Trophic modeling of temperature, nutrient, and hypoxia dynamics on Japanese anchovy populations in Osaka Bay

Anchovy (Engraulis spp.) populations are globally important fishery resources that are being increasingly threatened by rising sea temperatures, nutrient decline, and hypoxia. In this study, we developed a novel Ecopath with Ecosim (EwE) model for Japanese anchovy (Engraulis japonicus) in Osaka Bay, integrating species-specific physiological responses to water temperature, nutrient availability, and dissolved oxygen across the food web. The model successfully reproduced long-term trends in biomass and catch, validated by PREBAL diagnostics and historical data. Sensitivity analyses revealed that moderate warming (+2°C) enhanced anchovy biomass, whereas excessive warming (+3°C) and severe nutrient reduction decreased biomass through prey scarcity and hypoxia-induced mortality. Moderate warming (+1°C) or moderate nutrient enrichment (×1.5) increased Japanese anchovy biomass. Excessive warming (+3°C) decreased biomass primarily due to prey loss, while excessive nutrient enrichment (×3.0) reduced biomass mainly through hypoxia. These findings emphasize the cascading interactions among nutrient dynamics, primary production, prey availability, and predator mortality under environmental stressors. Despite uncertainties, our modeling approach provides actionable insights for integrated coastal management and climate adaptation strategies, offering a practical tool for sustaining fishery resources in a changing ocean. This study applies EwE by explicitly integrating the physiological responses of primary producers to temperature and nutrient changes, as well as the responses of consumers to temperature and hypoxia effects. By validating this integrated formulation through single-stressor analyses, it provides a robust basis for future multi-stressor applications.