Reflections on How to Reach the “30 by 30” Target: Identification of and Suggestions on Global Priority Marine Areas for Protection

Abstract

The establishment of marine protected areas (MPAs) is an important method to ensure marine protection. To protect and conserve global marine biodiversity, with the adoption of the “Kunming-Montreal Global Biodiversity Framework” during the 15th meeting of the Conference of the Parties of Convention on Biodiversity (CBD) in December 2022, the establishment of an effectively managed MPA network by 2030 and the protection of 30% of the world’s oceans will be common goals for all countries party to the CBD over the next decade. Based on the distribution of over 150 types of marine species, habitats, ecosystems, and abiotic elements, ArcGIS10.5 and Zonation are used in this study to calculate the marine protection priority levels of coastal, nearshore, open ocean, and deep ocean trench areas, and a plan to reach the “30 by 30” targets is proposed. The suggestions for scientifically identifying and managing MPAs are as follows: first, improve MPA planning and establish a well-connected MPA network in national jurisdictions, then conduct scientific marine investigations to obtain background data on MPA establishment and delimitation.

1. Introduction

The ocean is the foundation of all life, providing us with space for transportation, trade, and recreation [1]; cultural heritage [2]; and resources, including food [3], drugs [4], and minerals [5]. Meanwhile, the ocean is also the largest carbon reservoir in the Earth system [6], with approximately a quarter of anthropogenic carbon dioxide emissions being absorbed by oceans over the last two decades [7]. With the rapid increases in the human population and material demands, the scope of human utilization of the ocean has expanded from coastal regions [8] to the high seas [9] and international seabeds [10]. Over-exploitation and harvesting, land-based pollution, and marine invasion have created great losses of marine life [8]. Moreover, oceangoing activities such as biological resource surveys and deep-sea mineral exploration and exploitation pose a serious threat to areas beyond national jurisdictions. Establishing marine protected areas (MPAs) is an effective way to systematically address marine environmental problems and resolve the crisis of biodiversity destruction [11,12]. Considering the synergistic effects of marine connectivity, fluidity and population growth, climate change, and other stressors, there is a need to identify and establish MPAs on a global scale. In December 2022, the second phase of the 15th Conference of the Parties (COP) on the Convention on Biological Diversity (CBD) adopted the “Kunming-Montreal Global Biodiversity Framework”, which sets a highly ambitious global marine conservation target for the next decade, aiming to “reverse and halt global biodiversity loss and enhance biodiversity and ecosystem functions and services, ecological integrity and connectivity through area-based conservation measures to protect at least 30 percent of global coastal and marine areas by 2030” [13], referred to as the so-called “30 by 30” target. There is a global consensus to designate marine protected areas and protect marine biodiversity in the coming decade.

Since the 10th COP of the CBD in 2010, which set the target of protecting 10% of the world’s oceans and seas by 2020, the pace of MPA expansion and new designations has accelerated [14]. However, the science behind new MPA designations and effectiveness needs to be strengthened [15]. By August 2023, a total of 29.59 million square kilometers of MPAs of all types and levels had been established globally, accounting for 8.17% of the global marine area, of which 18.7% was protected in marine areas under national jurisdiction and 1.44% in marine areas beyond national jurisdiction, falling short of the 10% protection target [16,17]. There is also a general lack of scientifically informed and effective management plans and feasible management measures for MPAs, insufficient attention to ecosystem representation and connectivity, and low effectiveness of actual protection efforts [15]. Biodiversity loss has not been effectively mitigated, and the security of critical habitats is still threatened [18,19]. According to the International Union for Conservation of Nature (IUCN), 5510 threatened species (21% of all threatened species) are covered by biodiversity-critical areas globally, of which 13% are entirely within protected areas, while another 31% are only partially covered by marine protected areas [15]. The appropriateness and effectiveness of selecting MPAs already in place must be further explored.

