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Article

Recognizing China’s Marine Ecological Redlines as Institutional Other Effective Area-Based Conservation Measures for Advancing the 30 × 30 Global Biodiversity Target

by
Rong Zeng
,
Wenhai Lu
*,
Yan Xu
,
Yangyi Ai
and
Jie Liu
National Marine Data and Information Service, Tianjin 300171, China
*
Author to whom correspondence should be addressed.
Sustainability 2025, 17(18), 8323; https://doi.org/10.3390/su17188323
Submission received: 5 August 2025 / Revised: 27 August 2025 / Accepted: 3 September 2025 / Published: 17 September 2025
(This article belongs to the Special Issue Environmental Behavior and Climate Change)
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Abstract

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.

1. Introduction

In recent years, the rate of biodiversity loss has reached unprecedented levels, posing severe challenges to ecosystem services, food security, and climate regulation. In response to this alarming trend, the Convention on Biological Diversity (CBD) adopted the Kunming–Montreal Global Biodiversity Framework (GBF) in 2022, which establishes the “30 × 30” target requiring the effective conservation and management of 30% of the world’s terrestrial and marine areas by 2030 [1]. This ambition is supported by the public [2]. However, currently, only approximately 17.6% of terrestrial and freshwater areas are under formal protection, while the global network of marine protected areas (MPAs), comprising about 16,660 sites, covers merely 8.4% of the world’s oceans and coastal zones [3]. To achieve the 30 × 30 target, the CBD has, for the first time, mandated that Parties not only expand the coverage of protected areas but also identify and incorporate Other Effective Area-based Conservation Measures (OECMs) into their national conservation strategies.
OECMs are defined as geographically delineated areas that deliver measurable biodiversity conservation outcomes through specific governance and management regimes, despite lacking formal protected area designation. Unlike protected areas that are established with conservation as their primary objective, OECMs are characterized by their conservation outcomes, irrespective of the original management intent [4]. Fundamentally, protected areas adopt a goal-oriented approach, whereas OECMs employ an outcome-based paradigm [5]. Relative to conventional protected areas, OECMs demonstrate enhanced inclusivity and diversity, effectively bridging spatial, ecological, and governance gaps in current conservation frameworks. Consequently, OECMs provide a complementary mechanism for developing integrated conservation systems that reconcile ecological integrity with socioeconomic equity [6,7].
While the OECM concept has gained international recognition in global biodiversity governance frameworks, its marine applications have progressed markedly slower than terrestrial counterparts. As of October 2024, only 211 marine OECMs have been reported among 6,464 total registered units across 15 countries and regions, representing just 0.12% of global marine coverage [3]. Current marine OECM implementation remains predominantly case-specific, with governance models focusing mainly on community-based co-management or indigenous stewardship systems [8,9,10]. Documented cases demonstrate limited scope, exemplified by Indonesia’s traditional fisheries zones, Canada’s seasonal fishery closures, Norway’s coral protection areas, and Mexico’s fishing refuges [11,12,13,14]. Existing research predominantly highlights OECMs’ contributions to participatory governance, traditional knowledge preservation, and cultural value maintenance. Conversely, the potential integration of state-managed conservation systems with stringent spatial regulations into the OECM framework remains poorly understood. Significant gaps persist in both theoretical frameworks for such institutional models [15] and methodological approaches for evaluating OECM suitability across marine spatial classifications and governance regimes [8,9].
China possesses exceptionally rich marine resources and diverse ecosystem types. In line with its commitment to ecological civilization, the country has established a comprehensive marine spatial governance system that prioritizes ecological conservation. This system classifies marine areas into two main categories: (1) marine ecological zones, designated primarily for the provision of ecosystem services and include the most valuable areas demarcated as Marine Ecological Redlines (MERLs), and (2) marine development zones, designated based on environmental carrying capacity for achieving efficient and intensive spatial utilization.
The MERL system constitutes the cornerstone of China’s marine spatial planning (MSP), and the word “redline” means that things are strictly managed or controlled in Chinese [16]. Characterized by legally binding enforcement and standardized monitoring protocols [17], it currently covers over 85,000 km2, accounting for 26% of China’s nearshore marine areas, protecting critical ecosystems such as mangroves, coral reefs, seagrass beds, salt marshes, major estuaries, and representative islands [18]. The MERLs show some degree of consistency with the OECM identification criteria [19]. The MERL framework not only establishes a domestic policy foundation for China’s 30 × 30 target attainment but also contributes empirical evidence for implementing global marine conservation targets.
Against this background, this study addresses two central research questions: (1) Do China’s MERLs collectively satisfy the OECM identification criteria, and can they constitute a state-regulated OECM category within international conservation frameworks? (2) What additional marine spatial units in China demonstrate potential OECMs, and what assessment framework could validate their qualification? To address these questions, this study (i) systematically assesses the compatibility between MERLs and OECMs, (ii) quantifies conservation outcomes and institutional function in representative MERLs, (iii) identifies non-MERL areas with potential marine OECMs, and (iv) evaluates recognition feasibility through policy–institutional analysis. Collectively, these efforts aim to provide actionable pathways for China’s 30 × 30 target implementation while advancing global OECM governance theory.

2. Methodology

2.1. Qualitative Analysis of MERLs’ Compliance with the OECM Criteria

This study systematically reviewed the technical procedures, delineation objectives, delineation outcomes, management policies, and governance measures associated with China’s MERLs, as well as relevant literature evaluating their effectiveness. Based on the ten OECM identification criteria [3], we analyzed the MERLs and the ten criteria one by one to evaluate the overall compliance with incorporating MERLs into the OECMs.

2.2. Quantitative Analysis of MERLs’ Compliance with the OECM Criteria

The quantitative analysis focused on two pivotal OECM identification criteria: C1 (effectiveness) and C2 (long-term sustainability). Employing the MERLs in the Pearl River Estuary as a case study, we assess protection effectiveness from 2016 to 2023 through four dimensions: seawater quality, benthic biodiversity, fisheries sustainability, and control of development intensity. This analysis validated the operational achievement of MERL statutory conservation targets while providing empirical evidence for OECM qualification.

