Dear MARMAN community, My co-authors and I are pleased to share with you our new study on southern elephant seals as sentinels of the changes occurring in the Southern Ocean. Nicolas Séon, Vinicius Robert, Clive R. McMahon, Robert G. Harcourt, Mark Hindell, Alexandra Scheubel, Gaël Guillou, Paco Bustamante, Baptiste Picard, Christophe Guinet. (2025) Elephant seals as sentinels of the ongoing changes affecting the Southern Ocean: Disentangling environmental and maternal effects on pup size and body condition, *Science of The Total Environment*, *997*, *180125* *Abstract: * The weaning mass of southern elephant seal pups (*Mirounga leonina*) is a key predictor of their first-year survival probability. However, variations in pup morphometric characteristics (length, mass and body condition i.e. the residual of the allometric relationship between log(mass) and log(length)) are strongly associated with mother's length and body condition. Leveraging a comprehensive long-term dataset (2006–2024) that integrates morphometric, isotopic, and environmental data, we applied a structural equation model to disentangle the direct and indirect drivers of pup phenotype at weaning. This approach reveals that pup length and mass are primarily determined by maternal length, while pup body condition is mainly shaped by the environmental conditions experienced by the mother during her pre-breeding trip. Our long-term dataset highlights a decline in pup weaning mass and length but an increase in their body condition despite an increase in the size of the breeding population. The concurrent decrease in pup blood *δ*13C and *δ*15N values, reflecting those of their mother, suggests shifts in southern hemisphere food webs and in the trophic ecology of Kerguelen southern elephant seals. We hypothesize that these changes are mainly linked to shifts in the composition of the phytoplankton community at the base of the trophic chains, which could have downstream effects on intermediate trophic levels and top predators, as well as a southward shift in female at-sea distribution confirmed by the tracking data. Please find the open access publication at: https://doi.org/10.1016/j.scitotenv.2025.180125 Dr Nicolas Séon, nicolas.seon@up.ac.za -- Dr Nicolas Séon Post-doctoral researcher University of South Africa (UNISA) & University of Pretoria (UP) Department of Zoology and Entomology - Room 3 - 31 Private Bag x 20, Hatfield, 0028 Pretoria, South Africa 078-611-0410 -- This message and attachments are subject to a disclaimer. Please refer to http://upnet.up.ac.za/services/it/documentation/docs/004167.pdf <http://upnet.up.ac.za/services/it/documentation/docs/004167.pdf> for full details.