In accordance with current international law, all MPAs established under the United Nations Convention on the Law of the Sea (UNCLOS), except for MPAs in the Antarctic Ocean, are within areas of national jurisdiction and are designated and managed by countries in accordance with domestic laws, with insufficient attention given to the high seas and international seabed areas. To promote marine protection in areas beyond national jurisdictions, since 2018, the United Nations (UN) has initiated negotiations on an intergovernmental legally binding instrument for the conservation and sustainable use of marine biodiversity in areas beyond national jurisdictions, better known by its acronym BBNJ [20]. In June 2023, the BBNJ agreement was adopted, which forms a legal basis for the establishment of area-based management tools, including MPAs beyond national jurisdictions [21]. At the scientific and technical level, many UN and non-governmental initiatives have proposed maps for globally important marine areas using different criteria [22]. Seven criteria, including “uniqueness or rarity, special importance of the life history stage of the species, importance for threatened, endangered or declining species and/or habitats, vulnerability, fragility, susceptibility or slow recovery, biological productivity, biodiversity, naturalness”, have been used in the CBD framework to describe ecologically or biologically significant marine areas (EBSAs) in more than 75% of the world’s regions. These areas described by CBD have been directly used by the European Union, Japan, and small island countries to establish MPAs. However, the description of EBSAs has scientific gaps, such as a lack of data regarding the deepest parts of the ocean, and many EBSA descriptions were provided more than 10 years ago with no consideration for new data available. Moreover, the coverage of EBSAs is not yet universal, with no EBSAs described in the Southwest Atlantic [23]. If this description is used as the scientific basis for achieving the “30 by 30” initiative on the high seas and international seabed, it will be difficult to effectively protect the global marine ecosystem. Greenpeace [24] and the Pew Charitable Trusts [25] have also made recommendations for identifying 30% of the world’s marine conservation priority areas based on global species and habitat distribution data using spatial planning software.

Scientists have used various methods to prioritize marine conservation, including the use of leading and lagging indicators to define scoring criteria for marine ecosystem services [26], weighted overlay analysis of different habitat types [27], presence–absence or density surface models [28], systematic conservation planning [29], and calculating priority through an environmental sensitivity mapping approach for mapping environmentally sensitive assets [30]. Remote sensing imagery combined with habitat mapping and modeling [31] and rarity-weighted richness maps [32] have also been used for marine conservation priority identification. Moreover, systematic conservation planning approaches and optimization algorithms, including Marxan [33], Prioritizr [34], and Zonation [35,36], are commonly used to identify high-priority sites for biodiversity conservation. The research object includes single species such as sea turtles [37], coral reefs [38], seabirds [39], salmon [40], and sea mammals [41]; specific sea areas [42,43,44,45]; or Earth as a whole [33,46,47].

Some studies have analyzed the proposed priorities for marine biodiversity protection based on existing important marine areas for conservation [22,33,47] or the distribution of marine species [34,35,48]. In these studies, the dimensions of data and the methods used differ. Fan et al. used mitochondrial DNA barcode sequences and constructed a phylogenetic tree as the basis for a priority proposal. Belote et al. used 1697 marine species and subspecies in the continental US to compare the performance of the two methods. Gownaris et al. quantified the consensus of existing initiatives on MPAs and proposed gaps in globally important marine protection areas. Visalli et al. focused on maritime areas beyond national jurisdictions and used the species richness of fishes, marine mammals, marine invertebrates, seagrass, and benthic habitats for calculation. Compared to previous studies, this study focused on the conservation of rare and endangered marine species, including seabirds, considering the different habitats in the nearshore and deep ocean, as well as the five main catches that affect the livelihoods of fisherfolk on a global scale for priority calculation. The differences in the data and the methods used provide an opportunity to compare the outputs and take an integrated approach to choose priority areas for conservation to realize the target.

