An analysis of the most comprehensive (∼23,000 species) and high-resolution data on the global distribution of marine biodiversity [] shows that the geographic ranges of 93% (n = 21,322) of all marine species overlap with marine wilderness areas ( Table S2 ). These overlaps are higher for species with large home ranges, such as marine mammals (8.4% average overlap), and lower for groups with more coastal distributions, such as reptiles (2.6% average overlap; Table S2 ). Marine wilderness overlaps with areas of high species richness, range rarity, and proportional range rarity ( STAR Methods Figures S3 and S4 ), as well as with previously identified hotspots of both functional diversity, such as the Gulf of Carpentaria in Australia [], and of species endemism, such as the Desventuradas islands West of Chile []. On average, global wilderness areas have 31% higher species richness, 40% higher range rarity, and 24% higher proportional range rarity than non-wilderness areas, though this varies substantially across marine ecoregions ( Table S3 ). For example, wilderness areas in the Solomon Sea have more than three times higher range rarity values than non-wilderness areas ( Table S3 ). Conversely, in the Banda Sea, wilderness areas have approximately three times lower species richness than non-wilderness areas ( Table S3 ).

Global wilderness extent varies considerably across the ocean, with substantial wilderness in the southern high seas and very little in the northern hemisphere ( Table 1 ). For example, 26.9% (25 million km) of the Southern Cold Water realm is defined as global marine wilderness, compared to <0.3% (13,263 km) of the Temperate Northern Atlantic ( Table 1 ). This difference is due to significant fishing and shipping activity occurring in the waters around northern Asia, Europe, and North America []. Global marine wilderness extent also varies across ecosystem types and is generally much higher offshore than in coastal regions ( Figure 2 ). All coastal ecosystems (except for naturally extensive soft-bottom areas), have <100,000 kmof wilderness remaining ( Figure 2 ). In contrast, almost 40 million km(12%) of deep benthic soft-bottom habitat is classified as wilderness, and all offshore ecosystems (except seamounts and the hard bottom coastal shelf) have retained >200,000 kmof wilderness ( Figure 2 ).

Our method identified 13.2% (∼55 million km) of the world’s ocean as global marine wilderness ( Figure 1 ), primarily located in the high seas of the southern hemisphere and at extreme latitudes. Most wilderness within exclusive economic zones (EEZs) is found across the Arctic (6.9 million km) or Pacific island nations (2.7 million km Figure 1 ), although there is substantial wilderness in the EEZs of some other nations, such as New Zealand (25% of EEZs, 1.1 million km), Chile (6% of EEZs, 120,000 km), and Australia (4.3% of EEZs, ∼350,000 km). This is most likely due to low human populations in these areas and, in some cases, sea ice preventing human access to the ocean ( Figure S2 ). However, with sea ice rapidly disappearing in the Arctic [], some wilderness loss has already occurred in previously ice-covered areas ( Figure S2 ), and this trend is likely to accelerate as sea ice continues to decline.

Identifying marine wilderness requires finding biologically and ecologically intact seascapes that are mostly free of human disturbance []. Here we do so by mapping those areas that have low impact across all human stressors and also have a low cumulative impact, as even low levels of human activity can significantly impact some critical aspects of biodiversity (e.g., mobile top predators []). To identify marine wilderness, we used the most comprehensive global data available for 19 human stressors to the ocean (detailed summary in Table S1 ) and the cumulative impact of these stressors []. We first identified areas within the bottom 10% for every separate human stressor (e.g., demersal fishing and fertilizer runoff; Table S1 ) and then applied a secondary classification to only include areas also within the bottom 10% of total cumulative impact at the global scale (see STAR Methods ). Because the impacts of climate change are widespread and unmanageable at a local scale, there are significant variations in exposure and vulnerability across marine ecosystems (e.g., coral reefs versus deep sea), and including climate variables would result in no wilderness remaining ( Figure S1 ), we excluded climate change variables (temperature and UV anomalies, ocean acidification, and sea level rise) from the individual stressor analysis but included them in the cumulative impact analysis ( Table S1 ).

