Multi-Objective Spatial Suitability Evaluations for Marine Spatial Planning Optimization in Dalian Coast, China

Abstract

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

1. Introduction

Ocean health is intrinsically linked to human well-being [1], and sustaining a healthy ocean is of great importance for the long-term viability of the blue economy [2,3]. However, rapid socio-economic development has intensified conflicts among various marine uses, with the demand for services and resources from sea and coastal areas frequently exceeding their capacities [4]. Moreover, the growth of marine activities has aggravated the degradation of natural habitats, loss of biodiversity and accumulation of contaminants, which, in turn, compromise the sustainable use of marine resources [5].

In this context, marine spatial planning (MSP) has emerged as an essential tool to address these challenges [6]. By analyzing and allocating the spatial and temporal distribution of human activities in marine areas, MSP can provide the balanced development of marine ecology, economy, and society [4]. Nevertheless, the increasing conflicts among diverse marine uses, together with the ongoing ecological degradation, underscore the urgent need for scientifically robust decision-support tools for managers. Hence, marine spatial suitability evaluation can play a pivotal role by integrating environmental, biophysical, and socio-economic factors to identify the most appropriate areas for specific activities, such as mariculture [7,8], wind energy farms [9], or urban development [10], among others. This evaluation process, typically carried out in the early stage of MSP, enables the identification of potential areas for future development and protection within a given sea area, while concurrently accounting for environmental sensitivity and resource availability, thereby contributing to the optimization of MSP schemes [11,12]. This step is also recognized as a key component of MSP by the European Union’s Maritime Spatial Planning Directive (Directive 2014/89/EU) [13] and by organizations such as IOC-UNESCO [14].

Despite its promising initial results, marine spatial suitability evaluation remains challenging. Previous studies have predominantly focused on single objectives, which have enhanced our understanding of the spatial distribution of specific marine activities, yet these efforts have contributed little to comprehensive spatial planning. Although recent research has increasingly sought to integrate disparate spatial suitability evaluations into unified planning frameworks [10,15,16], a consolidated framework specifically addressing marine spatial functional zoning remains absent. Given the diverse demands of stakeholders, ranging from development needs and ecological protection to prevailing socio-economic conditions, future research is essential on implementing multicriteria decision-making in MSP.

In this study, we propose an integrated analytical framework for multi-objective spatial suitability evaluation to optimize MSP schemes. The spatial suitability of key marine activities in the coastal waters of Dalian (China) was evaluated using a comprehensive indicator system, and the optimized MSP scheme was derived. Our approach incorporates the latest spatial management strategies in China and addresses multiple real-world demands by balancing ecological, economic, and social factors, thereby providing insights for the resolution of multi-use conflicts and the implementation of science-based MSP.

2. Study Area

This study was carried out in the coastal waters of Dalian, Liaoning Province, China, located between 38°43′ N and 40°10′ N and 120°58′ E to 123°31′ E in the Bohai Sea and the Yellow Sea, covering an area of approximately 29,000 km² (Figure 1). Dalian’s extensive coastline, exceeding 2200 km, and its more than 500 islands of varying sizes underscore the region’s rich marine resource endowment [17].

Dalian is one of the principal port cities in China, serving as a critical coastal hub whose marine economy substantially contributes to regional socio-economic development. Main marine activities include mariculture, fishing, shipping, port construction, and coastal tourism. Ecologically, the region is characterized by a mosaic of diverse ecosystems including coastal saltmarshes, seagrass meadows, and rocky, sandy, and muddy shorelines [18]. These ecosystems support a wide range of biodiversity and habitats but also function as vital migration corridors for birds along the Northeast Asian Flyway [19]. Moreover, the offshore waters provide essential spawning and feeding habitats for various fish species and serve as critical area for the nationally protected spotted seal (Phoca largha) [20,21].

However, the rapid industrialization and urbanization in Dalian have increasingly threatened the marine environment [22]. Issues such as marine pollution, wetland reduction, biodiversity loss, and coastal erosion have intensified [23,24]. Consequently, the intensification of conflicts among competing marine uses poses significant challenges to effective MSP and management (current distribution map of marine use see Figure 2). These challenges necessitate the development and implementation of robust, integrative planning strategies to ensure the sustainable utilization and conservation of marine resources.

3. Materials and Methods

3.1. Technical Framework

In this study, we propose an analytical framework to optimize MSP via multi-objective spatial suitability evaluation (Figure 3). The framework is structured around three principal components. First, we analyzed factors related to marine ecological protection and exploitation activities and identified relevant evaluation indicators to develop a hierarchical indicator system. Second, we conducted individual marine spatial suitability evaluations for each activity by collecting and processing indicator data, establishing suitability criteria and classification thresholds, and integrating the results to obtain comprehensive evaluations. Finally, we applied the multi-criteria decision analysis approach to synthesize the results and inform the optimization of the overall MSP process.

