Adjustment of the marine ecological red lines in China

Abstract

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.

Introduction

Covering over 70% of the Earth’s surface, the ocean provides various ecosystem services such as supply, regulation, culture, and support, and is closely related to human well-being¹. Meanwhile, the ocean also bears the dual pressure of human activities and climate change². Marine ecological protection has become one of the common global concerns. Countries have taken measures to strengthen ecological protection and curb the trend of marine ecological deterioration, and the establishment of protected areas is a common in situ conservation measure adopted by all countries^3–6. The U.S. established the National System of Marine Protected Areas (MPAs), with nearly 1000 MPAs protecting 26% of the marine⁷. In the last 2 decades, the area of global MPAs has increased by more than 10 times, with 18,200 MPAs established globally, accounting for 7.74% of the global marine area⁸, while the number of large MPAs is growing rapidly⁹.To carry out ecological importance assessment has also become a common means to identify key areas for ecological conservation, such as ecological and biological significant areas (EBSAs)^10–12, key biodiversity areas (KBAs)^13,14, and important ecological areas (IEAs)¹⁵. The assessment indexes generally include aspects of uniqueness, degree of biological aggregation, naturalness, and resilience.

China’s marine ecosystem is facing similar dilemmas as that of the world, such as serious land-based pollution, reduction of biodiversity, decline of biological resources, and degradation of typical ecosystems^16,17. In 2012, China took the lead in the Bohai Sea to pilot the designation of marine ecological red lines (MERLs), which is an institutional innovation proposed by China under the guidance of systematic protection planning theory¹⁸, by designating protection scope and implementing special protection policies, to maximize the protection of ecological processes and functions in a specific area, so that limited financial, human and material resources can be optimally allocated¹⁹. The designation of China’s MERLs was completed in 2017, covering a total of 98,000 km², of which 15% was a prohibited-type red line, prohibiting all development and utilization activities, and 85% was a restricted-type red line, which restricts development and utilization activities that seriously affect the ecology, such as reclamation, dumping, and sewage discharge. The MERLs incorporates 30% of China’s offshore managed waters into the scope of protection, comprehensively takes into account the natural geographic pattern of the ocean and resource endowment characteristics²⁰, so as to realize the transformation from the management of individual and independent protected area to the management of comprehensive ecological zoning²¹. Through measures such as hierarchical control of red line areas²², marine ecological degradation caused by human activities has been curbed to a certain extent, and the anti-interference ability of marine ecologically fragile zones has been strengthened²³, initially constructed a marine ecological barrier for the protection of national ecological security and sustainable development.

There was no ecological importance assessment conducted before the designation of the original MERLs due to two reasons. First, there was no accurate survey data on the distribution of typical ecosystems at the time. Second, no unified and recognized assessment methodology had been established for judging and integrating the importance of various types of typical ecosystems, therefore, some ecologically important areas such as coral reefs and mangrove forests have not been included in the MERLs²³; the designation of the MERLs is later than the marine functional zoning (MFZ) that guides the use of marine space, and there is a lack of connection between the control requirements for the same marine space, which includes both the requirements for protection and the requirements for development and utilization²⁴. Due to the existence of insufficient protection space, the existence of human activities in the MERLs affecting the ecological functions, in 2019, based on the marine ecological importance assessment and the human activities disposal assessment, China carried out the adjustment of the MERLs, designated the areas of high ecological importance into the MERLs, and adjusted human activities area in the MERLs, incorporated MERLs into the “multiple planning integration” system. This method has significantly improved the effectiveness of the MERLs, and the results of the adjusted MERLs have been approved by the Chinese government and officially launched.

Methods

On the one hand, the adjustment of the MERLs is to incorporate as many ecologically important areas as possible into strict protection and to improve the scientific of the MERLs; on the other hand, it is to realistically solve the contradiction of human activities in the MERLs due to the policy change, and to improve the feasibility of the subsequent strict control of the MERLs. According to the purpose, the main methods for the adjustment include the following two, the marine ecological importance assessment and the human activities disposal assessment and the technical route is shown in Fig. 1.

