Weak trophic position-body mass relationships undermine simple size-spectrum models for coral reefs

Weak trophic position-body mass relationships undermine simple size-spectrum models for coral reefs Delecambre Z. auteur aut IRD Ghilardi M. auteur aut IRD Barneche D. R. auteur aut IRD Adjeroud Mehdi auteur aut IRD Brandl S. J. auteur aut IRD Casey J. M. auteur aut IRD Kulbicki Michel auteur aut IRD Mercière A. auteur aut IRD Morais R. A. auteur aut IRD Morat F. auteur aut IRD Costesec E. P. auteur aut IRD Schiettekatte N. M. D. auteur aut IRD Vii J. auteur aut IRD Letourneur Y. auteur aut IRD Parravicini V. auteur aut IRD text journalArticle eng text/pdf reformatted digital access Unravelling food web dynamics across biological communities is a central goal of ecology. In size-structured ecosystems, the shape of trophic pyramids is often inferred from their size spectra-the distribution of biomass across body-mass classes. Size-spectrum analysis has become a popular tool to study ecosystem functioning in aquatic ecosystems, including coral reefs. However, the key assumption behind size spectra, that body size directly and positively correlates with trophic position, has rarely been evaluated in these systems. Here, we test this assumption by quantifying body mass, population densities and estimating trophic position from stable isotopes for 325 fish species across four Indo-Pacific locations. Consistent with prior studies, we found a positive relationship between biomass and body mass. However, weak and variable relationships between body mass and trophic position led to higher biomass in primary consumers than in predators, as expected in traditional bottom-heavy or diamond-shaped trophic structures. Our findings thus challenge previous reports of coral reef fish biomass prevalence in higher trophic levels (e.g. inverted biomass pyramids), supporting earlier suggestions that simple size-spectrum models do not adequately represent the trophic structure of reef fish communities. specialized trophic position biomass pyramid size spectrum community stable isotopes 036 020 021 Proceedings of the Royal Society B : Biological Sciences 293 2064 20252357 [10 p.] 2026 0962-8452 https://www.documentation.ird.fr/hor/fdi:010096374 10.1098/rspb.2025.2357 0962-8452 [F B010096374] https://www.documentation.ird.fr/hor/fdi:010096374 https://horizon.documentation.ird.fr/exl-doc/pleins_textes/2026-03/010096374.pdf IRD - Base Horizon / Pleins textes 2026-03-11 2026-03-11 fdi:010096374 fre