3.2. Indicator System Development

3.2.1. Marine Spatial Planning in China

China has been a global pioneer in MSP. Its efforts date back to the late 1970s [25,26]. The initial framework, Marine Functional Zoning (MFZ), served as the foundation of China’s MSP until 2020. Under MFZ, marine regions were classified into 8 primary and 22 secondary categories (

Table 1. Marine Functional Zoning and Territorial Spatial Planning system in China.

Category	Primary Type	Secondary Type
Marine Functional Zoning	1. Agriculture and Fishery Zone	1.1 Agricultural Reclamation Zone 1.2 Mariculture Zone 1.3 Proliferation Zone 1.4 Fishing Zone 1.5 Aquatic Genetic Resources Protection Zone 1.6 Fishery Infrastructure Zone
	2. Port and Shipping Zone	2.1 Port Zone 2.2 Channel Zone 2.3 Anchorage Zone
	3. Industrial and Urban Zone	3.1 Industrial Marine Zone 3.2 Urban Development Zone
	4. Mineral and Energy Zone	4.1 Oil and Gas Zone 4.2 Solid Mineral Zone 4.3 Salt Production Zone 4.4 Renewable Energy Zone
	5. Tourism and Entertainment Zone	5.1 Tourist Attraction Zone 5.2 Recreation Zone
	6. Marine Protected Zone	6.1 Marine Nature Reserve 6.2 Special Marine Protected Zone
	7. Special Use Zone	7.1 Military Zone 7.2 Other Designated Use Zone
	8. Reserved Zone	8.1 Reserved Zone
Territorial Spatial Planning	1. Marine Ecological Redline Zone	—
	2. Marine Ecological Control Zone	—
	3. Marine Exploitation Zone	2.1 Fishery Zone	Fishery Infrastructure Zone Mariculture and Proliferation Zone Fishing Zone
		2.2 Industrial, Mineral, and Communication Zone	Industrial Marine Zone Salt Production Zone Solid Mineral Zone Oil and Gas Zone Renewable Energy Zone Submarine Cable and Pipeline Zone
		2.3 Transportation Zone	Port Zone Shipping Zone Road, Bridge, and Channel Zone Airport Zone
		2.4 Entertainment Zone	Tourist Attraction Zone Recreation Zone
		2.5 Special Use Zone	Military Zone Scientific Research and Education Zone Marine Ecological Restoration and Shoreline Protection Engineering Zone Pollution Discharge and Dumping Zone Submarine Cultural Relics Preservation Zone
		2.6 Reserved Zone

) based on natural resource presence, geographical characteristics, and socio-economic attributes [27,28,29]. Although MFZ provided a robust basis for marine resource management, it had some limitations, especially the insufficient consideration of ecological protection and its narrow scope, which prevented the integration of land–sea management.

A major policy shift occurred in 2019, when the Chinese government approved the “multi-planning integration” strategy, with the Several Opinions on Establishing Territorial Spatial Planning System and Supervising Implementation [30,31]. This policy established a unified Territorial Spatial Planning System by merging previously separate planning frameworks (e.g., land-use planning, urban planning, and MFZ) into a single overarching framework. Within this new system, marine areas were reclassified into three distinct categories: Marine Ecological Redline Zone, Marine Ecological Control Zone, and Marine Exploitation Zone [32] (Table 1). The Marine Ecological Redline Zone designates areas under strict protection, while the Marine Ecological Control Zone aims to maintain ecosystem services and promote the development of ecological products [33]. This reclassification marks a significant shift from the previous MFZ framework by prioritizing ecological protection and securing adequate spatial allocation for ecological functions. In contrast, the Marine Exploitation Zone accommodates more intensive development activities, such as fisheries, port construction, shipping, and tourism. Notably, the updated framework also eliminates certain terrestrial-overlapping zones (e.g., Agricultural Reclamation Zone and Urban Development Zone), thereby improving land–sea spatial coordination.

In this study, we adopted the new Territorial Spatial Planning framework to optimize marine areas. Specifically, we considered four out of the six categories of Marine Exploitation Zone: Fishery Zone, Industrial, Mineral, and Communication Zone, Transportation Zone, and Entertainment Zone. The remaining two categories (Special Use Zone and Reserved Zone) were excluded, as they include sensitive military areas, scientific research facilities, marine ecological restoration projects, and submarine cultural relics with limited data availability. Moreover, the location of these areas is largely selected by policy and management decisions, making it difficult to conduct suitability evaluations. To streamline the research, we selected one representative activity for each category. Mariculture was chosen for the Fishery Zone, wind energy farm development for the Industrial, Mineral, and Communication Zone, port construction for the Transportation Zone, and coastal tourism for the Entertainment Zone. The selection of these specific activities was guided by several key considerations. First, they possess significant economic and ecological impacts, making them critical for understanding the dynamics of marine utilization. Second, comprehensive and reliable data were available, ensuring robust and sound analysis. Third, these activities align well with local development strategies in Dalian, thus enhancing the scientific validity of the study.