Figure 1.

Roadmap for the adjustment of the marine ecological red lines (MERLs).

Methods for marine ecological importance assessment

Internationally, the main considerations for the marine ecological importance assessment include ecological service function and ecological vulnerability^13,15, combined with China’s current habitat degradation, biodiversity reduction, coastal erosion and other problems²⁵, as well as related research results in estuaries and other localized areas^26,27 to construct a technical method for marine ecological importance assessment (Fig. 2). China’s Marine ecological importance assessment technology and method system contains two aspects, namely, the importance of marine ecological service and marine ecological vulnerability. This paper suggests that two most important aspects of the marine ecological service are the marine biodiversity maintenance function and the coastal protection function, i.e., these two functions reflect the ability to maintain the stability and balance of the marine ecosystem, also the ability of providing suitable living conditions to other organisms, help resisting the impact of the external environment. Marine ecological vulnerability mainly includes coastal erosion and sand loss vulnerability, China’s natural coastline is less than 40%, at the same time, China’s coastal zone is already in the coastal erosion stage, China’s coastal areas will be faced with a long-term accelerated sea level rise, coastal erosion, storm surge threat increase in the natural geologic background²⁸, so the assessment of marine ecological vulnerability focused on the vulnerability of coastal erosion and sand loss. The assessment is carried out in a combination of qualitative and quantitative methods. Through the assessment, the high biodiversity maintenance function areas, the high coastal protection function areas and the high coastal erosion and sand loss vulnerability areas were assessed respectively, and the areas of high ecological importance were formed by maximizing integration method. This method has been officially released²⁹, and has been applied by Chinese scholars³⁰, and also in the Bay of Biscay in Europe³¹.

Figure 2.

Technical methods for marine ecological importance assessment.

Marine biodiversity maintenance function assessment

The marine biodiversity maintenance function assessment is conducted from three aspects: species diversity, ecosystem diversity, and genetic diversity (Table 1). Species diversity characterizes the richness and evenness of species and their relationship with the environment, and the targets of assessment are the species distribution area. Ecosystem diversity characterizes the diversity of the environment, biological communities, and ecological processes, and the targets of assessment are the typical ecosystems such as coral reefs, seagrass beds, estuaries, and coastal salt marshes. Genetic diversity characterizes the unique genes and genetic organization forms of species, and the targets of assessment are aquatic germplasm resource protection area and important fishery resource production and breeding area.

Table 1.

Marine biodiversity maintenance function assessment indicators.

Aspects	Types	Indicators	Grading criteria
			High ecological importance	Mid ecological importance
Species diversity	Species range	Population size	Endangered/critically endangered	Vulnerable
		Regional importance	Concentration area	Migratory zones
Ecosystem diversity	Coral reefs	Scale	Top 80% of scale	Bottom 20% of scale
	Mangroves	Scale	Top 80% of scale	Bottom 20% of scale
	Sea beds	Scale	Top 80% of scale	Bottom 20% of scale
	Coastal salt marshes	Scale	Top 50% of scale	Bottom 50% of scale
	Mudflats	Scale	Top 50% of scale	Bottom 50% of scale
		Regional Importance	A species of bird that exceeds 1% of its East Asian population
		Biological communities	Top 50% of macrobenthic species diversity	Bottom 50% of macrobenthic species diversity
	Estuaries	Scale	Top 50% of scale	Bottom 50% of scale
		Productivity	Chlorophyll concentration above 6 ug/L	Chlorophyll concentration below 6 ug/L
		Regional importance	A bird species that exceeds 1% of its East Asian population or is important in supporting the life history of a fishery resource such as migration	The rest estuaries
		Biological communities	Top 50% of spawning stock density	Bottom 50% of spawning stock density
	islands	Regional importance	A species of bird that exceeds 1% of its East Asian population	The rest islands
		Vegetation cover	Top 50% of vegetation cover	Bottom 50% of vegetation cover
		Importance of rights and interests	Islands in the territorial sea base point, islands in the territorial sea base point protection area	–
	Other endemic habitats such as oyster reefs, tidal sand ridges, etc	Uniqueness	High	–
Genetic diversity	Aquatic germplasm resource distribution area32	Regional importance	Aquatic Germplasm Resource Reserve Core Area	Aquatic germplasm resource reserve general area
	Fishery resources growth and breeding area	Regional importance	Spawning grounds	Important baiting grounds, wintering grounds, migratory corridors, etc
		Species importance	Keystone species	Common species

