Cross-border ocean governance under legal plurality: evidence from the Guangdong–Hong Kong–Macao Greater Bay Area

Cross-border ocean governance in the Guangdong–Hong Kong–Macao Greater Bay Area involves three distinct legal, judicial and administrative systems. This study examines how governance outputs produced in one jurisdiction become lawfully usable in another. Combining doctrinal legal analysis, qualitative institutional document analysis and public-record case analysis, the study develops an exploratory legal–institutional interface framework. The 2017 Pearl River Estuary palm stearin spill serves as the principal case, supplemented by the Macao Smart Maritime System and Zhuhai–Hong Kong fisheries enforcement. Spill records reveal a contested notification interval, subsequent departmental responses and continuing updates. In Macao, a published staff account describes how shared vessel information resolved a discrepancy relevant to a passage decision. Fisheries records link inter-agency communication, local inspection and cross-border handover. Together, these cases distinguish formal arrangements, authorised uses and documented practice, showing how output usability relates to specific tasks undertaken by receiving institutions. The findings inform conditional propositions about how coordination work, working relationships and responsibility allocation may support interface formation, maintenance and adjustment. They also support an institutional approach that assesses procedural improvements within existing powers and considers targeted rule changes where current instruments cannot provide the required legal effects. The study contributes a framework for examining cross-jurisdictional output use and propositions for further testing in operational settings.