Explainer: Marine & freshwater biodiversity

Why It Matters

Monitored freshwater vertebrate populations have declined by 83% on average since 1970, and marine populations by 56%, making aquatic ecosystems the most rapidly degrading biomes on Earth (WWF Living Planet Report, 2024). These numbers are not abstract. The ocean economy generates an estimated $2.5 trillion in annual value through fisheries, coastal tourism, shipping, and marine biotechnology (OECD, 2024). Rivers and wetlands supply drinking water to over 4 billion people and sustain irrigated agriculture that produces 40% of the world's food. When aquatic biodiversity collapses, the economic and human consequences cascade through supply chains, insurance markets, and public health systems. For sustainability professionals, understanding the drivers of aquatic biodiversity loss, the frameworks designed to halt it, and the commercial dependencies at stake is now a strategic imperative rather than a conservation nicety.

Key Concepts

Marine biodiversity. The variety of life in ocean and coastal ecosystems, from phytoplankton and coral reefs to migratory fish stocks and deep-sea hydrothermal vent communities. The ocean harbors an estimated 700,000 to over 1 million species, of which roughly one-third remain undescribed (Census of Marine Life, updated 2025). Marine biodiversity underpins fisheries productivity, coastal protection, carbon sequestration (the ocean absorbs approximately 25% of anthropogenic CO2), and pharmaceutical discovery.

Freshwater biodiversity. The diversity of organisms in rivers, lakes, wetlands, and groundwater systems. Despite covering less than 1% of the Earth's surface, freshwater habitats support approximately 10% of all known species and one-third of all vertebrate species. Freshwater megafauna, including river dolphins, sturgeon, and large catfish, have declined by 94% since 1970 (He et al., 2024).

Blue economy. The sustainable use of ocean and freshwater resources for economic growth, improved livelihoods, and ecosystem health. The concept encompasses traditional sectors like fisheries and aquaculture alongside emerging industries such as offshore renewable energy, marine genetic resources, and blue carbon markets.

Marine protected areas (MPAs). Geographically defined zones where human activities are restricted to conserve marine ecosystems. The Kunming-Montreal Global Biodiversity Framework (GBF) set a target of protecting 30% of the ocean by 2030 (the "30x30" target). As of early 2026, approximately 8.3% of the global ocean is within designated MPAs, though only about 3% is fully or highly protected (Marine Conservation Institute, 2026).

Freshwater connectivity. The degree to which rivers, floodplains, and wetlands remain connected, allowing species migration, sediment transport, and nutrient cycling. Dams, weirs, and water abstraction have fragmented 63% of the world's longest rivers (Grill et al., updated 2025). Restoring connectivity is increasingly recognized as a priority for freshwater biodiversity recovery.

Environmental DNA (eDNA). DNA shed by organisms into water, sediment, or air that can be collected and sequenced to detect species presence without physical capture. eDNA sampling has transformed aquatic biodiversity monitoring, enabling rapid, non-invasive surveys that detect rare and elusive species at a fraction of the cost of traditional methods.

How It Works

Aquatic biodiversity loss is driven by five interconnected pressures, often described using the IPBES framework.

Habitat degradation and loss. Coastal development, bottom trawling, dredging, dam construction, wetland drainage, and land-use change in watersheds destroy or degrade the physical habitats that aquatic species depend on. Over 85% of global wetland area has been lost since 1700 (Ramsar Convention, 2024). Coral reefs, which support roughly 25% of marine species, have lost approximately 50% of their live coral cover since the 1950s.

Overexploitation. Overfishing is the primary driver of marine biodiversity decline. The FAO reports that 37.7% of assessed fish stocks are overfished, up from 10% in 1974 (FAO, 2024). Freshwater fisheries, which provide essential protein to hundreds of millions of people in low-income countries, face similar pressures from unsustainable harvest, illegal fishing, and bycatch.

Pollution. Nutrient runoff from agriculture creates oxygen-depleted dead zones; there are now over 700 identified globally. Plastic pollution introduces an estimated 11 million tonnes of plastic into the ocean annually, with microplastics detected in every ocean basin and freshwater system studied. Pharmaceutical residues, heavy metals, and pesticides further degrade water quality and disrupt reproductive and immune systems in aquatic organisms.

Climate change. Ocean warming, acidification, and deoxygenation are restructuring marine ecosystems. Sea surface temperatures reached record highs in 2024 and 2025, triggering the fourth global mass coral bleaching event (NOAA, 2025). Freshwater systems face altered precipitation patterns, glacial melt changes, and increased water temperatures that shift species ranges and reduce habitat suitability.

Invasive species. Non-native species introduced through ballast water discharge, aquaculture escapes, canal connections, and the aquarium trade displace native fauna. In the Great Lakes, invasive zebra and quagga mussels have fundamentally restructured the food web. In freshwater systems globally, invasive species are the leading cause of fish extinctions.

Protection and restoration frameworks. The GBF 30x30 target, the UN High Seas Treaty (BBNJ Agreement, adopted 2023), regional fisheries management organizations, river basin commissions, and national legislation form the governance architecture. Implementation depends on enforcement capacity, funding, and political will. The BBNJ Agreement, which enables the creation of MPAs on the high seas for the first time, entered the ratification phase in 2024 and by early 2026 had secured 112 signatories (UN DOALOS, 2026).