Coastal protection function assessment

The coastal protection function assessment is mainly conducted from two aspects: physical protection function and biological protection function. The assessment targets are bedrock coast, sandy coast, mangrove, and coastal salt marsh. Assessment indicators are shown in Table 2.

Table 2.

Coastal protection function assessment indicators.

Aspects	Types	Indicators	Grading criteria
			High ecological importance	Mid ecological importance
Physical protection	Bedrock coasts, sandy coasts	Coastal integrity	Top 50% of coast length	Bottom 50% of coast length
Biological protection	Mangroves, coastal salt marshes	Scale	Top 50% of scale	Bottom 50% of scale

Coastal erosion and sand loss vulnerability assessment

The coastal erosion and sand loss vulnerability assessment targets are coasts. Assessment indicators are shown in Table 3.

Table 3.

Coastal erosion and sand loss vulnerability assessment indicators.

Indicators		Grading criteria
		High ecological vulnerability	Mid ecological vulnerability
Geomorphology type		Silt coasts, Sandy coasts	Biological coasts
Storm surge maximum water gain		≥ 3.0 m	1.5–3.0 m
Mean wave height		≥ 1.0 m	0.4–1.0 m
Coastal erosion rate	Silt coasts	≥ 10 m/year	1–10 m/year
	Sandy coasts	≥ 2.0 m/year	0.5–2 m/year

Methods for human activities disposal assessment

Effective marine spatial planning (MSP) requires adequate understanding of the complexity of both biophysics and humans³³, and consideration of social-ecological linkages is necessary to evaluate trade-offs between social and ecological objectives³⁴. In the original MERLs, human activities other than dumping and reclamation were permitted, but in the adjusted MERLs, only eight limited categories of anthropogenic activities are permitted, such as aquaculture essential to the life of indigenous people, monitoring and investigation, conservation patrols, archaeology, moderate tourism, unavoidable linear infrastructure construction, exploration and exploitation of oil and gas resources, as well as ecological restoration. The policy in the adjusted MERLs is more stringent. So there are some human activities in the MERLs that are permitted by the original rules but will not be permitted by the current rules. In order to appropriately dispose human activities in the MERLs due to policy changes, it is necessary to carry out an human activities disposal assessment and categorize them according to the degree of authorized time and ecological effects³⁵. Disposal methods are categorized as adjusted out, retained and exit (Table 4).

Table 4.

Human activities disposal assessment methods in the MERLs.

Authorized time for human activities	Ecological effects	Activities types	Disposal
Activities authorized before the MERLs	Limited effects	Concentrated and large-scale open type aquaculture	Adjusted out of the MERLs
		Bathing beach use of the sea, tourism and recreation infrastructure use of the sea
		Salt use of the sea, industrial use of the sea, seawater comprehensive utilization of the sea
		Sea use for harbors, anchorages, and waterways requiring dredging
Activities authorized after the MERLs	Significant effects	Enclosed pond aquaculture	Exit from the MERLs
		Reclaimed land
		Mining of marine sand in ecologically important areas
Activities permitted in the MERLs		Open type aquaculture and less than 10% of the total area	Retained in the MERLs
		Point infrastructure such as power, water, communications, etc
		Ecotourism infrastructure that does not destroy ecological services
		Infrastructure for scientific investigation, monitoring, ecological restoration, etc
		Linear infrastructure such as cables, pipelines, cross-sea bridges, etc., which have already been rightsized