As policymakers seek to meet the “30 by 30” target in the global ocean, based on existing studies [22,34,35], this study focuses on typical nearshore, offshore, and deep-sea habitats, as well as the conservation of global rare, endangered, and commercially important marine species. This is achieved by considering abiotic factors, including temperature and salinity, and providing a marine conservation priority map of the global ocean. We also examine the overlap between EBSAs and existing MPAs with our result and conduct several discussions to provide suggestions on the establishment and management of protected area plans to achieve the considered target. Finally, we establish MPAs in areas beyond national jurisdictions under the BBNJ agreement.

2. Materials and Methods

2.1. Data Description and Sources

This study identifies global priority marine areas for protection at three levels: the marine species level, the habitat level, and the ecosystem level. A total of 162 layers of important habitats, rare and endangered species, and ecosystem distribution characteristics were selected as the basis for selecting priority marine areas for protection. All data used, including ocean features and biogeographic province distribution data, were obtained from publicly accessible sources on the Internet.

2.1.1. Surveyed Nearshore, Offshore, and Deep-Sea Habitats

Nearshore coral reefs, mangroves, salt marshes, kelp beds, and seagrass meadows, together with deep-sea seamounts, cold seeps, and hydrothermal vent ecosystems, are typical habitats that require priority attention and protection. Coral reefs are the most diverse marine ecosystem worldwide and are crucial for human survival and development [49]. Mangroves can secure the coastline from erosion, provide habitats for seabirds, fish, and invertebrates, and mitigate climate change [50]. Salt marshes are one of the most productive ecosystems, providing food sources and habitats for marine organisms in estuaries and coastal areas [51]. Kelp beds have high productivity and can help improve water quality, maintain biodiversity, sequester carbon, and prevent coastal erosion. Moreover, kelp beds can contribute to recreation and cultural services [52]. Seagrass meadows may help in mitigating ocean acidification due to their ability to raise pH and decrease DIC and pCO₂ [53]. They also serve as an important blue carbon habitat [54] and various ecosystem goods and services, including biodiversity maintenance, filtering, and sediment enrichment [55]. Cold seeps appear in seafloor cracks caused by tectonic activities, and the surrounding area forms a unique habitat and provides a haven for a variety of unique organisms [56]. Seamounts are also rich in deep-sea species, among which plankton, nekton, and benthos are quite different from those of the surrounding in terms of biomass, abundance, diversity, and so on [57]. Hydrothermal vents are underwater heat leaks formed in active volcanoes and seamounts, most of which are distributed in the continental plate boundary area. Hundreds of species live in and around hydrothermal vent ecosystems, many unique to the vent area [58].

Water depth is also an important factor that affects species distribution over seamounts. Research has shown that the composition of nekton and benthos distributed over seamounts varies with water depth [59], and different species live at different water depths. This study establishes layers based on the division of a range of ocean depths and divides them into four categories from the surface to the seafloor and even the abyss (the categories include shallower than 200 m, from 200 m to 800 m, from 800 m to 2000 m, and deeper than 2000 m) to distinguish different types of seamounts [60,61]. A seamount that is shallower than 200 m represents an area with a protrusion from the summit to the photic zone and hosts a particular community in the shallow depths. A seamount with a depth from 800 m to 2000 m represents an area with the distribution of vertically migrating animals (the scattering layer). A seamount with a depth deeper than 800 m forms the biogeographic area of the deep-sea bottom [60], characterized by the settlement of invertebrates and habitat for bathyal fishes, where the depth from 800 to 2000 m refers to the upper portions of the lower bathyal, with summits of seamounts at fishable depths; depths deeper than 2000 m refer to the lower portions of the lower bathyal [61]. Considering that hydrothermal vent ecosystems are distributed in seamount areas, only cold seeps and seamount data layers were used for deep sea areas in order to avoid duplicate calculations.

2.1.2. Endangered, Rare, and Commercially Valuable Marine Species

The establishment of MPAs considers not only environmental protection and conservation but also social and economic elements, including ensuring fisheries and fishing livelihoods, food security, and cultural values [62]. Focusing on the sustainable use of fishery resources, this study considers endangered species, rare marine species, commercial fish of significant economic value, and a high pelagic fishing volume when determining the selection parameters of priority marine areas for protection. To find a balance between the protection and utilization of living marine resources and ensure the livelihoods of fisherfolk, not only are rare and endangered species considered, but also important economic fish species with high pelagic fishing volume.

