Regions Most at Risk from Ocean Acidification

Ocean acidification is a pervasive consequence of the rising carbon dioxide concentration in the atmosphere. When CO2 dissolves in seawater, it forms carbonic acid, which lowers pH and reduces the availability of carbonate ions necessary for calcifying organisms. This process affects coral reefs, shellfish, phytoplankton, and the broader marine food web, with cascading implications for coastal communities, fisheries, tourism, and cultural heritage. The vulnerability to ocean acidification is not uniform; it depends on a combination of natural factors, exposure to additional stressors, and the capacity to respond through adaptation, mitigation, and resilience-building. This article provides a region-by-region exploration of where ocean acidification poses the greatest risks today and into the near future, grounded in observed trends, projected scenarios, and socio-economic dependencies.

North Pacific regions

The North Pacific Ocean is a globally significant site for ocean acidification due to both high CO2 uptake and complex physical and biological processes. Regions along temperate to subarctic zones, including parts of the western United States, Hawaii, Alaska, and the coasts of Japan and the Russian Far East, show pronounced chemical changes in seawater. Upwelling systems, such as those off the coast of North America and parts of East Asia, bring deep, CO2-rich water to the surface, amplifying acidity and lowering calcium carbonate saturation states. These chemical conditions directly threaten shelled organisms like pteropods and juvenile mollusks, which serve as critical prey for larger predators and commercially important species. Coral reefs in this region face stress from coupled stressors, including warming temperatures and nutrient inputs from coastal development. The combination of high exposure to CO2, frequent upwelling, and environmental variability creates ecological and economic fragility for fisheries, aquaculture, and tourism that rely on healthy marine ecosystems.

In addition to direct chemical stress, the North Pacific supports many nearshore communities that rely on shellfish industries—oysters, clams, and mussels—that are particularly sensitive to acidified waters during larval stages. Indigenous communities and small-scale fisheries may be disproportionately affected due to stronger ties to local stocks and limited diversification options. Monitoring programs in this region emphasize carbonate chemistry, larval survival in acidified conditions, and the interaction of acidification with temperature stress. Adaptation strategies include selective breeding of resilient shellfish strains, improved hatchery practices, more selective harvest regulations to reduce stress on vulnerable cohorts, and diversified livelihoods that reduce dependence on a single stock.

North Atlantic regions

The North Atlantic exhibits noticeable acidification signaling, especially in coastal zones influenced by freshwater inputs and upwelling, including areas from the northeastern United States to Western Europe. The combination of cooling water masses, stratification patterns, and nutrient dynamics drives regional variability in pH and carbonate mineral saturation. In subpolar regions, the influx of carbon-rich deep waters can lower pH and aragonite saturation, while warmer, stratified surface layers in other seasons may modulate biological responses. The implications for calcifiers, such as oysters and pteropods, are pronounced in temperate estuaries and shelf ecosystems where shell-forming organisms are integral to food webs. Economically, northeastern Atlantic nations depend on fisheries, aquaculture, tourism, and ecosystem services that are sensitive to shifts in shellfish production and coral-like communities in cold-water reefs and rocky habitats.

Coastal infrastructure and hydrological changes influence the exposure of Atlantic coastal zones. Riverine inputs carry nutrients and organic matter, potentially altering local pH through microbial activity and benthic metabolism. In some regions, acidification interacts with warming seas and deoxygenation, creating compounded stress that can reduce the resilience of coastal ecosystems. Community adaptation hinges on monitoring carbonate chemistry, supporting shellfish hatcheries, and promoting diversified livelihoods that maintain resilience in the face of fluctuating marine productivity.

Tropical oceans and small island developing states (SIDS)

Tropical regions, including the Caribbean, the southeastern Pacific, the Indian Ocean, and parts of the western Pacific, face particular vulnerabilities due to the high metabolic rates of calcifying organisms in warmer waters and the ecological importance of coral reefs for shoreline protection, fisheries, and tourism. Coral reef systems in these regions are under multiple simultaneous pressures: warming-induced bleaching, nutrient enrichment from terrestrial runoff, pollution, overfishing, and disease dynamics. Ocean acidification compounds these stresses by reducing the aragonite and calcite saturation states that corals rely on to build and maintain their skeletons. For coral-dominated systems, even small decreases in saturation state can slow calcification, reduce reef accretion, and increase dissolution risk, which over time undermines the structural complexity that supports high biodiversity and the provisioning value of reefs.

Small Island Developing States (SIDS) are exceptionally vulnerable due to their geographic isolation, limited economic diversification, and heavy reliance on coastal and marine resources. In these economies, declines in shellfish production, degraded coral habitats, and reduced reef resilience translate into compromised fisheries, tourism revenue, and protection against storm surges. Local adaptation measures emphasize watershed management to reduce runoff, protected area networks to preserve resilient habitats, and community-led monitoring of carbonate chemistry and reef health. International support for climate finance, capacity-building, and technology transfer remains critical to enabling these regions to anticipate and respond to ocean acidification alongside broader climate impacts.

Coral reef regions around the world

Coral reef systems serve as keystone habitats in many coastal regions, housing immense biodiversity and supporting livelihoods through fisheries, tourism, and coastal protection. Ocean acidification directly threatens reef-building corals by reducing the rate of calcification and, in some cases, triggering net dissolution under low aragonite saturation states. The most vulnerable reefs tend to be those already stressed by warming, nutrient pollution, and sedimentation, where the added acidity pushes resilient species toward slower growth, reduced skeletal density, and increased vulnerability to disease. Regions with long-standing reef economies, such as the Caribbean, the Coral Triangle, and parts of the Western Indian Ocean, are at heightened risk because declines in reef health propagate through local food webs and shoreline protection networks.