Data sources

In the marine ecological importance, data on the distribution areas of species are sourced from the Red List of China’s Biodiversity issued by the Ministry of Ecology and Environment of China³⁶. The data on coral reefs, seagrass beds, coastal salt marshes, coasts, mangroves, estuaries and islands are sourced from the Coastal Typical ecosystems Survey, the Third National Land Survey and the Special Comprehensive Survey and Evaluation of Offshore Marine organized by the Ministry of Natural Resources of China. The data on mudflats distribution are sourced from the Second National Wetland Resource Survey organized by the National Forestry and Grassland Administration. The data on estuaries distribution are sourced from the Second National Wetland Resources Survey organized by the State Forestry and Grassland Administration of China. The data of islands are sourced from the Monitoring of the Four Essential Factors of Uninhabited Islands organized by the China’s State Oceanic Administration. The distribution area of aquatic germplasm resources and the fishery resources growth and breeding areas are sourced from the Aquatic Germplasm Resource Reserve Bulletin issued by the Ministry of Agriculture of China. The data on coastal erosion, storm surge and wave height data are sourced from the annual marine observation and monitoring organized by the Ministry of Natural Resources of China.

The data on human activities in the MERLs are sourced from the marine development and utilization approval data of the Ministry of Natural Resources of China.

Results

Area and pattern

After adjustment, a total of approximately 85,000 km² of MERLs have been designated in China’s offshore zone, accounting for 26.6% of offshore zone, showing a distribution pattern of “one-belt and multi-point”. “One belt” covers the most important coastal wetlands in China, such as the Liao River estuary, Yellow River estuary, Yancheng City of Jiangsu Province, Yangtze River estuary, East Beach of Chongming Island, Hangzhou Gulf, Pearl River estuary, and almost all of the typical ecosystems of mangroves, coral reefs and seagrass beds, forming a ecological barrier distributed along the coastal zone. “Multi-point” covers most of the uninhabited islands, the distribution area of marine rare and endangered species, the habitat of migratory birds and spawning grounds of significant fishery resources, realizing the protection of key nodes such as biological habitat, breeding and migration (Fig. 3).

Figure 3.

Distribution of adjusted MERLs in offshore zone in China.

Among the eleven coastal provinces and cities in China, Hainan Province, Zhejiang Province, and Fujian Province have over 30% of MERLs, while Liaoning Province, Guangdong Province, Guangxi Province, Jiangsu Province, Shanghai, and Shandong Province have 20–30%. Among them, Guangdong Province, Zhejiang Province, Fujian Province, and Liaoning Province have more than 10,000 km² of MERLs (Fig. 4).

Figure 4.

Proportion of MERLs in 11 Coastal Provinces and Cities in China.

In terms of distribution characteristics, Liaoning Province is characterized by the concentrated distribution area of spotted seals and important estuaries such as the Liaohe estuary, the Yalu River estuary. Hebei Province is characterized by the largest seagrass bed ecosystem in China and bird migratory sites such as the Luannan Wetland. Tianjin Municipality is characterized by the ecosystems of oyster reefs and the foraging habitats of birds such as the Hangu Wetland. Shandong Province is characterized by the Yellow River estuary and the delta wetlands, seagrass beds, and long sandy coastal protection areas. Jiangsu Province is characterized by important mudflats and peripheral radial sand ridge groups, is a world natural heritage Yellow Sea and Bohai Sea migratory birds habitat. Shanghai Municipality is characterized by the Yangtze River estuary, the breeding and nursery areas of the Chinese mitten crab, the Yangtze River crabs. Zhejiang Province nearshore areas is characterized by bedrock coastal protection areas, Hangzhou Bay, Yueqing Bay, Nanji Islands and other island groups, etc., and the farshore areas is characterized by the spawning grounds of fishery resources. Fujian Province is characterized by Minjiang River estuary, the Jiulong River estuary, as well as the bays of Luoyuan Bay and Xinghua Bay. Guangdong Province is characterized by typical ecosystems such as mangrove forests, coral reefs and seagrass beds, important estuaries such as the Pearl River estuary, and the concentrated distribution areas of the Chinese white dolphin. Guangxi Zhuang Autonomous Region is characterized by the typical ecosystems of mangroves that are widely distributed in the nearshore areas, long sandy coastal protection areas, and the concentrated distribution areas of the Chinese white dolphin such as the Sanniang Gulf. Hainan Province is characterized by the typical ecosystems of coral reefs, mangroves, seagrass beds, and long sandy coastal protection areas.