Based on “The State of World Fisheries And Aquaculture 2022”, Anchoveta, Alaska poll, Skipjack Tuna, Atlantic herring, Yellowfin Tuna, and Jumbo flying squid with a high global catch were selected as representative species [63]. We are also aware that the construction and management of an MPA may have a certain impact on the livelihoods of fisherfolk, and we have proposed targeted recommendations in Section 4.1 [64].

A total of 114 species of rare and endangered marine organisms listed in the “IUCN Red List of Threatened Species” were included in the model [33], including 44 species of fish, 25 species of reptiles, and 45 species of marine mammals [65]. Furthermore, as the distribution of seabirds may vary with breeding sites, age, time of day, and the seasons, and as some seabirds are opportunistic feeders that disperse widely, it is hard to define specific areas or habitats for marine protection [39]. We used the Important Bird and Biodiversity Areas (IBAs) established by BirdLife International [66] to represent the spatial distribution of seabirds that require consideration. IBAs in the ocean are described by BirdLife International based on satellite tracking data, marine surveys, and the research literature. There are currently 2621 seabird areas, 38% of which include a significant marine component, and others are coastal areas such as seabird breeding colonies [67]. In addition, this study considers global ship activity using Automatic Identification System (AIS) data of global vessels for the whole year of 2023 to delineate hotspots that are highly influenced by human activity.

2.1.3. Abiotic Elements

In addition to the above data layers, the current scope and technical limitations of deep-sea surveys were considered, given that the species distribution in existing survey data cannot fully reflect the actual situation of the deep sea. To better reflect the impact of the spatial distribution of abiotic factors in the ocean, such as cold water masses, hypoxic areas, temperature, salinity, dissolved oxygen, and ocean currents, this study drew inspiration from the classification of global marine habitats reported by Sutton et al., which incorporates ecosystem classification layers into the model [68], thus representing different types of marine ecosystems worldwide. This could meet the predetermined protection goals of various types of habitats and compensate for the lack of deep-sea surveys in the current survey and the absence of deep-sea species on the IUCN Red List. Global marine ecosystems were divided into 33 categories, including 20 types of coastal and nearshore ecosystems and 13 types of far-reaching marine ecosystems [68].

2.2. Methodology

2.2.1. Research Area and Data Pre-Processing

Referring to the scope of the “30 by 30” target, the research scope of this study covers all parts of the ocean from the surface to the floor, including territorial waters, exclusive economic zones (EEZs), the outer continental shelf, high seas, and international seabed areas. To facilitate layer comparison and subsequent calculations, all data were processed into grid layers of the same extent and grid size, with 4377 × 1996 grid units (grid size 0.083° × 0.083°) and the same coordinate system, “the 1984 World Geodetic Coordinate System.” Specifically, layers of point formats were interpolated as a separate raster map layer using the kernel density estimation function, then normalized from 0 to 1 using the Raster Calculator in ArcGIS 10.5. Layers of surface formats were converted to raster layers, with rasters with data being assigned a value of 1 and the rest assigned 0. To reduce the repetitive time and effort to perform each layer, the iterator of ModelBuilder was used for some level of automation.

2.2.2. Priority for Protection Calculation

This study used ArcGIS 10.5 and Zonation software (version 4.0.0) for priority calculation. Zonation is land-planning software based on ecosystem analysis and conservation prioritization at large spatial scales [36]. It is widely used to establish terrestrial habitats, species conservation areas [69], and marine protected areas [70,71]. The Zonation algorithm makes it possible to find a balance among multiple categories of biodiversity features—such as different species, habitats, and ecosystems—by dividing the study area evenly into several smaller units and calculating and ranking the priority order of the elements in each unit to produce a hierarchical prioritization of the conservation value of a study area. The results were achieved by repeatedly removing the units in the remaining unit set that caused the least marginal loss to the overall ‘conservation value’ and ranking all units.