2.2.1. Study Area

The Pearl River Estuary, located on Guangdong Province’s southern coast, is among China’s most significant estuarine ecosystems. Our study focuses on this 10,865 km2 estuary, where 3557 km2 are legally designated as MERLs (Figure 1). These MERLs contain ecologically critical habitats such as fish spawning grounds, estuaries, coral reefs, and mangroves, all of which maintain high biodiversity and provide vital ecosystem services. As the ecological core of the Guangdong–Hong Kong–Macao Greater Bay Area, the region faces substantial development pressures from maritime transport and fisheries. This combination of ecological importance and anthropogenic pressure makes the estuary an ideal case study for assessing MERLs’ effectiveness and OECM compatibility.

2.2.2. Evaluation Indicators

The adjustment of MERLs in the Pearl River Estuary was implemented from 2019 to 2023. We analyzed data from 2016, 2018, 2020, and 2023 to evaluate the system’s implementation effectiveness. Our assessment framework incorporated four key metrics (Table 1):
These indicators collectively evaluate protection effectiveness regarding water quality, benthic ecosystem status, fishery resource maintenance, and human activity impacts. They provide an integrated framework that captures ecological outcomes and governance effectiveness, ensuring that the evaluation reflects both biodiversity conservation and the institutional capacity of MERLs.

2.2.3. Analytical Methods and Data Analysis

The Pearl River Estuary was stratified into MERL and non-MERL areas for comparative analysis. Temporal trend analysis examined 2016–2023 indicator trajectories within MERLs to identify significant improvements in ecosystem structure and reductions in anthropogenic pressure intensity. Spatial contrast analysis quantified differential indicator trends between MERL and non-MERL areas to assess both relative conservation efficacy and regional-scale protection outcomes.
All quantitative data were statistically analyzed using descriptive statistics (mean ± standard deviation). Differences across years and between MERLs and non-MERLs were tested using one-way ANOVA with Tukey’s post hoc test (p < 0.05). Independent-sample t-tests were applied where appropriate for paired comparisons. Statistically significant differences are reported in the Results section and are denoted in figures with error bars and asterisks or letters according to statistical outputs.

2.3. Method for Identifying Potential Marine OECMs in Non-MERL Areas

To comprehensively assess whether marine areas outside the existing MERLs in China possess ecological, cultural, or other conservation value that could qualify them as OECMs, this study proposes the below identification framework (Figure 2).

2.3.1. Classification-Based Identification

The identification of potential marine OECMs in non-MERL areas integrated two complementary approaches. First, a spatial classification-based identification was applied to identify areas with existing regulatory restrictions or documented ecological management priorities in marine spatial plans. Second, management practice-based identification was used to capture areas that demonstrate measurable biodiversity outcomes through conservation actions such as ecological restoration, monitoring programs, community co-management, or cultural preservation initiatives, regardless of their formal zoning designations. Spatial planning-based identification provides a systematic and policy-oriented approach by embedding biodiversity objectives within legally recognized governance frameworks. However, this method may underestimate areas where conservation effectiveness arises from informal, customary, or community-driven practices. To address this limitation, we also employed a practice-based identification, ensuring that the two methods complemented each other and together enabled the more comprehensive identification of potential OECMs in non-MERL areas.

2.3.2. Conformity Assessment

Through criterion-based mapping analysis, this study systematically evaluated each identified marine spatial category against the ten OECM identification criteria. The assessment quantified compliance levels by comparing fulfilled versus unmet criteria per category, formulating the identification results of the potential OECMs in non-MERL areas of China.

3. Results

3.1. Compliance of MERLs with OECM Criteria

China has designated approximately 85,100 km2 of MERLs in its nearshore zone, including approximately 54,600 km2 of non-marine protected areas. The delineation of MERLs is grounded in a national marine ecological importance assessment, which identifies and prioritizes areas based on the ecological services function and ecological vulnerability. Specifically, three key dimensions guide the delineation: (1) marine biodiversity maintenance function; (2) marine coastal protection function; (3) coastal erosion and sand loss vulnerability [18]. Areas identified as extremely important and highly vulnerable are preferentially included within MERLs.
Assessment against the ten OECM criteria confirms that non-MPA portions of MERLs meet all required standards. First, governance and management are secured through State Council approval, with provincial governments responsible for implementation. MERL boundaries are clearly defined, embedded in national MSP and marine use approval systems, and supported by statutory policies that restrict damaging human activities [24]. Second, MERLs demonstrate strong ecological effectiveness. They encompass 99% of mangroves, 91% of coral reefs, and 89% of seagrass beds, thereby safeguarding key habitats that function as “blue ecological barriers” [25]. This habitat coverage indicates significant in situ biodiversity protection, while systematic monitoring and early-warning programs ensure adaptive management [26]. Third, MERLs safeguard ecosystem services and socio-cultural values, with extensive coverage of blue carbon ecosystems that contribute to national carbon neutrality goals and the protection of fish spawning grounds and estuaries that support sustainable fisheries [27]. Finally, MERLs’ incorporation into the Marine Environmental Protection Law and integration into MSP provide a stable institutional foundation for long-term sustainability [28].
Overall, MERLs represent a distinctive nationally led OECM model characterized by centralized governance, legally binding enforcement, stringent spatial controls, and explicit ecological prioritization. Compared to community-driven OECMs, this institutional framework provides systematic monitoring with quantifiable conservation outcomes, regulatory rigor through statutory mechanisms, and long-term effectiveness ensured by permanent institutional arrangements. These findings are summarized in Table 2, which presents the comparison between MERLs and the OECM criteria.