Realm-specific wilderness identifies the least impacted places within each ocean realm, meaning that the extent varies considerably, as it is dependent on the total level of human impact within realms. Consistent with global marine wilderness, most realm-specific wilderness is found in the high seas (66%; Figure 3 ). There is much more global wilderness than realm-specific wilderness overall ( Table 1 ), and the location of wilderness areas differs substantially ( Figures 1 and 3 ). In highly impacted realms (e.g., Temperate Northern Atlantic), the extent of realm-specific wilderness is four times that of global wilderness ( Table 1 ). Conversely, areas of low human impact (e.g., the Arctic) have far less realm-specific wilderness than global wilderness ( Table 1 ). Given the widespread nature of human impacts in some ocean realms [], realm-specific wilderness can occur in places with significant human activity, such as the Gulf of Mexico and the Persian Gulf. Although these sites are under considerable human influence, they still represent some of the least impacted places within each ocean realm and are therefore important to protect.

A primary objective of conservation is to achieve representative protection of biodiversity []. Oceanic realms and ecoregions are an increasingly important biogeographical classification for conservation planning and assessment [] and are important surrogates for biological representativeness when assessing global marine protected area (MPA) coverage []. We therefore mapped realm-specific wilderness by identifying areas within each ocean realm [] that have little impact (bottom 10%) from 15 anthropogenic stressors and also have very low (bottom 10%) cumulative human impact ( STAR Methods Table S1 ).

Realm-specific wilderness has much higher MPA coverage than global marine wilderness, with half of all realms having >50% wilderness protection ( Table 1 ). This is most likely because, when compared to global marine wilderness, there is more realm-specific wilderness in coastal waters where most MPAs are designated []. However, some realms have very poor wilderness coverage, with the Southern Ocean, Northern Cold Water, and Atlantic Cold Water realms all having <0.1% of realm-specific wilderness protection ( Table 1 ).

Considerably more global marine wilderness remains in offshore ecosystems (49.7 million km) than in coastal ecosystems (5.5 million km Figure 2 ), but the proportion of protected wilderness is similar (4.4% and 4.8%, respectively). In coastal ecosystems, the vast majority of protected wilderness (93%) is in soft-bottom areas, rather than habitats such as rocky reefs or coral reefs that people depend on for food and income [] ( Figure 2 Table S4 ). However, despite having low wilderness extent and areal protection, these ecosystems have high proportional levels of protection, with 66% and 26% of rocky reef and coral reef wilderness being covered by MPAs, respectively ( Table S4 ). A substantial amount of wilderness in these ecosystems is contained in large, remote MPAs, such as the British Indian Ocean Territory MPA []. Offshore ecosystems generally have more protected wilderness area than coastal ecosystems ( Figure 2 ) but lower proportional wilderness protection ( Table S4 ).

We found that only 4.9% of global marine wilderness (2.67 million km) is inside MPAs ( Table 1 ), despite 6.97% of total ocean area being under protection. This protection occurs almost exclusively within national waters, with 12% (2.65 million km) of global wilderness within EEZs protected, but only 0.06% (0.02 million km) of wilderness in high seas protected. Global wilderness protection is high in some populated regions, with 98% protected in Temperate Southern Africa and 17% protected in the Central Indo-Pacific ( Table 1 ). However, these areas also have very little total wilderness left (<5%; Table 1 ), suggesting that MPAs play a crucial role in preserving the small amount remaining. Wilderness protection is much lower in remote areas, such as the Southern Ocean and Northern Cold Water realms, where few MPAs are designated ( Table 1 ).