What's Working

MPA expansion and effectiveness. Several countries have made significant 30x30 commitments. The UK designated the Tristan da Cunha MPA covering 687,000 square kilometers, one of the largest no-take zones globally. Palau's National Marine Sanctuary protects 80% of its exclusive economic zone. Research published in Nature (Edgar et al., 2024) found that well-enforced, fully protected MPAs increase fish biomass by an average of 670% compared to unprotected areas.

Dam removal and river restoration. Europe removed a record 487 obsolete dams in 2024, led by France, Spain, and Sweden (Dam Removal Europe, 2025). In the United States, the removal of four dams on the Klamath River in 2024 reopened 600 kilometers of salmon habitat for the first time in over a century. These projects demonstrate that freshwater connectivity restoration can deliver rapid biodiversity gains.

eDNA monitoring at scale. NatureMetrics, a UK-based environmental biotechnology company, has deployed eDNA monitoring across 90 countries, enabling corporations and governments to assess aquatic biodiversity at scale. In Norway, eDNA surveys detected Atlantic salmon population trends 30 times faster than electrofishing methods (NatureMetrics, 2025). The technology is being integrated into regulatory compliance monitoring and biodiversity credit verification.

Blue carbon recognition. Mangroves, seagrass meadows, and tidal marshes sequester carbon at rates up to 10 times greater per unit area than terrestrial forests. Blue carbon projects are now eligible under major carbon registries including Verra and Gold Standard. Apple invested $50 million in mangrove restoration through its Restore Fund, generating both carbon credits and measurable biodiversity uplift.

What Isn't Working

MPA enforcement gaps. While MPA designation has increased, enforcement remains weak in many jurisdictions. A 2025 analysis by the Marine Conservation Institute found that only 36% of MPAs globally have management plans in place, and illegal, unreported, and unregulated (IUU) fishing continues inside many nominally protected areas. "Paper parks" that exist on maps but lack patrol capacity, monitoring, or community engagement provide minimal conservation benefit.

Freshwater neglect. Rivers, lakes, and wetlands receive disproportionately less conservation attention and funding than marine ecosystems. Only 16% of critical freshwater biodiversity areas are covered by protected areas, compared to 8.3% for oceans and 17% for terrestrial areas (IUCN, 2025). Major international frameworks, including the GBF, do not set separate targets for freshwater protection.

Fisheries management failures. Despite decades of regulatory effort, overfishing persists. Subsidies to the fishing industry totaled $35.4 billion globally in 2024, of which approximately $22 billion directly enhance fishing capacity and contribute to overfishing (Sumaila et al., 2024). The WTO Agreement on Fisheries Subsidies, adopted in 2022, has been ratified by fewer than half of WTO members.

Plastic treaty delays. Negotiations for a legally binding global plastics treaty under the UN Intergovernmental Negotiating Committee have stalled, with major petrochemical-producing nations resisting production caps. Without upstream production controls, downstream cleanup and recycling efforts cannot keep pace with the estimated 11 million tonnes of plastic entering the ocean each year.

Climate adaptation limits. Coral reefs, the most biodiverse marine ecosystems, face existential threats from warming. Even under the most optimistic climate scenarios (1.5 degrees Celsius warming), 70% to 90% of tropical reefs are projected to be lost. Assisted evolution, coral gardening, and marine heat-resistant strain development are being explored but remain at early experimental stages.

Key Players

Established Leaders

• IUCN — Maintains the Red List of Threatened Species and coordinates global freshwater and marine conservation programs.
• The Nature Conservancy (TNC) — Manages marine conservation projects in 30+ countries, including debt-for-nature swaps for ocean protection.
• WWF — Publishes the Living Planet Index and leads advocacy for 30x30 targets, freshwater restoration, and sustainable fisheries.
• FAO — Monitors global fish stock status and administers the Port State Measures Agreement against IUU fishing.

Emerging Startups

• NatureMetrics — eDNA-based aquatic biodiversity monitoring deployed across 90 countries for corporate and government clients.
• Coral Vita — Land-based coral farming startup in the Bahamas growing climate-resilient corals 50 times faster than natural growth rates.
• Upstream Tech — Remote sensing platform for watershed and wetland monitoring used by conservation organizations and water utilities.
• SafetyNet Technologies — Develops selective fishing technology (LED lights on nets) to reduce bycatch by up to 90% in target fisheries.

Key Investors/Funders

• Global Environment Facility (GEF) — Largest multilateral funder of marine and freshwater biodiversity projects, with $4 billion+ allocated since inception.
• Bloomberg Ocean Initiative — $300 million commitment to ocean conservation and sustainable fisheries.
• Bezos Earth Fund — Significant allocations to ocean and freshwater conservation within its $10 billion climate and nature commitment.
• Blue Nature Alliance — $125 million partnership (Conservation International, Pew, others) to protect 18 million square kilometers of ocean.

