Careful definition and illustrative case studies are fundamental work in developing a Blue Economy. As blue research expands with the world increasingly understanding its importance, policy makers and research institutions worldwide concerned with ocean and coastal regions are demanding further and improved analysis of the Blue Economy. Particularly, in terms of the management connotation, data access, monitoring, and product development, countries are making decisions according to their own needs. As a consequence of this lack of consensus, further dialogue including this cases analysis of the blue economy is even more necessary. This paper consists of four chapters: (I) Understanding the concept of Blue Economy, (II) Defining Blue economy theoretical cases, (III) Introducing Blue economy application cases and (IV) Providing an outlook for the future. Chapters (II) and (III) summarizes all the case studies into nine aspects, each aiming to represent different aspects of the blue economy. This paper is a result of knowledge and experience collected from across the global ocean observing community, and is only made possible with encouragement, support and help of all members. Despite the blue economy being a relatively new concept, we have demonstrated our promising exploration in a number of areas. We put forward proposals for the development of the blue economy, including shouldering global responsibilities to protect marine ecological environment, strengthening international communication and sharing development achievements, and promoting the establishment of global blue partnerships. However, there is clearly much room for further development in terms of the scope and depth of our collective understanding and analysis.

The marine ecological red lines (MERLs) is an institutional innovation of the Chinese government to seek a balance between ecological protection and social development. China’s MERLs was designated in 2017, but there are problems such as insufficient consideration of areas of high ecological importance and lack of convergence with marine functional zoning. This paper carries out the adjustment of the MERLs in China by constructing the methods of marine ecological importance assessment and human activities disposal assessment, and the results show that after the adjustment, the type and distribution pattern of China’s MERLs is more reasonable, the areas of high ecological importance in the MERLs increases significantly, the intensity of human activities in the MERLs declines significantly, and the unification with the use of marine space is realized. China’s adjustment of the MERLs is based on scientific assessment and realizes the coordination of development and protection, which can provide a reference for global marine ecological protection.

Vegetated coastal wetlands, especially mangroves, seagrass beds, and salt marshes, are biodiversity-rich ecosystems whose blue carbon outcomes depend on living communities, sediment dynamics, hydrological connectivity, and landscape context. Biodiversity conservation and blue carbon management are often assessed through separate scientific, monitoring, and policy frameworks. This review uses a staged literature search and thematic synthesis to examine biodiversity–blue carbon linkages across the three major vegetated coastal wetland types. It considers how taxonomic, genetic, functional, and habitat diversity influence productivity, sediment stabilization, trophic exchange, carbon stocks, carbon burial, and carbon retention. It also evaluates how climate change, habitat fragmentation, hydrological alteration, pollution, and anthropogenic disturbance weaken these linkages. The synthesis compares representative carbon-stock and burial-rate baselines, examines conservation and restoration synergies and trade-offs, and expands the discussion of seagrass regime shifts. Field surveys, remote sensing, unmanned aerial vehicles, environmental DNA, and AI-enabled data integration are placed within a tiered monitoring framework. The review further develops an operational decision pathway for biodiversity-centered blue carbon management. Persistent blue carbon benefits arise where conservation and restoration maintain native communities, hydrological exchange, sediment stability, habitat complexity, migration space, and long-term stewardship capacity.

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.

Coastal salt marshes store substantial organic carbon, but strong heterogeneity in carbon density complicates upscaling for blue carbon accounting, national inventories, and restoration planning. Using a standardized monitoring dataset from 361 salt marsh sites across eight coastal provinces in China (2021–2024), we quantified sediment carbon density in the upper 0–1 m and biomass carbon density (aboveground and belowground), and evaluated plausible drivers. Carbon densities were highly skewed, with sediment carbon dominating the combined carbon density. Vegetation composition explained the strongest contrasts: Spartina spp.-dominated marshes exhibited higher sediment and combined carbon density than Phragmites spp. and Bulrush/Sedge (mixed Cyperaceae taxa; including Schoenoplectus spp., Bolboschoenoplectus spp., and Carex spp.) marshes, whereas Phragmites spp. marshes supported the highest total biomass carbon density. After adjustment for vegetation group, sampling year, and latitude, sediment carbon density showed a modest negative latitudinal trend. Sediment fine fraction had little marginal association with sediment carbon density, but emerged as a positive predictor of sediment and combined carbon density once geographic and compositional structure was accounted for, consistent with context-dependent texture effects. In contrast, total biomass carbon density showed limited covariate-adjusted association with either fine fraction or sediment carbon density, and biomass allocation metrics did not provide a direct proxy for sediment carbon density. These results support stratified monitoring, reporting and verification designs that use vegetation group as a first-order stratum and sediment texture as a secondary modifier to strengthen higher-tier, accounting-relevant reporting and restoration targeting.

Temperate seagrass carbon-stock data remain limited in northern China, especially for island meadow systems with mapped distribution and repeated field verification. This study quantified standing seagrass ecosystem carbon stocks in the Changshan Archipelago, Dalian, using a standardized field survey covering eight meadow zones, 39 sampling stations, and 323.37 ha of confirmed seagrass area. Plant biomass carbon and sediment organic carbon were assessed, and the 0–100 cm sediment profile was sampled at all stations. The mapped meadows stored 29,305.75 Mg C in total ecosystem carbon. Sediment organic carbon accounted for 28,965.71 Mg C, representing 98.84% of the total stock. Plant biomass carbon contributed 340.04 Mg C, or 1.16%. The area-weighted ecosystem carbon stock per unit area was 90.63 Mg C ha⁻¹. This per-area stock ranged from 52.11 Mg C ha⁻¹ in Xiaochangshan to 209.50 Mg C ha⁻¹ in Haiyang Island. Guanglu Island contained the largest total carbon stock, with 9247.73 Mg C, because of its large meadow area and relatively high per-area carbon stock. The results show how mapped meadow area, sediment carbon dominance, and local sediment setting jointly shape regional carbon-storage patterns. This standardized baseline provides field-based evidence for comparing northern Chinese seagrass meadows with other temperate Zostera systems. The estimates describe standing ecosystem carbon stocks. Annual carbon sequestration rates were outside the scope of the assessment.