3.2. Comparative Analysis of MERL Protection Effectiveness in the Pearl River Estuary

A comparative analysis of four critical ecological parameters—dissolved oxygen (DO) levels, benthic biodiversity, larval fish density, and marine spatial use intensity—in the Pearl River Estuary from 2016 to 2023 reveals statistically significant environmental improvements within MERLs relative to adjacent unprotected areas. These findings demonstrate the MERL system’s operational effectiveness in (i) enhancing marine water quality, (ii) facilitating biological resource recovery, and (iii) mitigating anthropogenic development impacts. The consistent positive trends across indicators substantiate the conservation value of this regulatory approach in coastal ecosystem management.
In summer, the DO concentration within the MERLs increased from 5.08 mg/L in 2016 to 6.14 mg/L in 2020. Although it slightly decreased in 2023, it remained substantially higher than the 2016 level (Figure 3a). The Pearl River Estuary is one of China’s typical hypoxic zones due to high nutrient loading and the formation of a density stratification caused by low-salinity, high-temperature surface water overlying high-salinity, low-temperature bottom water. While the MERLs consistently exhibited slightly lower DO concentrations than adjacent non-MERL areas—attributable to their predominant location in nutrient-sensitive estuarine regions—the longitudinal data demonstrate substantial water quality improvement under this management regime.
In summer, the DO concentration within the MERLs increased from 5.08 mg/L in 2016 to 6.14 mg/L in 2020. Although it slightly decreased to 5.40 mg/L in 2023, it remained substantially higher than the 2016 level (Figure 3a). Statistical comparisons between MERL and adjacent non-MERL areas revealed a dynamic pattern: while the difference was not significant in 2016 (p = 0.116), the DO levels within the MERLs became significantly higher than those outside in both 2018 (p < 0.001) and 2020 (p = 0.002). However, this trend reversed in 2023, when the DO concentration was significantly higher outside the MERLs (p < 0.001). The Pearl River Estuary is one of China’s typical hypoxic zones due to high nutrient loading and the formation of density stratification. The earlier pattern of slightly lower DO concentrations within MERLs—attributable to their predominant location in nutrient-sensitive estuarine regions—was, thus, reversed during the mid-term of the study period, demonstrating substantial water quality improvement under this management regime before the unexpected shift in 2023. This reversal in 2023 suggests that broader environmental factors or regional management efforts may have occasionally over-ridden the local protection effect, highlighting the complex dynamics of estuarine hypoxia.
The macrobenthic diversity within the MERLs increased from 1.26 in 2016 to 1.77 in 2023, representing a 40% improvement (Figure 3b). Statistical comparisons revealed a dynamic interannual pattern in the protection effect: although the mean values were similar in 2016, the communities differed significantly (Welch’s t-test, p < 0.001). No significant difference was found between the areas in 2018 (p = 0.241). However, by 2023, the diversity within the MERLs became significantly higher than that outside (p = 0.002). This progression indicates that the implementation of the MERL system has effectively enhanced and solidified the protection of benthic habitats over time.
The trend in juvenile fish density closely mirrors that of macrobenthic diversity. Within the MERLs, it increased from 0.54 in 2016 to 1.24 in 2023. The difference compared to outside areas was significant in both 2016 (p = 0.003) and 2023 (p = 0.001), underscoring the consistent protective function of the MERLs as nursery grounds. No significant difference was observed in the interim year of 2018 (p = 0.717), likely reflecting the high natural variability in juvenile fish distribution. In contrast, the density outside the MERLs showed no consistent upward trend, further highlighting the effectiveness of the management regime.
Marine development intensity within the MERLs exhibited a clear downward trend. This indicator is a comprehensive management indicator, rather than an observation variable based on repeated sampling, and it, therefore, does not undergo formal statistical testing. Under the original regulations, high-intensity activities such as land reclamation and waste disposal were prohibited. In 2019, the Chinese government further clarified that, in principle, all developmental and construction activities are banned, with only limited uses permitted if they do not compromise ecological service functions. As a result, development intensity within the MERLs decreased sharply from 1.47 in 2018 to 0.63 in 2020—a reduction of more than 50%. Between 2020 and 2023, with regulatory mechanisms firmly established, intensity remained stable with a slight continued decline (Figure 3d).
In contrast, although areas outside the MERLs also showed a general downward trend, the rate of decrease was significantly lower. This indicates that the strict protection regime has been effective in curbing development intensity and mitigating anthropogenic disturbances within the MERLs.
The trend of the four indicators from 2016 to 2023 shows that the MERLs have achieved significant improvements in water quality, biodiversity restoration, and control of development intensity. Spatial distribution maps further reveal that the background situation of the MERLs in terms of biodiversity, juvenile fish density, and marine development intensity are generally superior to those outside. Moreover, the higher rate of improvement suggests that ecosystems within MERLs exhibit greater stability, resilience, and sustainability compared to adjacent areas (Figure 4). These findings highlight the overall effectiveness of MERLs as an institutional tool for ecological protection. The evaluation results offer empirical evidence supporting the alignment of MERLs with the OECM criteria C1 (effective) and C2 (long-term).

3.3. Identification Results of Potential Marine OECMs in Non-MERL Areas

Our analysis identified eight types of areas within China’s non-MERLs with varying potential to function as OECMs, categorized based on their spatial planning origin or management practices (Table 3). The assessment against the OECM criteria revealed a clear hierarchy of potential.
High-Potential Types: Three types exhibited the strongest alignment with the OECM criteria. Marine ecological zones provide biodiversity conservation through strict spatial regulations. Marine ecological restoration areas are project-based with monitored ecological targets. Marine cultural areas demonstrate effective, long-term biodiversity conservation outcomes enabled by stable socio-ecological governance systems.
Medium-Potential Types: This category includes specific-use zones within marine development zones—open aquaculture (non-feeding), traditional fishing (with limits), and natural landscape recreation areas. Their management generates ecological co-benefits but lacks dedicated monitoring, making outcomes unverifiable, and their governance is vulnerable to policy or economic shifts.
Low-Potential Types: Reserved areas and survey-identified ecologically important areas currently lack the necessary governance frameworks, legal security, or management focus to ensure long-term conservation, despite their spatial definition or recognized ecological value.