3.2.2. Indicator System

The indicators employed for the marine spatial suitability evaluation are summarized in Table 2.

The ecological protection evaluation is organized around three critical ecosystem services: biodiversity maintenance, coastal protection, and carbon sequestration. Criteria for biodiversity maintenance were derived from internationally recognized frameworks, including Key Biodiversity Areas (KBAs) and Ecologically or Biologically Significant Marine Areas (EBSAs) [34,35]. Indicators for coastal protection and carbon sequestration were adapted to Dalian’s coastal ecosystems from previous studies [36,37].

Marine exploitation suitability was evaluated using supporting resources, environmental constraints, and socio-economic constraints. Specifically, mariculture suitability was evaluated focusing on the bottom-sowing method, which constitutes approximately 75% of Dalian’s annual production, and used phytoplankton abundance and substrate type as supporting resource indicators, water quality and disaster risks as environmental constraint indicators [38,39,40]. Port construction suitability was evaluated based on four primary factors of shorelines: substrate type, slope, water depth, and storm surge risk [41,42,43]. Wind energy farm development suitability was evaluated using wind energy density measured at 100 m elevation, with water depth and sea ice risk as the main environmental constraints [44,45,46,47]. According to China’s Offshore Wind Energy Development and Construction Regulations, offshore wind installations must be located at least 10 km offshore [48]. Finally, coastal tourism suitability was determined based on the availability of shoreline resources and high-value tourist attractions, with additional consideration of environmental factors including water quality and red tide risk [41,49].

3.2.3. Individual Marine Spatial Suitability Evaluation

The developed indicator system was operationalized through the compilation of a comprehensive spatial dataset that integrates information from multiple sources, including national monitoring and survey programs (e.g., National Coastal Ecosystem Survey, National Land Survey, National Marine Disaster Risk Census, National Ecological Warning and Monitoring Project), open-access marine data platforms (e.g., National Marine Big Data Service), and peer-reviewed reports (Bulletin of China Marine Disasters) and literature.

Table 2. Data sources for marine spatial suitability evaluation.