Marine wilderness is often overlooked, both in global conservation policy and in national conservation strategies, because these areas are assumed to be free from threatening processes and therefore not a priority for conservation efforts []. Our results follow recent terrestrial analyses that debunk the myth that wilderness is not threatened [], as we show only 13% of global marine wilderness remains. International policies are often blind to the benefits that flow from intact, functioning ecosystems, and there is no text within the CBD or the United Nations World Heritage Convention that recognizes the importance of retaining large intact landscapes or seascapes []. Similarly, national-level conservation plans tend to focus on securing under-pressure habitats or endangered populations [], rather than multi-faceted strategies that also focus on wilderness protection. Although conservation efforts in high-biodiversity, high-pressure regions (e.g., the Coral Triangle and Caribbean) are very important, they should be complemented by proactive action to prevent human pressures from eroding Earth’s marine wilderness areas.

Marine wilderness areas may also be well placed to resist and recover from the impacts of climate change, though the evidence for this is mixed []. There are a number of studies showing that less degraded ecosystems can return more quickly to their original state after disturbances (including climate stressors) than more degraded ones []. Furthermore, there is also some evidence that local stressors can reduce ecosystem resilience to climate change, meaning that wilderness areas may have increased climate resilience []. However, local stressors do not always affect susceptibility to climate change [], and some areas of low anthropogenic activity are already severely impacted by climate change []. Nevertheless, conserving wilderness areas will provide numerous biodiversity benefits, including preserving unique species compositions and functional traits, and these areas may also be resilient to climate change.

Marine wilderness loss may impact the ability of nations to achieve global conservation goals within key multilateral environmental agreements, such as the Convention on Biological Diversity (CBD), which mandates inclusion of at least 10% of marine areas in effectively managed and ecologically representative MPAs by 2020 []. Achieving a truly representative MPA network will require the protection of global and realm-specific wilderness alongside imperiled biodiversity-rich areas, because wilderness areas support unique species compositions and higher biomass than populated areas []. Wilderness areas can also exhibit extremely high endemism [] and harbor functional traits rarely found in areas of higher impact []. Furthermore, although many marine wilderness areas are located in deep-water areas ( Figure 1 ), recent research shows that these places are not as species impoverished as once thought, as they hold significant biodiversity [] and maintain crucial ecosystem processes [].

Human pressures across the ocean are increasing rapidly, and nowhere in the sea is entirely free of human impacts []. We show that there is very little marine wilderness in coastal areas, with most remaining wilderness relegated to extreme latitudes or the high seas ( Figure 1 ). Although there are vast differences in the amount of wilderness remaining across marine ecosystems, the level of wilderness protection is low in most ecosystems ( Figure 2 ). International conservation policies should now recognize the values of wilderness and target conservation actions toward reducing threats in these areas to ensure their retention.

Future Conservation Actions

29 Agnew D.J.

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Pitcher T.J. Estimating the worldwide extent of illegal fishing. Multilateral environmental agreements should now recognize the importance of wilderness and the increasing threats it faces, both on land and in the ocean. Such recognition will help drive large-scale actions needed to secure wilderness into the future. These actions will vary across nations and regions, but they should focus on human activities that threaten wilderness. In the ocean, this includes preventing overfishing and destructive fishing practices, minimizing ocean-based mining that extensively alters habitats, and limiting runoff from land-based activities. Better enforcement of existing laws is also needed to prevent illegal, unreported, and unregulated fishing, which makes up 10%–30% of global catch [].

27 Hughes T.P.

Kerry J.T.

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Anderson K.D.

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et al. Global warming and recurrent mass bleaching of corals. 30 Perry A.L.

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Reynolds J.D. Climate change and distribution shifts in marine fishes. 31 Pinsky M.

Fogarty M. Lagged social-ecological responses to climate and range shifts in fisheries. 18 Harris P.T.

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Rice J.C. Arctic marine conservation is not prepared for the coming melt. 27 Hughes T.P.

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et al. Global warming and recurrent mass bleaching of corals. Along with ocean-based threats that erode wilderness, it is crucial to consider the impacts of climate change, which are already affecting marine biodiversity []. Although we include climate change in our secondary cumulative impact classification, inclusion of climate variables in our individual stressor analysis resulted in almost zero marine wilderness remaining ( Figure S1 STAR Methods ). Our results must therefore be interpreted with the caveat that marine wilderness is already, and will continue to be, impacted by climate change. Although considering the direct impacts of climate change (e.g., temperature increases) is crucial, it is also important to predict and counter threatening human responses to climate change, such as shifting fishing grounds [] or the opening of previously ice covered areas for shipping and fishing []. Given the devastating recent impacts of climate change on particular marine ecosystems (e.g., coral reefs []), we believe that priorities for wilderness protection could be informed by research assessing where such areas have been, or are likely to be, significantly impacted by climate change and where they can act as climate refugia.