Composition

In terms of the composition of the MERLs, 79% of the MERLs is the areas of high ecological importance, which is about 67,500 km², and 21% is the areas of mid ecological importance around them, which has a certain ecological service function or has potential ecological value. As a result of the marine ecological importance assessment, there are about 78,200 km² areas of high ecological importance in China’s offshore zone, of which approximately 69,800 km² areas were free of human activities, and 96.7% of the areas of high ecological importance were designated to the MERLs.

There are 11 types of MERLs, including mangroves, seagrass beds, coral reefs, coastal salt marshes, important estuaries, important mudflats and shallow waters, distribution areas of rare and endangered species, spawning grounds of fishery resources, specially in protected islands, the high coastal protection function areas, and the high coastal erosion and sand loss vulnerability areas (Fig. 5). The coastal zone is dominated by mangroves, seagrass beds, coral reefs, coastal salt marshes, important estuaries, important mudflats and shallow waters, while the offshore zone is dominated by spawning grounds of fishery resources, distribution areas of rare and endangered species, specially protected islands, etc.

Figure 5.

The types of MERLs.

Discussion

More reasonable types and distribution patterns of the MERLs

After the adjustment, the MERLs takes the areas of high ecological importance as the main body, and the division type is consistent with the direction of the marine ecological importance assessment, which contains eleven types in total. Compared with the original MERLs, there are newly added types such as important mudflats, high coastal protection function areas, high coastal erosion and sand loss vulnerability areas. While the types of “important coastal tourism areas”, “natural landscapes and historical and cultural relics” that are not directly related to the ecological service function importance and ecological vulnerability are took out. Also, the type of “marine protected areas” is took out since marine protected areas have clear conservation targets, such as specific species or typical ecosystems, and according to the results of the marine ecological importance assessment, the type of marine protected areas has been further differentiated into ecological types, such as mangroves or estuaries, but all marine protected areas have been fully integrated into the MERLs. Thus, the types of MERLs can more intuitively reflect the ecological service function importance and ecological vulnerability (Table 5). In terms of geographic distribution pattern, the adjusted MERLs increases the proportion of coastal regions, the important mudflats, high coastal protection function areas, high coastal erosion and sand loss vulnerability areas are all distributed in the coastal regions, thus effectively enhancing the protection intensity of the coastal regions, where the development and utilization activities are more intensive. The prohibited ratio of the original MERLs is about 5%, while after the adjustment, the protection proportion of the offshore zone in China increased to 26.6%. This ratio is in line with the goal of establishing 22% of marine priority conservation areas to achieve effective conservation of more than 95% of the species, genetic and phylogenetic diversity of marine animals³⁷, while the MERLs as a kind of Other Effective area-based Conservation Measures (OECMs), will have a positive effect on the promotion of the 30% targets for ocean protection in China as soon as possible.

Table 5.

Changes in types of MERLs before and after adjustment.

