Table 1 Scenarios conducive to achieving the best aspirational outcomes towards rebuilding marine life

From: Rebuilding marine life

Rebuilding wedgesSaltmarshesMangrovesSeagrassCoral reefsKelpOyster reefsFisheriesMegafaunaDeep-sea habitats
Protect speciesLowLowLowLowLowHighCriticalCriticalCritical
Harvest wiselyLowCriticalLowHighHighCriticalCriticalCriticalCritical
Protect spacesCriticalCriticalMediumHighMediumCriticalHighHighCritical
Restore habitatsCriticalCriticalHighMediumMediumCriticalMediumMediumMedium
Reduce pollutionMediumMediumCriticalCriticalCriticalHighMediumMediumHigh
Mitigate climate changeHighHighHighCriticalHighHighHighHighHigh
Recovery targets by 2050Substantial to completeSubstantial to completeSubstantial to completePartial to substantialSubstantial to completeSubstantial to completeSubstantial to completeSubstantialPartial to substantial
Key ActorsGovernment, civil society and NGOs.Government, civil society and NGOs.Government, civil society and NGOs.Government, tourism operators, fishers organizations, civil society and NGOs.Government, fishers organizations and civil society.Government, fishers organizations, NGOs and civil society.Government, fishers organizations and civil society.Government, fishers organizations, NGOs and civil society.International seabed authority, state and federal governments, mining/exploration companies, civil society and fishing industry.
Key ActionsProtection of remaining saltmarshes, providing sources of sediment, potentially planting native species, providing space for landward migration and restoring hydrological connections.Protection, provide alternative livelihoods for dependent communities, provide space for landward migration, restore hydrological connections, maintain sediment supply and restore damaged forests.Reduce nutrient inputs, protect, avoid physical impacts, and conduct restoration projects.Ambitious reduction in greenhouse gas emissions. Reduce excess sediment and nutrient inputs, improve water quality, protect reefs, rebuild food webs and restore damaged reefs.Restoration requires removal of excess herbivores, by rebuilding their predators, and a reduction in sediment loads on rocky substrates and kelps.Protect remaining reefs, prohibition of natural reef harvests, improve water quality and restore reefs.Reduce overfishing, bycatch and incidental mortality, ban destructive fishing practices, protect spawning/breeding areas and nursery grounds, and remove perverse incentives.Protect, reduce bycatch, reduce incidental mortality (ship strikes, entanglement, ghost gear), reduce pollution (noise, debris, chemical), protect breeding/haul-out sites, safeguard migration routes and reduce competition with fisheries.Regulate industries that operate in the deep sea. Ban deep-sea fishing and impose a moratorium on deep-sea mining until technologies free of impact are available. Improve environmental safety of oil and gas operations. Develop facilities to test technologies before real-ocean deployment.
Key OpportunitiesBlue Carbon and coastal defence strategies against storms and sea-level rise, links to management for enhancing water quality, food provision and biodiversity strategies.Blue Carbon and coastal defence strategies against storms and sea-level rise, links to management for enhancing water quality, food provision and biodiversity strategies.Blue Carbon and coastal defence strategies against storms and sea-level rise, links to management for enhancing water quality, food provision and biodiversity strategies.Link to coastal defence, food provision and biodiversity strategies.Emerging role in Blue Carbon, water quality and biodiversity strategies.Link to water quality improvement, biodiversity and coastal protection strategies.Sustainable seafood, MSC-certified fisheries, develop sustainable aquaculture to reduce pressure on wild stocks.Marine wildlife tourism, cultural benefits and ethics.High percentage of unique, unexplored habitats and new species, potential for novel products important in fighting/preventing disease. Huge carbon-sink potential.
Key BenefitsImproved fisheries, protection from sea-level rise and storm surges, recreational and cultural benefits, hunting.Improved fisheries, biodiversity and coastal defence, recreation and cultural benefits.Protect shoreline from erosion and rebuilding biodiversity and fisheries.Provision of fish, protection from sea-level rise and storm surges, recreational and cultural benefits.Enhanced fisheries.Improved water quality, increased habitat, recreational and cultural benefits, food sources.Improved quality and quantity of seafood supply.Increased connectivity among ocean basins, enhanced nutrient cycling and ocean productivity.Huge potential for discoveries and new resources. Avoidance of irreversible damage.
RoadblocksMany saltmarshes are filled, landward migration impeded because of infrastructure, not enough sediment supply, sea-level rise, increased decomposition rates with rising temperatures and/or excess nutrient loading, reverting land use.Alternative land uses and infrastructure, lack of alternative livelihoods and incentives for communities, uncertainties around climate change impacts.Infrastructure (for example, areas occupied by harbours), severe and frequent heat waves with climate change.Dependence on climate change trajectories, mortality with ocean warming, ocean acidification and increased cyclone activitiy.Climate change at the edge of the equatorial range of kelp species, high herbivore pressure and sediment accumulation on rocky substrates.Poor management of fisheries on remaining reefs, degraded habitats, restoration costs, increased prevalence of disease with rising water temperatures.Cumulative impacts from fishing, pollution, habitat alterations, changing distribution ranges, habitats and food due to climate change.Losses due to extinction, continued impacts from ship strikes, pollution, habitat alterations, changing habitats and food due to climate change.Slow and uncertain recovery and success of, hugely costly restoration, which will be extremely difficult and expensive. Development multi-governmental cooperation, buy-in, and action towards this goal.
Remedial ActionsRestore hydrological flows and sediment delivery, restore native plants, restore transitional upland boundaries where possible, increase incentives to relocate users.Increase incentives to improve management and develop alternative livelihoods, restoration, landscape planning for landward migration.Compensatory restoration, improve water quality and reduce local stressors.Ambitious efforts to mitigate climate change and manage to improve resilience.Restore with thermal-resistant genotypes and reduce sediment delivery to rocky habitats.Protect remaining reefs, large-scale restoration efforts, defining success with not just increased harvest in mind but the many other benefits oyster reefs provide.Create MPAs as refuge sites, restore coastal breeding/nursery sites to aid recovery, develop breeding programmes for critically endangered speciesCreate MPAs as refuge sites, safeguard migration routes, restore coastal breeding/nursery sites to aid recovery and develop breeding programmes for critically endangered species.Protect what has not been damaged or destroyed and prevent further destruction in places that have already been affected. Widespread education on the fragility of the deep sea and benefits of deep-sea ecosystems, strengthen regulation, decrease pollution and recycle products that require rare earth metals.
  1. Actions include rebuilding wedges, assessment of the maximum recovery targets by 2050 if these wedges are fully activated, as well as key actors, opportunities, benefits, roadblocks and remedial actions to rebuild different components of marine life (priority increases from low to critical). See Supplementary Information 3 for details.