4. Discussion

4.1. The Complementary Value of MERLs as Nationally Led Institutional OECMs

The conceptual design of the OECM framework was originally intended to complement PA by addressing gaps in cultural diversity, community participation, and governance flexibility [8]. As a result, most current examples of OECMs are concentrated in areas governed or co-managed by communities or Indigenous peoples. To date, no centrally administered, top-down spatial model has been formally recognized as an OECM within the global framework.
Findings from this study indicate that MERLs, as a state-designated, ecologically prioritized, and legally enforced spatial planning instrument, demonstrate not only clear boundaries, well-defined conservation objectives, stable governance structures, and transparent regulatory policies but also verifiable ecological effectiveness. Our empirical evaluation confirms MERLs’ strong alignment with the OECM criteria, including governance legitimacy, effectiveness in biodiversity conservation, long-term sustainability, and the integration of ecosystem services, cultural values, and social benefits.
This study argues that MERLs represent a nationally led institutional OECM model. Through mechanisms such as spatial planning, use regulation, ecological monitoring and evaluation, and law enforcement, MERLs implement full-cycle, mandatory conservation management. The top-down, multi-agency coordination framework ensures sustainable governance capacity and provides a replicable model of biodiversity governance for other countries.
MERLs, thus, serve as both a key institutional foundation for China’s achievement of the “30 × 30” target and as a credible spatial unit for reporting OECM outcomes at the international level. More broadly, they enrich the typology of marine OECMs and offer an alternative to the dominant “community-based” pathway, demonstrating a viable “institutional OECMs” route for marine spatial governance.

4.2. Interpretation of MERL Protection Effectiveness and Limitation Reflection

Based on empirical research in the Pearl River Estuary, this study finds that areas within the MERLs perform better than those outside in terms of water quality improvement, biological recovery, and control of development intensity, with greater improvement observed. This indicates that the MERL system has played a positive role in protecting regional biodiversity. However, sustainable management and compliance are essential for ensuring the achievement of desired conservation outcomes [39], and several limitations should be acknowledged when interpreting these results.
First, baseline ecological differences may exist between MERL and non-MERL areas. For example, in certain years, the DO concentrations within MERLs were lower than those outside of them, which may reflect natural hydrodynamic conditions or salinity gradients rather than management effects alone. Second, there is a potential mismatch between historical monitoring stations and the finalized MERL boundaries, as the delineation was completed in 2023 while most monitoring networks were established earlier. This may affect the representativeness and spatial coverage of the evaluation results. Third, biodiversity recovery is an inherently long-term process, and some ecological indicators may display lag effects or natural fluctuations, particularly in relatively small-scale study areas. Fourth, while MERLs primarily emphasize ecological conservation, they currently integrate cultural and socioeconomic dimensions to a limited extent. This contrasts with many internationally recognized OECMs, where cultural diversity, community participation, and governance flexibility are central attributes. For example, the Velondriake Locally Managed Marine Area (LMMA) in Madagascar demonstrates how community-based governance, through periodic octopus fishery closures, has led to substantial increases in both catch and household income [40]. Compared with such bottom-up models, MERLs are state-led, legally enforceable, and operate at a much broader spatial scale, offering governance stability and scalability but showing weaker integration of cultural values and community participation. Strengthening inclusiveness in MERLs by incorporating local knowledge, cultural heritage, and participatory governance would, therefore, enhance their compatibility with the broader intent of the OECM framework.
Addressing these limitations will require targeted monitoring programs specifically designed for different types and conservation objectives of MERLs, including using technologies such as remote sensing and unmanned aerial vehicles. In addition, incorporating cultural and community-based values into management objectives would strengthen the holistic governance attributes of MERLs. Furthermore, climate change represents an additional uncertainty factor that could alter baseline ecological conditions. Sea level rise, ocean warming, and hypoxia events may influence dissolved oxygen and biodiversity trends irrespective of conservation measures. Incorporating climate resilience assessments into the MERL monitoring framework will, therefore, be crucial to ensuring their long-term effectiveness as OECMs.

4.3. Pathways and Challenges in the Recognition of OECMs in Non-MERL Areas

Beyond MERLs, there are numerous spatial units in China that demonstrate “substantial conservation effectiveness.” Based on two major paths, this study identifies eight types of areas with potential for marine OECMs and evaluates their compatibility with OECM criteria to assess their potential level.
However, further research is required in the following areas:
1. Lack of data to support conservation effectiveness evaluation. Many of these areas, while engaged in some ecological management practices, have not yet undertaken long-term, systematic ecological monitoring. As such, it is difficult to meet OECM criteria for protection effectiveness. The key activity to inform effective management is a robust biodiversity monitoring program [41]. We explicitly acknowledge that the insufficiency of monitoring data is currently a major barrier to supporting the formal recognition of non-MERL areas as OECMs and calls for their integration into the national ecological monitoring network.
2. Uncertainty in long-term institutional stability. In ecological restoration areas and newly identified important habitats, there is uncertainty regarding governance entities for future spatial management, which poses a risk of potential changes in usage. This makes it challenging to meet OECM criteria for stable governance systems. Potential governance risks may also arise from shifts in policy priorities or economic incentives, underlining the need for stronger legal recognition and safeguards to ensure continuity.
3. Cultural and socioeconomic values also play a critical role in the recognition of potential OECMs. Areas such as traditional fishing grounds, cultural seascapes, and marine tourism zones may provide biodiversity benefits while simultaneously maintaining cultural heritage and local livelihoods. These values strengthen local stewardship, enhance social legitimacy, and complement ecological functions, thereby increasing the robustness of OECM outcomes.
In the future, the recognition of OECMs in non-MERL areas will serve as an effective supplementary measure for China’s achievement of the 30 × 30 target. This process will require the design of policy and economic incentive mechanisms to mobilize various area owners and users in regions with potential OECMs. These stakeholders should aim to incorporate biodiversity protection and ecosystem service functions as secondary objectives alongside natural resource use, management, and economic activities, forming a multi-stakeholder OECM incentive system.
For instance, the legal status of OECMs could be clarified, integrating OECMs into the nationally recognized conservation system to ensure long-term stability in the management regime once an area is designated as an OECM. Additionally, funding support, granting marine concession rights, and ecological product certification support could guide governance entities toward exploring green, intensive, and eco-friendly development models, internalizing the external biodiversity conservation goals. Finally, a tiered recognition and dynamic identification mechanism could be established, progressing potential OECMs toward formal recognition. Based on the ecological value and protection effectiveness assessment, differentiated ecological compensation standards could be created, with periodic compensation provided to the entities responsible for OECM management and protection.

