Recognizing Other Effective Area-based Conservation Measures (OECMs) is a critical pathway for achieving the global “30 × 30” biodiversity target. China pioneered the Marine Ecological Redline (MERL) system to safeguard key marine ecosystems, rare and endangered species, and critical habitats through large-scale, legally mandated spatial regulation. However, MERLs have not yet been systematically assessed against OECM criteria. This study evaluates the institutional attributes and ecological effectiveness of MERLs, using the Pearl River Estuary as a case study, and identifies potential OECMs across non-MERL areas in China. The results show that MERLs fully meet OECM criteria, with the Pearl River Estuary MERLs demonstrating marked improvements in water quality, biodiversity recovery, and control of marine development intensity. We provide the first empirical evidence that MERLs function as a nationally led institutional OECM model, which enriches the typology of OECMs and introduces a novel governance pathway for marine biodiversity protection. Furthermore, eight types of non-MERL spatial units were identified as potential marine OECMs. By implementing policy and economic incentive mechanisms and establishing tiered recognition and dynamic identification systems, China can further biodiversity conservation and contribute to the global 30% marine protection goal.

Marine spatial planning (MSP) has emerged as a fundamental process for achieving the balanced development of marine ecology, economy, and society. However, increasing conflicts among multiple marine uses, particularly between port development, industrial activities, fisheries, recreation, and ecological protection, highlight the pressing demand for robust and science-based planning tools. In this study, we propose an integrated analytical framework for multi-objective spatial suitability evaluation to optimize MSP. Using the coastal waters of Dalian, China, as a case study, we evaluated the spatial suitability of five key marine activities (ecological protection, mariculture, port construction, wind energy farm development, and coastal tourism) and applied a multi-criteria decision-making approach to inform spatial zoning. The results emphasize the region’s ecological significance as providing critical habitats and migratory corridors for protected and threatened species as well as fishery resources, while also revealing substantial spatial overlaps between conservation priorities and human activities, particularly in nearshore zones. The optimized zoning scheme classifies 22.0% of the coastal waters as Ecological Redline Zones, 32.4% as Ecological Control Zones, and 45.6% as Marine Exploitation Zones. This science-based spatial classification effectively reconciles ecological priorities with development needs, providing a spatially explicit and policy-relevant decision support tool for MSP.