Goal	Criteria	Indicator for Dalian Waters	Data Source	Suitability Evaluation
				Suitable	Moderately Suitable	Unsuitable
Marine ecological protection	Habitats of key protected or threatened species	—	[19,21,50]	Habitats of rare and endangered seabirds	—	Other sea areas
	Habitats with high biodiversity or productivity	Seagrass meadows, tidal flats, estuaries, uninhabited sea islands	National Coastal Ecosystem Survey (2021), Second National Wetland Survey (2014), National Uninhabited Sea Island Survey (2016)	Seagrass meadows; tidal flats with the bird population exceeding 1% of East Asian population, or with a cumulative percentage of area over 50%; estuaries with chlorophyll concentration > 6 μg L−1; uninhabited sea islands with vegetation coverage > 50%	Other tidal flats, estuaries, and unutilized uninhabited sea islands	Other sea areas
	Critical habitats supporting key life-history stages of species	Fishery spawning, feeding, wintering grounds, and migration areas, aquatic germplasm resource protected areas	Ministry of Agriculture, 2002; Notification of the Ministry of Agriculture and Rural Affairs (https://www.moa.gov.cn (accessed on 2 January 2025))	Fishery spawning grounds, aquatic germplasm resources protection areas	Fishery wintering, feeding and migration areas	Other sea areas
	Habitats offering coastal protection service	Rocky, sandy, muddy shorelines	National Coastal Ecosystem Survey (2021), National Sea Area Dynamic Monitoring System	Natural shorelines > 500 m and no utilization by the seaward side	Natural shorelines > 500 m	Other sea areas
	Habitats offering carbon sequestration service	Coastal saltmarshes, seagrass meadows	National Coastal Ecosystem Survey (2021)	Coastal saltmarshes (invasive species communities excluded), seagrass meadows	—	Other sea areas
Mariculture	Supporting resources	Phytoplankton abundance	National Ecological Warning and Monitoring project (2006–2023)	≥1.0 × 107 cells m−3	<1.0 × 107 cells m−3	—
		Substrate type	Global ocean sediment product (https://oceancloud.nmdis.org.cn (accessed on 2 January 2025)) [51]	Sand or silt	—	Gravel
	Environmental constraints	Seawater quality	National Ecological Warning and Monitoring project (2006–2023)	First- or second-class seawater quality	—	Other classes
		Red tide risk	Bulletin of China Marine Disasters (https://www.mnr.gov.cn/sj/sjfw/hy/gbgg/zghyzhgb/index_1.html (accessed on 2 January 2025))	Numbers of red tide records < 3	Numbers of red tide records ≥ 3	—
		Sea ice risk		Numbers of sea ice records < 6	Numbers of sea ice records ≥ 6	—
Port construction	Supporting resources	Slope (average slope within 2 km buffer zone)	90 m resolution Digital Elevation Model (DEM) data of Chinese coastal areas (2020)	≤8°	8–15°	>15°
		Shoreline substrate type	Third National Land Survey (2020)	Artificial shoreline, rocky shoreline	Muddy shoreline	Sandy, biogenic shoreline
		Water depth (Distance to 10 m depth contour)	Global bathymetry grid product (https://oceancloud.nmdis.org.cn/ (accessed on 2 January 2025))	<10 km	10–15 km	≥15 km
	Environmental constraint	Storm surge risk	National Marine Disaster Risk Census	Other classes	Fourth class	—
Wind energy farm development	Supporting resources	Wind energy density	China Meteorological Administration	≥500 W m−2	350–500 W m−2	<350 W m−2
	Environmental constraints	Water depth	global bathymetry grid product (https://oceancloud.nmdis.org.cn/ (accessed on 2 January 2025))	≤50 m	>50 m	—
		Sea ice risk	Bulletin of China Marine Disasters (https://www.mnr.gov.cn/sj/sjfw/hy/gbgg/zghyzhgb/index_1.html (accessed on 2 January 2025))	Numbers of sea ice records < 6	Numbers of sea ice records ≥ 6	—
	Socio-economic constraint	Distance to shoreline	Third National Land Survey (2020)	≤10 km	—	>10 km
Coastal tourism	Supporting resources	Tourism resource	Third National Land Survey (2020), Points of Interest (POI) on Baidu Map (https://map.baidu.com (accessed on 2 January 2025))	Biogenic/sandy/rocky shoreline; AAAAA, AAAA, and AAA National Tourist Attractions; National Marine Park	Muddy shoreline; other tourist attractions; other parks	Artificial shoreline
	Environmental constraint	Seawater quality	National Ecological Warning and Monitoring (2006–2023)	First- or second-class seawater quality	—	Other classes
		Red tide risk	Bulletin of China Marine Disasters (https://www.mnr.gov.cn/sj/sjfw/hy/gbgg/zghyzhgb/index_1.html (accessed on 2 January 2025))	Numbers of red tide records < 3	Numbers of red tide records ≥ 3	—

Table 2. Data sources for marine spatial suitability evaluation.