5. Conclusions

China’s MERLs, as a spatial management mechanism with strong institutional control, fully align with the identification criteria of OECMs. Based on empirical analysis of four ecological indicators in the Pearl River Estuary, this study demonstrates that areas within the MERLs have achieved significant and sustained improvements in water quality, biodiversity restoration, and control of development intensity. These results underscore the effectiveness and representativeness of MERLs as a conservation model.
This form of “nationally led institutional OECMs” provides a new category that should be formally recognized within the global OECM framework. It expands the typological spectrum beyond traditional community-based approaches and offers a replicable governance model for MSP and biodiversity protection globally.
Furthermore, through two identification pathways—spatial planning and management practices—this study identifies eight types of potential marine OECMs in non-MERL areas. These areas demonstrate varying levels of alignment with OECM criteria in terms of development intensity, governance strength, and ecological protection outcomes.
To fully realize their potential, targeted policy and economic incentive mechanisms should be designed to establish a legal status for OECMs, implement tiered recognition and dynamic identification systems, and incorporate ecological compensation schemes. These steps will mobilize diverse stakeholders to integrate biodiversity conservation into land and marine use decisions, thereby supporting the achievement of the “30 × 30” target and enhancing China’s contribution to global biodiversity governance.

Author Contributions

All authors contributed to the study conception and design. Conceptualization, material preparation, data collection and methodology were performed by R.Z., Y.X. and J.L. Data curation and methodology were also performed by R.Z., Y.X. and Y.A. The manuscript was revised by R.Z. and W.L. The formal analysis was performed and the first draft of the manuscript was written by R.Z. Reviewing and editing, validation, resource acquisition, project administration, and funding acquisition were performed by W.L. All authors commented on previous versions of this manuscript. All authors have read and agreed to the published version of the manuscript.

Funding

This research was financially supported by the National Key Technologies Research and Development Program of China [grant numbers 2023YFC3108003]; the National Marine Data and Information Service: “Revealing the List and Taking the Lead” project—Research on Ecological Evaluation Techniques Based on Marine Ecological Zones.

Data Availability Statement

The data used in this study are available upon request from the corresponding author.