After several attempts, the additive benefit function was chosen for this work, and the distortion factor was set to 100 to achieve a balance between the speed of computation and reproducibility of the results; the weights of each type of parameter took the value of 1. The “Additive benefit function” enables convergence to a solution to find a proportional coverage solution for data in order to identify prioritized areas containing multiple species or habitat layers, rather than considering only areas where a particular species or habitat is very rich to find a minimum set of solutions covering all data categories [51]. The distortion factor used in the model indicates the number of grid cells removed in each iteration.

2.2.3. Visualization and Comparison

After calculation, the conservation priority order was reclassified, filtered, and ranked using ArcGIS 10.5. To consider the range from coastal and nearshore areas to the open ocean and deep ocean trenches in the adoption of global marine protection priority calculations, 30% of the global marine protection priorities were selected within and beyond national jurisdictions using the mask function in ArcGIS 10.5 in the case of data gap of different areas. Both within and beyond national jurisdictions, priority areas were reclassified and ranked in order of protection priority using the reclassify function and Raster Calculator to form a global marine conservation priority distribution map.

In order to compare the result with existing MPAs and EBSAs, the MPAs and EBSAs layer was first converted to the same raster size as the results above and assigned values of 1 separately. The blank area was assigned 0 and then analyzed by overlaying the two layers with the Raster Calculator in ArcGIS 10.5, then calculating the distribution promotion of existing MPAs in priority areas via the number of grids with different values.

3. Results

3.1. Description of Global Priority Marine Areas for Protection Layout

As shown in Figure 1, the conservation priority of coastal and nearshore areas is much higher than that of the open ocean. Considering that global marine protection and conservation will revolve around the “30 by 30” initiative in the next decade, this article proposes the top 30% of global priority marine areas for protection by analyzing the model’s results.

The top 30% of the global marine protection priorities mainly include the Arabian Sea, the Chagos–Laccadive Ridge, the marine areas around Madagascar and the Southwest Indian Ocean region, the Western Pacific seamount area and the Eastern Pacific seamount area, the Emperor seamount chain, the Tasman Sea, the North Pacific transitional zone, the Southeast Pacific Ocean, the coral reef delta, and the hydrothermal region of the Midwestern ridge of the North Pacific Ocean. It also includes the Argentine Basin, the Sargasso Sea, the hydrothermal region of the Midwestern ridge of the North Pacific Ocean, the equatorial high productivity area of the Atlantic Ocean, and other sea areas in the Atlantic Ocean. The top 5% of the most protected areas are mainly distributed along the Atlantic and Indian Ocean coasts, the Mediterranean, and the Western Pacific seamount region. Among them, the priority of marine protection in territorial waters and EEZs is much higher than in areas beyond national jurisdictions (Figure 2).

3.2. Distribution of Priority Marine Areas for Protection from the Coastline to Deep Ocean Trenches

In the top 30% of global marine protection priorities, the priority of marine protection and conservation in territorial waters and EEZs is much higher than that in marine areas beyond national jurisdictions. Among the top 5% of areas with priority protection, 82.42% are located in territorial waters and EEZs, while 17.58% are located in high seas and international seabed areas beyond national jurisdictions (see

Table 1. The distribution of protection priority areas. The table indicates the proportions of the 6 categories of maritime areas with different priorities within and beyond national jurisdiction, respectively.

