Multiple markers reveal distinct life-history strategies in equatorial fish populations

Biological markers provide valuable life-history information to investigate fish population structure and connectivity. While individual markers offer important insights, combining multiple markers can deliver a more comprehensive understanding, reflecting complex ecological processes at different spatio-temporal scales. Our study aimed to address gaps in our understanding of life-history strategies, including growth responses, movement, and resource use of golden snapper (Lutjanus johnii) across the equatorial Indo-West Pacific. We analysed growth and chemical variation in otoliths, and stable isotope composition of eye lenses and muscle from 70 fish from the Riau Archipelago and Sorong. Otolith growth chronologies identified population-specific environmental drivers of annual growth, with sea surface temperature positively associated with growth in the Riau Archipelago, while fish growth in Sorong was linked to the Indian Ocean Dipole. Otolith elemental composition (Mg:Ca, Sr:Ca, Ba:Ca) revealed shared and regional patterns with age, associated with movement and habitat use. Stable isotopes of carbon (δ¹³C) and nitrogen (δ¹⁵N) in muscle and eye lens showed significant regional variation, while eye lens also revealed differences among life stages, providing complementary information on trophic niches and potential ontogenetic shifts in diet. By combining multiple markers, we uncovered intricate, scale-dependent, life-history processes shaping fish population structures and dynamics. Our research enhances the understanding of species' responses to environmental change, and supports the delineation of biologically relevant management units to inform effective conservation and management strategies from an important yet understudied region.