Conflicts of Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

References

  1. CBD Secretariat. Kunming-Montreal Global Biodiversity Framework. Convention on Biological Diversity, Montreal. 2022. Available online: https://www.cbd.int/article/cop15-final-text-kunming-montreal-gbf-221222 (accessed on 20 August 2025).
  2. Fitzsimons, J.A.; Garrison, K.; Finnegan, B.; Luby, I. The 30 × 30 Protection Target: Attitudes of Residents from Seven Countries. Sustainability 2025, 17, 3444. [Google Scholar] [CrossRef]
  3. UNEP-WCMC; IUCN. Protected Planet Report 2024; UNEP-WCMC and IUCN: Cambridge, UK, 2024; Available online: https://www.protectedplanet.net/en/resources/global-protected-planet-reports (accessed on 20 August 2025).
  4. IUCN-WCPA. Recognising and Reporting Other Effective Area-Based Conservation Measures; IUCN-WCPA: Gland, Switzerland, 2019; Available online: https://portals.iucn.org/library/node/48887 (accessed on 20 August 2025).
  5. Jin, T.; Bu, J.Y.; Ma, J.Z. Other-effective area-based measures of global experiences and implications for post-2020 biodiversity conservation in China. J. West China For. Sci. 2022, 51, 1–8. [Google Scholar] [CrossRef]
  6. Maxwell, S.L.; Cazalis, V.; Dudley, N.; Hoffmann, M.; Rodrigues, A.S.L.; Stolton, S.; Visconti, P.; Woodley, S.; Kingston, N.; Lewis, E.; et al. Area-based conservation in the twenty-first century. Nature 2020, 586, 217–227. [Google Scholar] [CrossRef] [PubMed]
  7. Zhao, W.Y.; Wang, W.; Ma, B.R. Advances and prospects in research on Other Effective Area-Based Conservation Measures (OECMs). Biodivers. Sci. 2025, 33, 24525. [Google Scholar] [CrossRef]
  8. Jonas, H.D.; Barbuto, V.; Jonas, H.C.; Kothari, A.; Nelson, F. New steps of change: Looking beyond protected areas to consider other effective area-based conservation measures. Parks 2014, 20, 111–128. [Google Scholar] [CrossRef]
  9. Wall, J.; Moola, F.; Lukawiecki, J.; Roth, R. Indigenous-led conservation improves outcomes in protected areas. Nat. Rev. Biodivers. 2025, 1, 411–412. [Google Scholar] [CrossRef]
  10. Dunshea, G.; Olaussen, K.; Eckbo, N.H. Potential marine Other Effective Area-Based Conservation Measures (OECMs) in Norway: Current compliance status in relation to CBD and IUCN guiding principles, definitions and criteria. NTNU Vitenskapsmuseet Naturhistorisk Rapp. 2024, 3, 1–71. Available online: https://www.ntnu.no/documents/10476/1350233483/2024-3%2BRapport%2BOECM.pdf (accessed on 20 August 2025).
  11. Estradivari, D.S.; Adhuri, D.S.; Ferse, S.C.A.; Sualia, I.; Andradi-Brown, D.A.; Campbell, S.J.; Ahmadia, G.N. Marine conservation beyond MPAs: Towards the recognition of other effective area-based conservation measures (OECMs) in Indonesia. Mar. Policy 2022, 137, 104939. [Google Scholar] [CrossRef]
  12. Nancy, L.S.; David, M.K.; Heike, K.T. Challenges of Gauging the Impact of Area-Based Fishery Closures and OECMs: A Case Study Using Long-Standing Canadian Groundfish Closures. Front. Mar. Sci. 2021, 8, 612859. [Google Scholar] [CrossRef]
  13. Singleton, R.L.; Govan, H.; Jupiter, S.D. Reaching global marine biodiversity conservation goals with area-based fisheries management. Nat. Ecol. Evol. 2022, 6, 1120–1129. [Google Scholar] [CrossRef]
  14. Perera-Valderrama, S.; Rosique-de la Cruz, L.O.; Caballero-Aragón, H.; Cerdeira-Estrada, S.; Martell-Dubois, R.; Ressl, R. Mexico on Track to Protect 30% of Its Marine Area by 2030. Sustainability 2023, 15, 14101. [Google Scholar] [CrossRef]
  15. OECD. Biodiversity: Finance and the Economic and Business Case for Action; OECD Publishing: Paris, France, 2019; Available online: https://www.oecd.org/en/publications/biodiversity-finance-and-the-economic-and-business-case-for-action_a3147942-en.html (accessed on 26 August 2025).
  16. Bai, Y.; Jiang, B.; Wang, M.; Li, H.; Alatalo, J.M.; Huang, S.F. New ecological redline policy (ERP) to secure ecosystem services in China. Land Use Policy 2015, 55, 348–351. [Google Scholar] [CrossRef]
  17. Gao, J.; Zou, C.; Zhang, K.; Xu, M.; Wang, Y. The establishment of Chinese ecological conservation redline and insights into improving international protected areas. J. Environ. Manag. 2020, 264, 110505. [Google Scholar] [CrossRef]
  18. Zeng, R.; Xu, Y.; Yang, L.; Ai, Y.Y.; Liu, J.; Liu, C.; Lu, W.H. Adjustment of the marine ecological red lines in China. Sci. Rep. 2024, 14, 19247. [Google Scholar] [CrossRef]
  19. IUCN-WCPA. Guidance on Other Effective Area-Based Conservation Measures (OECMs). Technical Report No. 36. IUCN. 2023. Available online: https://portals.iucn.org/library/node/51272 (accessed on 26 August 2025).
  20. Borja, A.; Chust, G.; Muxika, I. Forever young: The successful story of a marine biotic index. Adv. Mar. Biol. 2019, 82, 93–127. [Google Scholar] [CrossRef] [PubMed]
  21. Lv, W.W.; Zhou, W.Z.; Zhao, Y.L. Effect of freshwater inflow on self-restoration of macrobenthic diversity in seaward intertidal wetlands influenced by reclamation projects in the Yangtze estuary, China. Mar. Pollut. Bull. 2019, 138, 177–186. [Google Scholar] [CrossRef] [PubMed]
  22. GB/T 42631-2023; Guideline for Marine Ecosystem Health Assessment in Nearshore Area. Standardization Administration of China: Beijing, China, 2023. Available online: https://openstd.samr.gov.cn/bzgk/gb/newGbInfo?hcno=E8345691E682255B0B0AEEBD5094135D (accessed on 26 August 2025).
  23. The National Development and Reform Commission. Notice on Issuing Technical Methods for Monitoring and Early Warning of Resource and Environmental Carrying Capacity (Trial). 2016. Available online: https://www.gov.cn/govdata/gov/201609/29/390288/article.html (accessed on 26 August 2025).
  24. The Ministry of Natural Resources; The Ministry of Ecology and Environment; The National Forestry; Grassland Administration. Notice on Strengthening Ecological Protection Red Lines Management. 2022. Available online: https://www.gov.cn/zhengce/zhengceku/2022-08/20/content_5706169.htm (accessed on 26 August 2025).
  25. The State Council Information Office of the People’s Republic of China. Marine Eco-Environmental Protection in China; Foreign Languages Press: Beijing, China, 2024. Available online: http://www.scio.gov.cn/zfbps/zfbps_2279/202407/t20240711_854815.html (accessed on 26 August 2025).
  26. The General Office of the Ministry of Natural Resources. Notice on Establishing and Improving the Marine Ecological Early Warning and Monitoring System. 2021. Available online: https://gi.mnr.gov.cn/202108/t20210805_2675229.html (accessed on 26 August 2025).
