Dataset for the paper: McCormick, M. I. & Smith S. A. Environmental degradation increases maternal cortisol and reduces offspring survival in the wild

Environmental degradation may propagate across generations through maternal stress, yet experimental field evidence of its fitness impacts remains scarce. This study investigates how habitat degradation and social crowding affect the coral reef fish Acanthochromis polyacanthus through maternal stress pathways. Observational data revealed that maternal cortisol levels are structured by the local environment: females nesting in degraded, bare-rock habitats or high-density social environments exhibited significantly higher blood cortisol concentrations than those in coral-rich areas. To establish causality, maternal cortisol was experimentally elevated using field-based implants. Offspring from stressed females were significantly smaller at emergence and exhibited slower growth trajectories over the first 20 days. Crucially, these phenotypic changes translated into demographic costs, with broods from cortisol-treated parents experiencing progressively higher mortality. These findings suggest that elevated maternal cortisol acts as a physiological constraint on reproductive investment rather than an adaptive signal. By demonstrating that environmental stressors propagate across generations via endocrine pathways, this study identifies a potent mechanism through which habitat degradation and social crowding may impair the recruitment dynamics, threatening the persistence of some reef fish populations.