Order of Priority Marine Areas for Protection	Percentage of Territorial Sea and Exclusive Economic Zone	Percentage of High Seas and International Seabed Areas
Top 5%	82.42%	17.58%
From 5% to 10%	71.27%	28.73%
From 10% to 15%	53.16%	46.85%
From 15% to 20%	15.09%	84.91%
From 20% to 25%	0.63%	98.47%
From 25% to 30%	0.16%	99.84%

). However, over 95% of the areas with protection priority of 20% to 30% are beyond national jurisdictions. On the one hand, this is due to the richer biodiversity in the coastal and nearshore waters, which are habitats for numerous marine mammals, reptiles, fish, and seabirds, as well as important habitats such as mangroves, kelp beds, and coral reefs with high conservation value. On the other hand, the data on marine species, habitats, and ocean features used in this study mainly rely on open-source data released after global marine scientific surveys. Due to the abundance of surveys in the offshore area compared to the high sea and international seabed, it is easier to be more accurate in determining the areas that need to be protected in the coastal and nearshore marine areas.

The protection priority of coastal and nearshore areas is higher. In contrast, in the high sea and international seabed, due to the lack of systematic scientific surveys, the selection of protected areas largely relies on available scientific cognition and model speculation, resulting in a lower priority of calculated protection. To more scientifically lay out marine protected areas globally, it is more feasible to first start from the waters under national jurisdiction, and each country should prioritize the establishment of protected areas in its own territorial waters and EEZs in accordance with domestic laws in order to establish a scientific and reasonable system of marine protected areas. Simultaneously, countries could actively cooperate in conducting scientific investigations in marine areas beyond national jurisdictions, for instance, through international cooperation of big science programs under the Ocean Decade. When the background data are sufficient, countries can scientifically determine the priority order for protecting high seas and international seabed areas.

4. Discussion

4.1. Comparison with Marine Protected Areas and Ecologically or Biologically Significant Marine Areas

At present, there are 18,431 MPAs worldwide, representing 8.17% of the global marine area. In contrast, all established MPAs are located within marine areas of national jurisdiction, except those in the Antarctic Ocean (including the Ross Sea region Marine Protected Area and the South Orkney Islands Southern Shelf Marine Protected Area). A total of 27.96% of the world’s MPAs are located in the top 30% of the effective order of protection when compared to the priority areas for marine protection within the jurisdiction, with 12.42% of the MPAs located in the top 10% of the effective order of protection (

Table 2. The distribution proportion of existing marine protected areas (MPAs) and ecologically or biologically significant marine areas (EBSAs) in priority areas. The table indicates the proportion of MPA and EBSA areas overlapping with sea areas of different protection priority orders to the total MPA and EBSA area.

Order of Priority Marine Areas for Protection	Proportion of Existing Marine Protected Areas	Proportion of Ecologically or Biologically Significant Marine Areas
Top 5%	5.26%	6.59%
From 5% to 10%	7.16%	7.12%
From 10% to 15%	7.29%	7.27%
From 15% to 20%	5.28%	2.29%
From 20% to 25%	1.75%	10.54%
From 25% to 30%	1.22%	8.31%
Sum	27.96%	42.11%

). Clearly, the reason for such a large difference in results is the difference in the scope of MPAs and the method and data used for their selection (Figure 3). As the current MPAs are almost all selected within national jurisdictions based on the domestic laws of each country and a large part of the data used to select MPAs in each country is not readily available online and in open-source forums, our findings do not overlap well with existing protected areas.

An EBSA, described under the CBD regional expert workshops, is a type of marine ecosystem area that has special ecological importance and biological value, such as marine species breeding grounds, spawning grounds, migration corridors, or food resources. Due to efforts by experts for more than a decade, more than 300 EBSAs have been described both within and beyond national jurisdictions at a variety of depths from the surface to the deep sea [23,72]. The comparison showed that approximately 42.11% of the described EBSAs overlapped with the top 30% of priority protected areas, with 13.71% of the EBSAs overlapping with the top 10% of priority protected areas (Table 2) (Figure 4).