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Silliman B.R. A blueprint for blue carbon: toward an improved understanding of the role of vegetated coastal habitats in sequestering CO2. 35 Devillers R.

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Watson R. Reinventing residual reserves in the sea: are we favouring ease of establishment over need for protection?. 36 Klein C.J.

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et al. Prioritizing land and sea conservation investments to protect coral reefs. 37 Kroodsma D.A.

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et al. Tracking the global footprint of fisheries. Due to large-scale erosion of marine wilderness, those remaining areas are, almost by definition, irreplaceable—representing some of the last marine areas affected by no, or very low, human pressure. Protecting wilderness areas will help preserve large, biologically connected ecosystems []; species with large home ranges (e.g., tuna []); and hotspots of functional traits and endemic species []. It will also directly benefit humanity by preserving the carbon mitigation and adaptation values of intact marine ecosystems []. However, it is crucial to prioritize wilderness conservation to those areas most at risk of being lost and to not repeat past mistakes by designating MPAs to minimize conflict with other activities (e.g., fishing and mining []). In highly impacted regions and coastal ecosystems, retaining intact ecosystems will most likely require supplementing MPAs with other interventions to prevent impacts, such as land-based regulations to minimize sediment runoff []. Given that such little global marine wilderness remains in coastal areas, our realm-specific wilderness map ( Figure 3 ) is useful to help direct such actions. It is also important to recognize that as with all global analyses, our wilderness maps rely on imperfect data, and we anticipate that refinements will occur as new data become available (e.g., Global Fishing Watch []), ensuring that wilderness is mapped with increasing precision.

38 Watson R.A.

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Richardson A.J. Pelagic protected areas: the missing dimension in ocean conservation. 32 Wilhelm T.

Sheppard C.R.C.

Sheppard A.L.S.

Gaymer C.F.

Parks J.

Wagner D.

Lewis N. Large marine protected areas – advantages and challenges of going big. 40 Game E.T.

Grantham H.S.

Hobday A.J.

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Lombard A.T.

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Gjerde K.

Bustamante R.

Possingham H.P.

Richardson A.J. Pelagic protected areas: the missing dimension in ocean conservation. 37 Kroodsma D.A.

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et al. Tracking the global footprint of fisheries. 41 United Nations General Assembly

International legally binding instrument under the United Nations Convention on the Law of the Sea on the conservation and sustainable use of marine biological diversity of areas beyond national jurisdiction. As technological advances drive human impacts farther from land and deeper into the sea, it is also essential to consider the three-dimensional nature of the ocean. For example, fishing gear improvements have increased the mean depth of industrial fishing by 350 m since 1950 [], and there are now almost 2,000 oil and gas wells operating deeper than 400 m []. Targeting conservation actions toward specific threats at specific depths will provide better protection of biodiversity across the entire water column. Wilderness conservation will also require an increased focus on high seas management. Although it is legally challenging, prioritizing conservation actions in at-risk areas beyond national jurisdiction is crucial for dealing with expanding human threats []. There is growing momentum behind the designation of large oceanic MPAs (e.g., Big Ocean []), and there are now extensive data to facilitate defensible selection and design of these large pelagic MPAs to protect high-seas wilderness []. Current difficulties with ensuring enforcement and compliance in these remote areas are beginning to be overcome, with recent advances in satellite and remote vessel-monitoring technology, such as Global Fishing Watch []. The need for improved high-seas management is also now being recognized by the international community, with the UN currently negotiating the “Paris Agreement for the Ocean”—a legally binding high-seas conservation treaty to be established under the existing Law of the Sea Convention [].