Types of the original MERLs	Types of the adjusted MERLs	Changes
Marine protected areas	–	The protected area as a whole is included in the MERLs and not classified as a single type, which is classified according to the dominant ecological function
Specially marine protected areas
Important estuarine ecosystems	Estuaries	Compared to the original MERLs, increase the high marine biodiversity areas, identify typical ecosystems with high ecological service functions, and expand the protection scope
Specially protected islands	Specially protected islands
Concentrated distribution areas of rare and endangered species	Concentrated distribution areas of rare and endangered species
Mangroves	Mangroves
Coral reefs	Coral reefs
Seagrass beds	Seagrass beds
Important fishing areas	Spawning grounds of fishery resources	Compared to the original MERLs, increase the importance assessment of the fishery resources growth and breeding areas, and designated spawning grounds of fishery resources in the MERLs, making the protection scope more scientific
Important coastal wetlands	Coastal salt marshes	The coastal wetlands are subdivided into two categories: coastal salt marshes and important mudflats and shallow waters, which are larger than the protection scope of the original MERLs
–	Important mudflats and shallow waters
Sandy coastline and adjacent waters	High coastal protection areas	Compared to the original MERLs, increase the assessment of the importance of coastal protection function and expand the protection scope
Sand source protected waters	High coastal erosion and sand loss vulnerability areas	Compared to the original MERLs, increase the high coastal erosion vulnerability areas and expand the protection scope
Important coastal tourism areas	–	The adjusted MERLs does not include these two types. Based on the background ecological importance, if an area has high ecological importance, it will be classified as the corresponding type
Natural landscapes and historical and cultural relics	–

Areas of high ecological importance in the MERLs increases

No importance assessment was conducted before the designation of the original MERLs. The adjusted MERLs is based on the results of the ecological importance assessment, and the areas of high ecological importance in the MERLs has significantly increased, for example, the proportion of the four typical ecosystems, namely, mangroves, seagrass beds, coral reefs and uninhabited islands, has increased from 68%, 77%, 76% and 51% to 98%, 89%, 88%, and 93%, respectively. These typical ecosystems are important strategic spaces in supporting marine ecological security. The strict protection by incorporating them into the MERLs not only helps to minimize the interference of human activities and ensure the various ecological service functioning, but also, is of great significance in consolidating blue carbon storage and enhancing the increment of blue carbon sinks, as carbon peak and carbon neutrality becomes an important framework for China’s medium to long term development. Against the backdrop of global threats to mangroves, the MERLs is key to ensure the effective protection of typical ecosystems such as mangroves, and has helped China become one of the few countries in the world with a net increase in mangrove areas³⁸.

Human activities intensity in the MERLs declines

The MERLs which coordinates existing and future human activities in the red line areas takes strict protection as its main goal, promotes the realization of the value of ecological products in itself, and seeks to optimize and adjust production, life, and ecological space from macro perspective³⁹.

There were 7400 km² of authorized human activities in the original MERLs, making it difficult to implement the management requirement of the prohibited development zone. After the adjustment, the human activities in the MERLs have dropped to 2400 km², and the intensity of human activities in the MERLs has decreased by 68%. From the perspective of sea use types in the MERLs, 90% are for fishery sea which have limited ecological effect. The remaining four types, industrial sea use, transportation sea use, submarine engineering sea use, and special sea use, account for about 2% each. Industrial sea use is mainly for oil and gas exploitation projects that remain in the MERLs. Against the backdrop of oil and gas resources being a national strategic security guarantee, legitimate oil and gas exploitation projects in MERLs are allowed to continue developing without expanding their scale and to exit in an orderly manner after expiration. The transportation sea use and submarine engineering sea use mainly include linear facilities such as waterways and submarine cables in the MERLs. Special sea use mainly includes scientific research, observation and monitoring, protection, and restoration. The normal implementation of these human activities has a relatively limited ecological impact of the MERLs. Overall, the adjustment of the MERLs has significantly reduced the intensity of human activities in the MERLs, and orderly resolved the contradictions between utilization and strict protection in specific spaces, clarifying the practical path of implementing mandatory protection requirements for the MERLs.