The difference in results between the two kinds of areas is due to differences in the used identification methods, as described by EBSAs through regional expert workshops held under the CBD. Only relevant countries, regional organizations, non-governmental organizations, experts, and scholars within a region are involved in the description, with technical support provided by the Commonwealth Scientific and Industrial Research Organization of Australia and the Marine Geospatial Ecology Laboratory of Duke University [23]. Using the Central Indian Ocean Basin as an example, this area was described as an EBSA, as it is a foraging area during the non-breeding season for four seabird species based on past research [73]. However, the data we used to assess the distribution of seabirds came from the IBA, and the Central Indian Ocean Basin was not identified as an IBA because of different identification methods [67], which led to different results. Considering that multi-species approaches using overall enclosure or diversity specifications are currently the main method for selecting MPAs [39,74] for seabirds, due to the variation in seabird distribution depending on their breeding site, age, or the time of year [39,75], it seems more reasonable not to identify this area as an MPA. Furthermore, many EBSAs have been described for more than 10 years, and objects of protection, such as marine migratory species or deep-sea ecosystems, were not considered in the description. Compared to the analysis methodology that only relies on available scientific information and models in this study, the description of EBSAs had a focus that is more in line with stakeholder participation [76]. This method is more feasible within a region and has high operability but entails strong expert subjectivity. Local support from stakeholders is crucial for the planning and ongoing management of MPAs, as it could make the rules of MPAs more acceptable, as well as increase trust and satisfaction [77]. In the future, it is recommended that the use of available scientific information and evidence support, stakeholder participation, and expert evaluation in the selection and planning of high seas protected areas be combined to improve the scientific nature of protected area planning.

4.2. Discussion on Management of Priority Marine Areas for Protection

Based on open-source data regarding species, habitats, and ocean features and using spatial analysis methods, this study takes global marine regions as the research object and identifies marine regions that need global priority protection. The mere proposal of MPAs does not guarantee actual ocean protection; effective management measures, enforcement [78], surveillance, and compliance with regulations are also decisive for MPAs [79]. The measures of an MPA vary widely from strict protection, with all extractive activities being prohibited, to areas that permit certain levels of extraction and human activities [80]. The different marine areas in Figure 1 should be protected in different ways. Although the protection priority order of different sea areas might be roughly at the same level, the specific protection objects and objectives are different, and establishing each MPA is a different task. It is necessary to adopt a “case-by-case” strategy when establishing an MPA and develop targeted management measures as well as monitoring, surveillance, and control tools that are based on the protection objectives and objects in different regions to protect the marine environment while considering normal marine activities and resource development and utilization.

Management measures of MPAs include routine measures related to human activities monitoring, fishing activity regulation, the establishment of biological rest periods, and the regulation of marine and terrestrial spaces like zoning or buffers [81]. Referring to the “Guidelines for Applying the IUCN Protected Area Management Categories to Marine Protected Areas”, MPAs are always divided into six categories (including Ia, strict nature reserve; Ib, wilderness area; II, national park; III, natural monument or feature; IV, habitat/species management area; V, protected landscape or seascape; and VI, protected areas the with sustainable use of natural resources) based on their management objectives [82], and different management measures from exclusionary protection to sustainable utilization are implemented for different categories of MPAs [83].

For example, in protected areas with a priority of 5% to 10%, the protection objects of the Southwestern Indian Ocean are unique seamounts and shoals, with rare and fragile species habitats [84] and some threatened seabird species [85]. An MPA should be established to protect seamount ecosystems, biodiversity hotspots near the seamount [86], and the migration routes of seabirds. Seamount habitats and ecosystems are put at risk by seabed mining and bottom trawling, which are the main human activities in this region [84]. Some deep-sea corals and sponges near the seamount are particularly sensitive to the impacts of bottom fishing [87]. Therefore, the management measures of MPAs in this region should focus on deep-sea mineral exploration, commercial mining, bottom fishing prohibition, catches or footprint limitation, bycatch mitigation, and complete observer coverage on all commercial fishing vessels. The protected objects in the Arabian Basin are the feeding area of petrels [88]. The region is also home to threatened species, including baleen whales, sea turtles, and dolphins [89]. As the main human activities in this area include fishing and shipping, measures of MPA here could focus on improving the environmental protection standards for shipping and fishery and implementing management measures such as vessel noise reduction, speed reduction, marine litter discharge reduction, bycatch mitigation, and low-carbon clean vessel fuels [89].