Goal	Criteria	Indicator for Dalian Waters	Data Source	Suitability Evaluation
				Suitable	Moderately Suitable	Unsuitable
Marine ecological protection	Habitats of key protected or threatened species	—	[19,21,50]	Habitats of rare and endangered seabirds	—	Other sea areas
	Habitats with high biodiversity or productivity	Seagrass meadows, tidal flats, estuaries, uninhabited sea islands	National Coastal Ecosystem Survey (2021), Second National Wetland Survey (2014), National Uninhabited Sea Island Survey (2016)	Seagrass meadows; tidal flats with the bird population exceeding 1% of East Asian population, or with a cumulative percentage of area over 50%; estuaries with chlorophyll concentration > 6 μg L−1; uninhabited sea islands with vegetation coverage > 50%	Other tidal flats, estuaries, and unutilized uninhabited sea islands	Other sea areas
	Critical habitats supporting key life-history stages of species	Fishery spawning, feeding, wintering grounds, and migration areas, aquatic germplasm resource protected areas	Ministry of Agriculture, 2002; Notification of the Ministry of Agriculture and Rural Affairs (https://www.moa.gov.cn (accessed on 2 January 2025))	Fishery spawning grounds, aquatic germplasm resources protection areas	Fishery wintering, feeding and migration areas	Other sea areas
	Habitats offering coastal protection service	Rocky, sandy, muddy shorelines	National Coastal Ecosystem Survey (2021), National Sea Area Dynamic Monitoring System	Natural shorelines > 500 m and no utilization by the seaward side	Natural shorelines > 500 m	Other sea areas
	Habitats offering carbon sequestration service	Coastal saltmarshes, seagrass meadows	National Coastal Ecosystem Survey (2021)	Coastal saltmarshes (invasive species communities excluded), seagrass meadows	—	Other sea areas
Mariculture	Supporting resources	Phytoplankton abundance	National Ecological Warning and Monitoring project (2006–2023)	≥1.0 × 107 cells m−3	<1.0 × 107 cells m−3	—
		Substrate type	Global ocean sediment product (https://oceancloud.nmdis.org.cn (accessed on 2 January 2025)) [51]	Sand or silt	—	Gravel
	Environmental constraints	Seawater quality	National Ecological Warning and Monitoring project (2006–2023)	First- or second-class seawater quality	—	Other classes
		Red tide risk	Bulletin of China Marine Disasters (https://www.mnr.gov.cn/sj/sjfw/hy/gbgg/zghyzhgb/index_1.html (accessed on 2 January 2025))	Numbers of red tide records < 3	Numbers of red tide records ≥ 3	—
		Sea ice risk		Numbers of sea ice records < 6	Numbers of sea ice records ≥ 6	—
Port construction	Supporting resources	Slope (average slope within 2 km buffer zone)	90 m resolution Digital Elevation Model (DEM) data of Chinese coastal areas (2020)	≤8°	8–15°	>15°
		Shoreline substrate type	Third National Land Survey (2020)	Artificial shoreline, rocky shoreline	Muddy shoreline	Sandy, biogenic shoreline
		Water depth (Distance to 10 m depth contour)	Global bathymetry grid product (https://oceancloud.nmdis.org.cn/ (accessed on 2 January 2025))	<10 km	10–15 km	≥15 km
	Environmental constraint	Storm surge risk	National Marine Disaster Risk Census	Other classes	Fourth class	—
Wind energy farm development	Supporting resources	Wind energy density	China Meteorological Administration	≥500 W m−2	350–500 W m−2	<350 W m−2
	Environmental constraints	Water depth	global bathymetry grid product (https://oceancloud.nmdis.org.cn/ (accessed on 2 January 2025))	≤50 m	>50 m	—
		Sea ice risk	Bulletin of China Marine Disasters (https://www.mnr.gov.cn/sj/sjfw/hy/gbgg/zghyzhgb/index_1.html (accessed on 2 January 2025))	Numbers of sea ice records < 6	Numbers of sea ice records ≥ 6	—
	Socio-economic constraint	Distance to shoreline	Third National Land Survey (2020)	≤10 km	—	>10 km
Coastal tourism	Supporting resources	Tourism resource	Third National Land Survey (2020), Points of Interest (POI) on Baidu Map (https://map.baidu.com (accessed on 2 January 2025))	Biogenic/sandy/rocky shoreline; AAAAA, AAAA, and AAA National Tourist Attractions; National Marine Park	Muddy shoreline; other tourist attractions; other parks	Artificial shoreline
	Environmental constraint	Seawater quality	National Ecological Warning and Monitoring (2006–2023)	First- or second-class seawater quality	—	Other classes
		Red tide risk	Bulletin of China Marine Disasters (https://www.mnr.gov.cn/sj/sjfw/hy/gbgg/zghyzhgb/index_1.html (accessed on 2 January 2025))	Numbers of red tide records < 3	Numbers of red tide records ≥ 3	—

Each evaluation indicator was then classified into three levels (suitable, moderately suitable, and unsuitable) and standardized to a common scale (2, 1, and 0, respectively). This classification was based on four key criteria:

(i).

Policy compliance, related to China’s ecological protection targets, following the methodologies proposed by Zeng et al. [32];

(ii).

Regulatory standards, based on national technical specifications such as China’s Water Quality Standard for Fisheries (GB 11607-89) [52], the Methodology of Wind Energy Resource Assessment for Wind Farm (GB/T 18710-2002) [53], and the Technical Directives for Risk Assessment and Zoning of Marine Disaster Part I: Storm Surge (HY/T 0273-2019) [54];

(iii).

Technical requirements, which account for physical constraints specific to certain activities, e.g., sandy or silty substrates for bottom-sowing aquaculture, artificial or rocky shorelines for port construction, and water depth less than 50 m for wind energy farms [45,47];

(iv).

Local adaptation, which employs the Jenks Natural Breaks classification to capture region-specific variations in phytoplankton abundance, disaster risk indicators, and tourism resource metrics [55,56].

Finally, the individual indicator scores were synthesized using the extremum method. The maximum method was employed with equal weights for all the ecological protection indicators to delineate the broadest possible ecological zone. The minimum method was used for evaluating the exploitation activities, to ensure that high-risk environmental constraints are prioritized.

3.3. Marine Spatial Planning Optimization

Building on the spatial suitability evaluations for the five key marine activities, we employed a multicriteria decision analysis approach to integrate these suitability outcomes with existing spatial utilization patterns. The primary objective was to optimize the MSP scheme by balancing ecological protection and sustainable exploitation.

