasible TDF (4.2) of carbon isotope ratios along with its diet contributions. As a result, a TP of approximately 3.6 suggested that the medusae of A. coerulea occupies a relatively high position in the predator hierarchy, indicating more than 50% of contribution of Sagitta sp. to their diet. This study presents a improved approach for accurately estimating the TP using dietary contributions in coastal environments. © The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature 2025.