Unified use of marine space

MSP will aim at clarifying the overall distribution of protection and exploitation space, which is divided into two major parts: marine ecological space and marine exploitation space, of which the MERLs is the area with the highest ecological importance in the marine ecological space that needs to be strictly protected, and the marine ecological space outside the MERLs is mainly used to provide ecological product services. The marine exploitation space is divided into six functional zones according to the dominant function, oriented to intensive utilization of marine resources. While the MSP will replace the MFZ, and the adjusted MERLs will be implemented as a prioritized ecological bottom line in the MSP of the State, provinces and municipalities. Therefore, the current adjustment has solved the problem of the overlapping and non-connection between the original MERLs and the original MFZ. Taking Tianjin for example, the sea area is about 2146 km², and 220 km² of the original MERLs overlapped with the fishery areas, industrial and mining communications sea area, protected areas and coastal tourism areas of the MFZ. The dominant use is not uniform in 12% of the sea area (Fig. 6a). After the adjustment of the MERLs, the MERLs of Tianjin accounted for 12%, the marine ecological space accounted for 18%, the exploitation space accounted for 82% and have a gradient control (Fig. 6b).

Figure 6.

(a) The MFZ and the original MERLs in Tianjin. (b) The MSP and the adjusted MERLs in Tianjin.

Insufficient

In this paper, through the establishment of methods for marine ecological importance assessment and human activities disposal assessment, has carried out adjustment of the MERLs, which has improved the scientific nature of the results and the feasibility of the management to a certain extent, yet the assessment methods of the marine ecological importance still need to be perfected. With richer data from marine ecological surveys and more mature knowledge of the relationship between organisms and the environment, the indicators and grading standards for the assessment still need to be improved. At the same time, although the intensity of human activities in the MERLs declined after the adjustment, the areas that have been moved out of the MERLs because of human activities should continue to be paid attention to and evaluated, and recommendations on whether to designate to the MERLs should be made based on the conclusions of the ecological function and ecological vulnerability assessment.

Prospects

After the adjustment, the MERLs has been significantly optimized compared to the original MERLs in terms of type, distribution pattern, areas of high ecological importance proportion, human activities intensity, and spatial use. Further in-depth research is needed on the following aspects:

Firstly, strengthen the protection and restoration of the MERLs, and restore the ecologically important but damaged areas and ecologically fragile areas in the MERLs, to enhance the diversity, stability and sustainability of the ecosystems in the MERLs.

Secondly, strengthen the supervision of human activities in the MERLs, fully utilize multi-source data such as ship AIS and remote sensing images, to dynamically monitor and effectively control human activities intensity in it.

Thirdly, carry out monitoring and effectiveness assessment of MERLs, regularly assess the sea use structure, ecosystem quality, management situation, etc., link the assessment results with incentive mechanisms such as ecological protection compensation and central transfer payments for marine ecological restoration, guide and motivate governments to strengthen the protection and restoration in the MERLs, and orderly exit human activities from the MERLs.

Conclusion

Based on the assessment of the marine ecological importance and the human activities disposal, this paper has adjusted the original MERLs, and designated the MERLs for a total of 85,000 km² of offshore zone in China. The main goal of this study is to solve the problems of insufficient scientific assessment of the original MERLs and the lack of connection with the MFZ, to prioritize the protection of areas of high ecological importance, and to improve the science of the MERLs. The results show that the type and spatial layout of the MERLs better reflect the marine ecological characteristics, and the areas of high ecological importance in the MERLs increased, the contradiction between development and protection in the MERLs has been solved, the decision-making and deployment of the “multiple planning integration” effectively has been implemented, and a gradient pattern of marine spatial development and protection has been gradually formed.

Author contributions

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

Data availability

The original contributions presented in the study are included in the article, further inquiries can be directed to the corresponding author.

Competing interests

The authors declare no competing interests.