  27. China Land Surveying and Planning Institute. Blue Book of China’s Ecological Protection Redlines; China Earth Press: Beijing, China, 2023; pp. 27–28. [Google Scholar]
  28. Standing Committee of the National People’s Congress. Law of the People’s Republic of China on Marine Environmental Protection (Revised Version). 2023. Available online: http://www.npc.gov.cn/c2/c30834/202310/t20231024_432550.html (accessed on 26 August 2025).
  29. Wang, X.Q.; Deng, Y. Key issues and advancement strategies for China’s OECMs in alignment with the Kunming-Montreal Global Biodiversity Framework. Biodivers. Sci. 2025, 33, 24569. [Google Scholar] [CrossRef]
  30. The Ministry of Natural Resources. Notice on Issuing the Measures for the Control of Natural Ecological Space Use (Trial). 2017. Available online: http://www.mnr.gov.cn/gk/tzgg/201704/t20170424_1992172.html (accessed on 26 August 2025).
  31. The State Council of the Communist Party of China. Opinions of the Central Committee of the Communist Party of China and the State Council on Establishing a Territorial Spatial Planning System and Supervising Its Implementation. 2019. Available online: https://www.gov.cn/zhengce/2019-05/23/content_5394187.htm (accessed on 26 August 2025).
  32. Li, Y.P.; Liu, D.H.; Jiang, W.; Chi, Y. Insights on key issues of marine space use control from the perspective of territorial space planning. J. Nat. Resour. 2022, 37, 895–909. [Google Scholar] [CrossRef]
  33. The General Office of the Ministry of Natural Resources. Notice on Issuing the Guidelines for the Compilation of the Overall Planning of Municipal Land and Space (Trial). 2020. Available online: https://gi.mnr.gov.cn/202009/t20200924_2561550.html (accessed on 26 August 2025).
  34. Yu, J.; Hu, Q.W.; Yuan, H.R.; Tong, F.; Chen, P.M.; Mao, J.M. Effects assessment of summer fishing moratorium in Daya Bay in the Northern South China Sea. J. Geosci. Environ. Prot. 2017, 5, 96–108. [Google Scholar] [CrossRef]
  35. Zou, J.Y.; Jin, X.S.; Shan, X.J.; Ren, Y.P.; Chen, Y.L. Whether the summer fishing moratorium can improve the status of fisheries resources in the Yellow Sea and Bohai Sea. Heliyon 2024, 10, e38100. [Google Scholar] [CrossRef]
  36. The General Office of the Ministry of Natural Resources. Notice on Strengthening the Standardized Implementation and Supervision Management of National Land Space Ecological Restoration Projects. 2023. Available online: https://gi.mnr.gov.cn/202303/t20230306_2777533.html (accessed on 26 August 2025).
  37. Fei, X.Y.; Chen, Y.Q.; Kong, X.P. Cultural landscapes recognition and landscape genetic information chain analysis of traditional villages: A case study of Tanka Fishing village in Lingshui Li autonomous county. J. Nat. Resour. 2024, 39, 1760–1779. [Google Scholar] [CrossRef]
  38. Edvardsson, R.; Hjörleifsson, E.; Ólafsdóttir, Á.G. Synergies between underwater cultural heritage and biodiversity conservation in Iceland: Insights for achieving 30 × 30 targets. Mar. Policy 2025, 180, 106782. [Google Scholar] [CrossRef]
  39. Graham, J.E.; McCauley, D.J.; Trebilco, R.; Duarte, C.M.; Palumbi, S.R. Global conservation outcomes depend on marine protected areas with five key features. Nature 2014, 506, 216–220. [Google Scholar] [CrossRef]
  40. Oliver, T.A.; Oleson, K.L.L.; Ratsimbazafy, H.; Raberinary, D.; Benbow, S.; Harris, A. Positive catch & economic benefits of periodic octopus fishery closures: Do effective, narrowly targeted broader management? PLoS ONE 2015, 10, e0129075. [Google Scholar] [CrossRef]
  41. Dalton, D.T.; Berger, V.; Adams, V.; Botha, J.; Halloy, S.; Kirchmeir, H.; Sovinc, A.; Steinbauer, K.; Svara, V.; Jungmeier, M. A Conceptual Framework for Biodiversity Monitoring Programs in Conservation Areas. Sustainability 2023, 15, 6779. [Google Scholar] [CrossRef]
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Figure 1. The study area.
Figure 1. The study area.
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Figure 2. Method for identifying potential marine OECMs in non-MERL areas.
Figure 2. Method for identifying potential marine OECMs in non-MERL areas.
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Figure 3. A comparison of key ecological indicators within and outside the MERLs in the Pearl River Estuary from 2016 to 2023—(a): DO concentration; (b): macrobenthic diversity; (c): juvenile fish density; (d): marine development intensity. Error bars represent mean ± standard error of the mean (SEM). Significant differences between groups within each year were determined via Welch’s t-test ** p < 0.01, *** p < 0.001; ns, not significant.
Figure 3. A comparison of key ecological indicators within and outside the MERLs in the Pearl River Estuary from 2016 to 2023—(a): DO concentration; (b): macrobenthic diversity; (c): juvenile fish density; (d): marine development intensity. Error bars represent mean ± standard error of the mean (SEM). Significant differences between groups within each year were determined via Welch’s t-test ** p < 0.01, *** p < 0.001; ns, not significant.
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Figure 4. The spatial distributions of four indicators in the Pearl River Estuary in 2016 and 2023: (a) DO concentration in 2016; (b) DO concentration in 2023; (c) macrobenthic diversity in 2016; (d) macrobenthic diversity in 2023; (e) juvenile fish density in 2016; (f) juvenile fish density in 2023; (g) marine development intensity in 2018; (h) marine development intensity in 2023.
Figure 4. The spatial distributions of four indicators in the Pearl River Estuary in 2016 and 2023: (a) DO concentration in 2016; (b) DO concentration in 2023; (c) macrobenthic diversity in 2016; (d) macrobenthic diversity in 2023; (e) juvenile fish density in 2016; (f) juvenile fish density in 2023; (g) marine development intensity in 2018; (h) marine development intensity in 2023.
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Table 1. Indicators for evaluating MERLs’ protection effectiveness.
Table 1. Indicators for evaluating MERLs’ protection effectiveness.
NumberIndicatorsPolarityMeaningOperational DefinitionData SourcesYears
1Dissolved oxygen concentration+essential for marine organism survival and ecosystem functioningMean of each monitoring station in summerNational Marine Ecological Monitoring Network2016, 2018, 2020, 2023