The process began with creating a comprehensive spatial data layer that merged the suitability results for all functions into a vector-based mosaic. Each spatial unit’s suitability score then informed functional allocation through a hierarchical decision-making protocol:

• Ecological priority. Spatial units scoring the maximum for ecological protection (score = 2) were designated as Ecological Redline Zones. Low-intensity development areas with limited ecological impact were also included, while high-intensity zones adversely affecting ecological functions were excluded.
• Stable development. Areas currently supporting large-scale exploitation activities with a suitability score ≥1 retained their existing designations to preserve planning continuity and minimize socio-economic disturbances.
• Protection-development coordination. For remaining spatial units, final designations were determined by considering: (i) protection priority for undeveloped areas; (ii) optimization based on the highest suitability score; and (iii) consideration of adjacent exploitation functions using the visual interpretation method to ensure spatial coherence. Notably, for port construction, which is evaluated along the shoreline, a 5 km seaward buffer from the suitable coastline was used as the Port Zone boundary, reflecting the typical spatial extent of port activities in Dalian’s coastal waters.

4. Results

4.1. Individual Suitability Evaluation Results

The spatial suitability of the five distinct marine functions described above was evaluated, and the results for all individual indicators and comprehensive suitability are presented in Figure 4 and Figure 5 and

Table 3. Spatial suitability results in the coastal waters of Dalian, China.

Goal	Criteria/Indicator	Suitable (%)	Moderately Suitable (%)	Unsuitable (%)
Ecological protection	habitats of key protected or threatened species	14.3	0.0	85.7
	habitats with high biodiversity or productivity	2.1	11.4	86.5
	critical habitats supporting key life-history stages of species	7.1	45.6	47.3
	habitats offering coastal protection service	0.8	0.0	99.2
	habitats offering carbon sequestration service	0.0	0.0	100.0
	Integrated result	22.8	55.4	21.8
Mariculture	Phytoplankton abundance	43.0	57.0	0.0
	Substrate type	99.4	0.0	0.6
	Water quality	97.9	0.0	2.1
	Red tide risk	99.7	0.3	0.0
	Sea ice risk	85.2	14.8	0.0
	Integrated result	32.3	65.0	2.7
Wind energy farm development	Wind energy density	70.4	25.7	3.9
	Water depth	55.0	45.0	0.0
	Distance to shoreline	80.1	0.0	19.9
	Sea ice risk	85.2	14.8	0.0
	Integrated result	20.7	59.4	19.9
Port construction	Substrate type	91.5	1.1	7.4
	Slope	91.1	8.4	0.5
	Water depth	34.7	19.8	45.4
	Storm surge risk	84.4	15.6	0
	Integrated result	15.8	32.6	51.6
Coastal tourism	Tourism resources	0.2	1.3	98.5
	Water quality	97.9	0.0	2.1
	Red tide risk	99.7	0.3	0.0
	Integrated result	0.7	1.2	98.1

. The results showed significant differences among the five marine functions. Mariculture exhibited extensive spatial applicability, with suitable and moderately suitable areas accounting for as much as 97.3% of the coastal waters of Dalian, China. In contrast, coastal tourism displayed marked spatial constraints and limited resources, with suitable and moderately suitable areas covering only 1.9% of the study area.

4.2. Marine Spatial Planning Scheme Optimization Result

Figure 6a provides a comprehensive overview of the spatial suitability evaluation results for five distinct activities in the coastal waters of Dalian. In this analysis, the suitability index represents the cumulative sum of the individual suitability scores, with higher values indicating the suitability of an area for a higher number of activities. These areas support both exploitation activities and ecological protection, highlighting the intricate connections and dependencies between development and protection priorities.

Furthermore, a multicriteria decision analysis approach was employed incorporating the status of regional development and utilization, to delineate an MSP scheme for Dalian’s coastal waters (Figure 6b and

Table 4. Marine spatial planning scheme in the coastal waters of Dalian, China.

Primary Type	Secondary Type	Area Proportion (%)
Marine Ecological Redline Zone		22.0
Marine Ecological Control Zone		32.4
Marine Exploitation Zone	Fishery Zone	39.7
	Wind Energy Zone	3.0
	Port Zone	2.6
	Recreation Zone	0.3

). According to the proposed scheme, Ecological Redline Zones and Ecological Control Zones comprise 22.0% and 32.4% of the marine area, respectively. Both offshore and coastal regions are included within these zones. Offshore areas are predominantly reserved for ecologically dominant functions, such as habitats of key protected species and fisheries resources, while coastal areas have been reconfigured to minimize high-intensity development conflicts and preserve critical estuaries, wetlands, and island-adjacent waters. As a result, some coastal zones have been reclassified to accommodate specific development purposes, including port and fisheries use. Notably, within the Marine Exploitation Zones, fisheries activities occupy a dominant position, covering 39.7% of the total area, while other development uses are largely concentrated along the coastline.