Management measures should be designed to balance normal marine activities and resource exploitation and should not be generalized to all protected areas. Excessively strict protection measures would greatly increase the cost of MPAs and affect the livelihoods of local communities, such as fisherfolk [90]. In particular, some activities have little impact on the environment, such as maritime scientific investigations and submarine cable laying [91]. Targeted management measures with time bounds could be stratified and graded according to the protected species. Moreover, management measures should consider the livelihoods of fisherfolk, including proposing alternative livelihoods, involving all stakeholders and the wider community of fisherfolk in MPA management [64,92].

4.3. Limitations

There were limitations in this study. We extensively used data on marine species, habitats, ocean features, and biogeographic provinces to describe priority areas for marine conservation, but all data were acquired from open sources. Spatial and temporal gaps of available data are a general limitation for biodiversity conservation [93], and there were uneven data on the distribution of specifications and habitats in different sea areas [94], such as in the South Atlantic [95], which likely influenced our results. Meanwhile, we also note that research technologies regarding marine biodiversity and habitats are emerging, such as the use of eDNA sampling and remote sensing techniques, which could help fill the gaps in data used for MPA identification [34,96]. In addition, the use of data and models with the participation of experts and the public, in line with the description of EBSAs, will undoubtedly be beneficial in a better “30 by 30” proposal.

4.4. Recommendations

Two recommendations are made in this paper to better contribute to the global construction of MPAs and other area-based management tools for marine biodiversity conservation and protection.

First, considering that laws and guidelines for establishing MPAs beyond national jurisdiction are still being developed [97], priority is given to promoting networks of marine protected areas within national jurisdictions. At present, the area of marine protection in waters under the jurisdiction of many countries is seriously inadequate. In China, for example, the total area of marine protected areas only accounts for 4.1% of the area of marine areas under the country’s jurisdiction, far short of the intended protection target. Most protected areas are in the territorial seas, with a serious lack of marine protection in EEZs [98]. To achieve effective protection of the oceans, it is first necessary to conduct scientific surveys around China’s Bohai, Yellow, East, and South China Seas to obtain basic data for designating MPAs or other area-based protection or management measures. By combining data on the specific environmental and species distribution status and human activity distribution of the four sea areas, the selection and management plan of MPAs within the exclusive economy can be determined, starting with the establishment of well-designed, well-managed, and strongly enforced MPAs in EEZs based on solid scientific data.

Second, to promote the construction of global protected areas more quickly and at the same time guarantee the right to participation for low- and middle-income countries, it is necessary to promote systematic joint marine scientific surveys in the high seas and international seabed areas, with the participation of all countries, in order to map the distribution of species and habitats in the high seas at an early stage. It is recommended that international scientific programs such as the “2021–2030 United Nations Decade of Ocean Science for Sustainable Development” and the “Global Ocean Observing Programme” be used as a means of scientific capacity building and public awareness raising in low- and middle-income countries and that countries cooperate in conducting scientific surveys. Scientific data should be obtained to support the selection of protected areas in the high seas and international seabed areas, priority areas for global marine biodiversity conservation should be identified as soon as possible, and relevant proposals should be made.

5. Conclusions

The systematic identification of global conservation priority considering nearshore and offshore species, habitats, and abiotic elements, as well as the sustainable use of marine resources, plays an important role in identifying and managing MPAs at the global scale to ensure marine protection and conservation. This study provides a global-scale proposal for the selection of priority areas for marine protection under the scenario of achieving the “30 by 30” target. Feasible recommendations to identify MPAs were proposed based on comprehensive scientific evidence and stakeholder participation in the future. Furthermore, in order to improve the effectiveness of marine protection, scientific delineation of the boundaries of protected areas is necessary, as well as the development of targeted management measures based on the specific objects to be protected and the threats affecting them.