Sector-Specific KPI Benchmarks

Action Checklist

1. Map aquatic biodiversity dependencies. Use tools like ENCORE and IBAT to identify where your operations and supply chains intersect with critical marine and freshwater habitats.
2. Set science-based targets for nature. Align with the Science Based Targets Network (SBTN) freshwater and ocean guidance to establish measurable reduction targets for water pollution, abstraction, and habitat impact.
3. Source sustainable seafood. Transition procurement to MSC-certified wild-caught and ASC-certified farmed seafood. Require full vessel-to-plate traceability from suppliers.
4. Reduce plastic and nutrient pollution. Implement upstream plastic reduction strategies and upgrade wastewater treatment to minimize nutrient discharge into waterways.
5. Invest in blue carbon and freshwater restoration. Explore mangrove, seagrass, and wetland restoration projects that deliver both carbon sequestration and biodiversity co-benefits.
6. Deploy eDNA monitoring. Integrate eDNA surveys into environmental impact assessments and ongoing operational monitoring to establish biodiversity baselines and track trends.
7. Support policy advocacy. Advocate for ratification of the BBNJ Agreement, WTO fisheries subsidies reform, and a strong global plastics treaty.

FAQ

Why has freshwater biodiversity declined more than marine biodiversity? Freshwater systems are smaller, more fragmented, and more directly exposed to human pressures including damming, pollution, water abstraction, and land-use change in surrounding watersheds. Rivers and lakes concentrate impacts from entire drainage basins. Additionally, freshwater species often have limited dispersal ability compared to marine species, making them more vulnerable to local habitat loss and less able to shift ranges in response to environmental change.

What is the 30x30 target and is it on track? The 30x30 target, agreed under the Kunming-Montreal GBF in December 2022, commits nations to effectively conserve and manage 30% of the world's land and ocean areas by 2030. For oceans, coverage stood at approximately 8.3% in early 2026, meaning the target requires roughly quadrupling protected area coverage in four years. Progress is accelerating through high-seas MPA designations enabled by the BBNJ Agreement, but enforcement capacity and the quality of protection remain major concerns.

How does ocean warming affect biodiversity beyond coral reefs? Ocean warming is shifting species distributions poleward at an average rate of 70 kilometers per decade, disrupting food webs and fisheries that depend on historical species assemblages. Deoxygenation, driven by warming and nutrient loading, is expanding oxygen minimum zones where most marine life cannot survive. Acidification, caused by CO2 absorption, weakens the shells and skeletons of calcifying organisms from pteropods to oysters. Together, these stressors are projected to reduce marine animal biomass by 5% to 17% per degree of warming (Lotze et al., 2024).

Can aquaculture help relieve pressure on wild fish stocks? Aquaculture now produces more fish for human consumption than wild capture and can reduce pressure on overfished stocks if managed sustainably. However, poorly managed aquaculture introduces its own biodiversity risks, including habitat conversion (especially mangrove destruction for shrimp farming), nutrient pollution, disease transmission to wild populations, and reliance on wild-caught fish for feed. ASC certification and improvements in feed technology (insect meal, algae-based feeds) are helping address these concerns, but the sector's growth must be guided by spatial planning and strong environmental standards.

What role does eDNA play in aquatic conservation? Environmental DNA analysis allows scientists and practitioners to detect species from water samples without physically observing or capturing organisms. A single liter of water can reveal the presence of hundreds of species. This makes eDNA particularly valuable for monitoring elusive, rare, or nocturnal aquatic species, tracking invasive species, verifying restoration outcomes, and conducting rapid biodiversity assessments across large areas. Costs have fallen to roughly $50 to $150 per sample, making eDNA increasingly accessible for routine corporate and regulatory monitoring.

Sources

• WWF. (2024). Living Planet Report 2024: A System in Peril. World Wildlife Fund.
• OECD. (2024). The Ocean Economy in 2030: Opportunities and Challenges. Organisation for Economic Co-operation and Development.
• FAO. (2024). The State of World Fisheries and Aquaculture 2024. Food and Agriculture Organization of the United Nations.
• NOAA. (2025). Global Coral Bleaching Monitoring: Fourth Global Event Summary. National Oceanic and Atmospheric Administration.
• Marine Conservation Institute. (2026). Marine Protection Atlas: Global MPA Coverage and Effectiveness. Marine Conservation Institute.
• He, F. et al. (2024). Global Decline of Freshwater Megafauna. Global Change Biology.
• Edgar, G.J. et al. (2024). Reef Fish Biomass Recovery in Marine Reserves. Nature.
• Dam Removal Europe. (2025). Dam Removal Progress Report 2024. Dam Removal Europe.
• NatureMetrics. (2025). eDNA Monitoring at Scale: Global Deployment and Impact Assessment. NatureMetrics Ltd.
• Sumaila, U.R. et al. (2024). Updated Estimates of Global Fisheries Subsidies. Marine Policy.
• Lotze, H.K. et al. (2024). Projected Changes in Marine Animal Biomass Under Climate Warming. Science.
• UN DOALOS. (2026). Status of the BBNJ Agreement: Signatories and Ratifications. United Nations Division for Ocean Affairs and the Law of the Sea.