5. Discussion

5.1. Spatial Differentiation of Multiple Suitability Evaluations

The spatial suitability evaluation reveals pronounced heterogeneity in Dalian’s coastal waters. Notably, areas classified as “suitable” for marine ecological protection predominantly include habitats for key protected or threatened species (62.6%) and critical habitats supporting key life-history stages (30.9%). In fact, the western Bohai Sea, adjacent to the Dalian coast, serves as a crucial habitat for Phoca largha, a national first-class key protected species, and acts as an ecological corridor linking the northern breeding grounds in Liaodong Bay with the summering grounds in the northern Yellow Sea [21,57]. Furthermore, islands such as Huping, Shedao, and Haimao provide vital refuges for species like Gloydius shedaoensis (a national second-level key protected species, listed as Vulnerable on the International Union for Conservation of Nature Red List), as well as for several migratory birds including Egretta eulophotes, Aquila clanga, Platalea minor, Ciconia boyciana, and Aythya baeri. These migratory species, designated as national first-level key protected species, exhibit diverse conservation statuses, ranging from Vulnerable to Critically Endangered [19,58,59]. In addition, the southern Bohai Strait, which forms a transition zone between the Bohai and Yellow Seas, largely contributes to ecological connectivity by serving as a significant corridor for fishery resources during key biological processes, while major estuaries and coastal wetlands in the region provide essential breeding and stopover sites for a variety of waterbirds.

Regarding marine exploitation, the evaluation indicates substantial spatial feasibility for mariculture, primarily driven by favorable substrate conditions (99.4%) and relatively abundant phytoplankton (43.0%), both of which indicate strong environmental support and high potential for biological productivity. The most favorable mariculture zones are primarily located in the eastern waters of the Yellow Sea, with the remaining areas generally falling within the “moderately suitable” category. Wind energy potential is similarly promising, as high wind energy density (70.4%) largely dictates the spatial layout of suitable areas, although proximity to the shoreline imposes certain limitations. The optimal sites for wind energy are identified in the offshore waters of the Bohai Sea and the central Yellow Sea. In contrast, port construction faces significant constraints, chiefly due to insufficient water depth (45.4%). Along the Bohai Sea coast, irregular shorelines, such as those at Taiping Bay, Hulushan Bay, and Lvshunkou, demonstrate relatively higher suitability, whereas the straighter coastlines of the Yellow Sea tend to concentrate suitable areas around islands like the Changshan Archipelago and Shicheng Island. Lastly, although the areas deemed “suitable” and “moderately suitable” for coastal tourism account for less than 1% of Dalian’s waters, the overall tourism potential is relatively widespread and is minimally affected by factors such as water quality or red tide occurrences.

5.2. Weighting the Suitability Evaluation

As described in Section 3.3, the integration of individual indicators employed equal weights and the extremum method to generate the comprehensive suitability result. However, given that many studies advocate for assigning distinct weights to each indicator [8,60], we subsequently reconducted the suitability evaluation using weighted indicators. This allowed comparing outcomes and assessing the advantages and limitations of both methods.

For ecological protection, we adopted the methodologies proposed by Korpinen et al. [61] and Borja et al. [60], while for exploitation activities, we followed the approaches of Wei et al. [10] and Dong et al. [62] (consult weight coefficients in

Table 5. Weights of each indicator for the analysis of spatial suitability.

Goal	Criteria	Indicator	Weight
Marine ecological protection	Habitats of key protected or threatened species	Habitats of Spotted Seal	2.227
		Habitats of rare and endangered seabirds	2.367
	Habitats with high biodiversity or productivity	Seagrass meadows	2.873
		Tidal flats	2.807
		Estuaries	2.553
		Uninhabited sea islands	2.147
	Critical habitats supporting key life-history stages of species	Fishery spawning feedings, wintering grounds, and migration areas, aquatic germplasm resource protected areas	3.273
	Habitats offering coastal protection service	Rocky shorelines	2.800
		Sandy shorelines	2.520
		Muddy shorelines	2.533
	Habitats offering carbon sequestration service	Coastal saltmarshes	2.570
		seagrass meadows (already listed in “Habitats with high biodiversity or productivity”, and excluded from calculation)	—
Mariculture	Supporting resources (guiding)	Phytoplankton abundance	0.143
		Substrate type	0.857
	Environmental constraints (constraint)	Seawater quality	—
		Red tide risk	—
		Sea ice risk	—
Port construction	Supporting resources (guiding)	Slope	0.078
		Shoreline substrate type	0.171
		Water depth	0.750
	Environmental constraint (constraint)	Storm surge risk	—
Wind energy farm development	Supporting resources (guiding)	Wind energy density	1
	Environmental constrain (constraint)	Water depth	—
		Sea ice risk	—
	Socio-economic constraint (constraint)	Distance to shoreline	—
Coastal tourism	Supporting resources (guiding)	Tourism resource	1
	Environmental constraint (constraint)	Seawater quality	—
		Red tide risk	—

