Developing an ecological indicator framework for anthropogenic underwater noise: a multi-level cascade from sensory disruption to ecosystem service impairment

Anthropogenic underwater noise is an increasingly pervasive environmental pressure affecting marine and freshwater ecosystems, yet its ecological consequences are rarely incorporated into operational indicator-based assessment frameworks. Although behavioral, physiological, and population-level responses to underwater noise have been extensively documented, a major challenge remains in translating this fragmented evidence into a mechanistically coherent and decision-oriented assessment system. This review synthesizes current evidence on acoustic characteristics, sensory detection mechanisms, biological responses, and ecological consequences of underwater noise and develops an evidence-informed, multi-level ecological indicator framework linking acoustic exposure to ecosystem-level impairment. The framework integrates six hierarchical levels—acoustic exposure, sensory disruption, behavioral modification, energetic and physiological reallocation, population-level consequences, and ecosystem function alteration—and links each level to measurable ecological indicators and corresponding assessment endpoints. Candidate indicators include acoustic exposure metrics, stress and physiological biomarkers, behavioral thresholds, recruitment and population responses, and changes in ecosystem functions and services. We further integrate hazard characterization, exposure assessment, dose–response relationships, indicator selection, and ecological risk characterization into a decision-oriented assessment pathway, with particular emphasis on chronic sub-lethal exposure and cumulative stressor interactions. By organizing mechanistic evidence across biological scales and translating it into measurable indicators and management-relevant assessment endpoints, the proposed framework provides a structured basis for incorporating underwater noise into ecological monitoring, environmental impact assessment, and ecosystem-based management. The framework also highlights key uncertainties, including species-specific sensitivity, threshold variability, and the limited standardization of acoustic–ecological response relationships, thereby identifying priorities for future validation and application.