2Macrobenthic diversity ( H ′ )+an established benthic habitat indicator given these organisms’ long life cycles and sedentary nature [20] H ′ = − ∑ P a ln P a
Pa:   proportion of species in total biomass
[21]		National Marine Ecological Monitoring Network2016, 2018, 2023
3Juvenile fish density +represents fishery resource productivity and sustainability [22]Mean of each monitoring station in summerNational Marine Ecological Monitoring Network2016, 2018, 2023
4Marine development intensity−calculated as the weighted area ratio of sea use types to total area, indicating anthropogenic pressure Marine   development   intensity   = ∑ A k   ×   w k /A
Ak: the area of the k-th type of sea use in the MERLs
wk: weight coefficients of the k-th type of sea use, indicating the impact intensity of the k-th type of sea use
A: Area of the MERLs
[23]		Sea Use Dynamic Monitoring System2018, 2020, 2023
Table 2. The compatibility of China’s MERLs with the OECM criteria.
Table 2. The compatibility of China’s MERLs with the OECM criteria.
OECM CriteriaKey RequirementMERL ComplianceCompatibility
A1. Not a PAIndependence of the legal PA system54,600 km2 MERLs outside PA system.Yes
B1. Geographically defined spaceClearly defined spatial boundariesLegally delineated, integrated into national MSPYes
B2. Legitimate governance authoritiesLegal governance rightsApproved by the State Council, implemented by provincesYes
B3. ManagedExistence of management systems regimeNational policies restrict damaging activitiesYes
C1. EffectiveDemonstrated biodiversity effectivenessHigh habitat coverage, improved wetland protection, quantitative evidence (see Section 3.2)Yes
C2. Long-term impactsLong-term sustainabilityIncorporated into national law and MSPYes
C3. In situ biodiversity protectionProtects biodiversity in situprotect areas with high biodiversity maintenance function, coastal protection function, sand loss, and erosion vulnerabilityYes
C4. Information and monitoringOngoing monitoring and reportingEcological early-warning monitoring and human activity monitoring systemsYes
D1. Ecosystem functions and servicesSafeguards ecosystem functionsCovers 97% of the high-ecological-importance and vulnerability areas.Yes
D2. Cultural, spiritual, socioeconomic, and other locally relevant valuesRecognizes local cultural and socioeconomic valueBlue carbon habitats, fishery spawning grounds and estuaries contribute to carbon goals and fishery resources sustainable developmentYes
Table 3. Potential marine OECM assessment results for non-MERL areas in China.
Table 3. Potential marine OECM assessment results for non-MERL areas in China.
Area TypeBrief Description and Rationale (With Key References)OECM Criteria—FulfilledOECM Criteria—Not FulfilledPotential Level
Marine ecological zonesStatutorily defined zones for ecological services (e.g., natural coastlines, spawning grounds) [29], often adjacent to MERLs. Feature strict prohibitions on high-intensity activities and clear regulatory mandates [30,31,32].A1, B1, B2, B3, C1, C2, C3, D1, D2C4High
Marine development zones—reserved areasAreas temporarily withheld from development for future projects. While their current state aids ecosystem recovery, they lack conservation mandates and are highly vulnerable to future conversion [33].A1, B1, B2, B3, C1C2, C3, C4, D1, D2Low
Marine development zones—open aquaculture (non-feeding)Designated zones for ecologically low-impact aquaculture that relies on natural productivity. Avoid eutrophication risks and maintain near-natural trophic structures, but lack long-term ecological monitoring targets.A1, B1, B2, B3, C1, C3, D2C2, C4, D1Medium
Marine development zones—traditional fishing areas (with limited measures)Areas subject to seasonal or spatial fishing restrictions to promote stock sustainability. Management provides ecological benefits but is primarily socioeconomic; continuity is subject to policy change [34,35].A1, B1, B2, B3, C1, C3, D2C2, C4, D1Medium
Marine development zones—recreational areas (natural landscape)Zones managed for tourism within ecological carrying capacity to preserve natural seascapes. Controls human disturbance but lacks formal biodiversity targets and monitoring to verify conservation outcomes.A1, B1, B2, B3, C1, C3, D2C2, C4, D1Medium
Marine ecological restoration areasProject-based interventions on degraded ecosystems (e.g., mangrove restoration) with defined boundaries, clear ecological targets, and post-project monitoring. Long-term governance stability can be funding-dependent [25,36].A1, B1, B2, C1, C3, C4, D1, D2B3, C2High
Ecologically important areas (identified via survey/assessment)Sites of documented ecological significance (e.g., key habitats, corridors) identified through scientific research. While spatially identifiable, they currently lack any dedicated governance, management, or monitoring framework.A1, B1, C1, C3, D1B2, B3, C2, C4, D2Low
Marine cultural areasAreas where traditional community practices impact conserve biodiversity through stable, culturally embedded governance and low-impact resource use [37,38].A1, B1, B2, B3, C1, C3, D1, D2C2, C4High
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Zeng, R.; Lu, W.; Xu, Y.; Ai, Y.; Liu, J. Recognizing China’s Marine Ecological Redlines as Institutional Other Effective Area-Based Conservation Measures for Advancing the 30 × 30 Global Biodiversity Target. Sustainability 2025, 17, 8323. https://doi.org/10.3390/su17188323

AMA Style

Zeng R, Lu W, Xu Y, Ai Y, Liu J. Recognizing China’s Marine Ecological Redlines as Institutional Other Effective Area-Based Conservation Measures for Advancing the 30 × 30 Global Biodiversity Target. Sustainability. 2025; 17(18):8323. https://doi.org/10.3390/su17188323

Chicago/Turabian Style

Zeng, Rong, Wenhai Lu, Yan Xu, Yangyi Ai, and Jie Liu. 2025. "Recognizing China’s Marine Ecological Redlines as Institutional Other Effective Area-Based Conservation Measures for Advancing the 30 × 30 Global Biodiversity Target" Sustainability 17, no. 18: 8323. https://doi.org/10.3390/su17188323

APA Style

Zeng, R., Lu, W., Xu, Y., Ai, Y., & Liu, J. (2025). Recognizing China’s Marine Ecological Redlines as Institutional Other Effective Area-Based Conservation Measures for Advancing the 30 × 30 Global Biodiversity Target. Sustainability, 17(18), 8323. https://doi.org/10.3390/su17188323

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