). Notably, in the evaluations of wind energy farm development and coastal tourism, only one guidance indicator (assigned a weight of 1) was used, yielding results identical to those obtained using the extremum method. Compared with this method, the weighted method increased the area classified as ecologically “suitable” from 22.8% to 66.9% (Figure 7a), with additional suitable areas primarily located in the Bohai Strait and central Dalian Yellow Sea, which support critical life history stages of species. Conversely, key nearshore estuaries and tidal wetlands experienced a decrease in suitability. These shifts closely reflect the weight coefficients, which are based on the sensitivity of each ecosystem to human pressures. Although the weighting method effectively captures the ecological risks and precautionary principles for each indicator [60], it deviates somewhat from typical protection patterns. Nearshore waters, with higher biodiversity and human activity, generally require stronger protection, whereas offshore spawning grounds, despite their ecological significance, are subjected to fewer pressures and thus are often assigned lower priority. In terms of marine exploitation, the weighted evaluation for mariculture identified a “suitable” area of 33.1%, compared to 32.3% with the extremum method, although the “unsuitable” area increased from 2.7% to 17.2% (see Figure 7b). For port construction, the weighting method expanded the “suitable” area from 15.8% to 37.3% and reduced the “unsuitable” area from 51.6% to 22.9% (see Figure 7c). These discrepancies primarily stem from the redistribution of indicator importance and the variability introduced by the statistical thresholding methods.

Overall, the selection of the extremum method has a significant impact on the final suitability evaluation results. The weighting method provides a more nuanced representation of individual indicator influences and better reflects ecological sensitivities, but it introduces additional variability and depends critically on the assumptions used in weight assignment and threshold classification. In contrast, the extremum method, while simpler and more predictable, may overlook important differences in indicator importance. Future research should therefore appropriately integrate weighting and sensitivity analysis methods while ensuring robust analytical results, thereby striking a balance between scientific rigor and practical feasibility.

5.3. Analysis of the Spatial Planning Scheme Optimization

Over the past three decades, MSP has experienced rapid development, but reconciling development with protection remains a core challenge [63,64,65]. In recent years, the Chinese government has prioritized ecological considerations in marine spatial allocations [33]. Accordingly, our optimized planning scheme identifies 22.0% of the marine area as Ecological Redline Zones and 32.4% as Ecological Control Zones. This allocation effectively preserves core ecosystem services by encompassing most areas identified as ecological “suitable” (22.8%) and “moderately suitable” (55.4%). Furthermore, integrating suitability evaluations with existing spatial patterns in multi-use areas has facilitated stakeholder negotiations, a crucial factor given the high economic stakes and diverse interests in marine spaces [10,64]. Consequently, the proposed scheme retains development functions in over 90% of current utilization zones while ensuring that each functional area aligns with its respective suitability classification and environmental protection objectives.

Currently, the spatial development suitability evaluations have already been institutionalized as an important component of territorial spatial planning [15,31,33]. Nonetheless, MSP is inherently a multi-stakeholder, continuously negotiated process, and our approach has several limitations: (i) categorizing suitability into three broad categories (suitable, moderately suitable, and unsuitable), although practical for planning, may oversimplify spatial heterogeneity; and (ii) the optimization process is closely aligned with current policies and utilization patterns, which may limit its applicability under future scenarios that demand dynamic integration of social and ecological resilience [9,66]. Future work could address these limitations by refining the suitability classification (e.g., using continuous suitability scores or additional categorical levels) and incorporating scenario-based analyses to improve the adaptability of the optimization process.

6. Conclusions

This study proposed a science-based and policy-aligned framework for implementing MSP in Dalian’s coastal waters. By addressing the spatial requirements of multiple marine activities, the framework facilitates identification of areas suitable for both ecological protection and sustainable development, enabling a comprehensive evaluation of spatial heterogeneity, functional trade-offs, and synergies. The resulting zoning scheme, comprising Ecological Redline Zones, Ecological Control Zones, and Marine Exploitation Zones, reflects both ecological value and socio-economic needs, aligning spatial management strategies with regional resource availability, environmental capacity and current use patterns. While the proposed framework provides a valuable foundation for data-driven informed MSP, its long-term effectiveness relies on the continuous refinement of ecological and socio-economic datasets, as well as the integration of predictive modeling to anticipate future ecological and anthropogenic changes. Future research should aim to further integrate systematic planning and artificial intelligence with comprehensive ecological and socio-economic datasets to enable adaptive, forward-looking MSP. Overall, this study contributes a replicable, science-based approach to MSP and offers strategic insights for implementation in coastal regions facing competing development and conservation demands.