Management strategies for coral reef regions emphasize local actions to reduce nutrients and sediments entering reef systems, establish marine protected areas, and promote restoration through coral gardening and assisted evolution where appropriate. The effectiveness of these strategies depends on integrating acidification monitoring with reef health indicators and ensuring that local stakeholders participate in decision-making processes. International collaboration supports research into regional calcification responses, resilience curves, and adaptive management approaches that can sustain reef services in the face of acidification and warming.

Regions with significant upwelling systems

Upwelling zones are characterized by recurrent supply of deep, cold, CO2-rich waters to surface layers. This phenomenon raises local acidity and lowers carbonate ion availability, particularly affecting marine life during early life stages and periods of strong biological demand. Prominent upwelling regions include the coasts of western North America, parts of western South America, Northwest Africa, and certain Eastern Boundary Current systems in the Atlantic and Indian Oceans. The ecological consequences include reduced calcification rates for shell-forming organisms, altered species composition, and potential mismatches between larval supply and food availability. Economically, upwelling zones often align with productive fisheries; thus, acidification can translate into reduced recruitment, shifts in species dominance, and the need for adaptive management of target species.

In response, monitoring programs focus on integrating physical upwelling signals with carbonate chemistry, while fishery management considers shifts in stock structure and vulnerability to environmental change. Adaptive strategies may involve diversifying target species, improving hatchery and aquaculture practices, and sustaining ecosystem-based management that buffers communities from abrupt changes in productivity.

Regions facing simultaneous warming and acidification

Regions experiencing concurrent ocean warming and acidification face compounded risks. Warmer waters can reduce the solubility of CO2, but they also intensify metabolic rates, respiration, and coral bleaching risk. In coastal zones where nutrient inputs and pollution are substantial, warming can exacerbate acidification effects by altering carbonate chemistry dynamics and reducing shell growth rates in mollusks and corals. These synergistic stressors can lead to sharper declines in calcifying organisms, with ripple effects across food webs, fisheries, and tourism-dependent economies.

Poleward margins, tropical-adjacent reefs, and temperate coasts with strong anthropogenic inputs are particularly sensitive. Mitigation and adaptation must address both climate and local stressors through strategies such as reducing nutrient runoff, implementing sustainable fisheries, protecting critical habitats, and supporting scientific monitoring that quantifies the interplay between temperature and pH changes.

Coastal communities and fisheries dependence

Coastal communities worldwide rely on marine resources for nutrition, livelihoods, and cultural identity. Regions with heavy dependence on shellfisheries, reef-associated species, and tourism-based economies are especially exposed to the economic shocks of acidification. Small-scale fishers, coastal towns with limited diversification, and communities vulnerable to weather extremes face elevated risks when acidification intersects with overfishing, habitat loss, and climate-driven disturbances.

Resilience-building in these regions involves diversifying income sources, developing climate-smart fisheries management, investing in early warning systems, and strengthening social networks to cope with variability. Education and outreach help communities understand carbonate chemistry and how local actions—such as reducing pollution and maintaining healthy estuaries—can influence coastal resilience.

Potential adaptation pathways

Across all regions, several adaptation pathways show promise in reducing vulnerability to ocean acidification. These include:

Reducing local stressors: Improving wastewater treatment, reducing agricultural runoff, and minimizing sedimentation to maintain healthier carbonate chemistry in nearshore waters.
Enhancing biodiversity and habitat complexity: Protecting and restoring oyster reefs, seagrass beds, and coral habitats to sustain ecological functions and improve resilience to pH changes.
Supporting resilient shellfish production: Developing selective breeding programs for acidification-tolerant shellfish and improving hatchery practices to increase survival rates under low pH conditions.
Diversifying livelihoods: Encouraging alternative income streams such as ecotourism, sustainable aquaculture, or value-added products to reduce dependence on a single resource.
Building informed governance: Implementing monitoring networks that track carbonate chemistry and biology, coupled with adaptive management frameworks that respond to early warning indicators.
Engaging communities: Involving local stakeholders in decision-making, education, and monitoring to build social capital and ensure alignment with cultural and economic needs.

Monitoring and data needs

Effective response to ocean acidification requires robust, regionalized monitoring of carbonate chemistry alongside ecological indicators. Data needs include long-term pH, total alkalinity, dissolved inorganic carbon, aragonite and calcite saturation states, and temperature. Biological indicators such as larval survival, growth rates of calcifiers, and coral health provide important context for translating chemical changes into ecological outcomes. Integrating satellite observations, autonomous sensors, and traditional monitoring networks enables a comprehensive view of acidification trends and their ecological and socio-economic consequences.

Regional collaboration and data-sharing platforms enhance the ability to compare impacts across biogeographic zones, identify hotspots of vulnerability, and tailor adaptation strategies to specific local contexts. Investment in capacity-building, especially in developing regions, supports sustained monitoring and better-informed policy decisions.

Economic and policy implications

Ocean acidification affects fisheries yields, aquaculture productivity, tourism, and coastal protection services. Regions with high dependence on shellfish industries or coral reef ecosystems face particular economic risks if acidification reduces recruitment or damages reef structure. Policy responses include integrating ocean acidification into climate adaptation plans, providing financial assistance for affected communities, and supporting research into mitigation and adaptation technologies. International cooperation and funding mechanisms can accelerate action, especially for regions with limited financial resources but high exposure.

Policy measures at national and local levels can address water quality, carbon emissions, and land-sea interfaces to reduce cumulative stress on marine ecosystems. Incorporating scientific findings into fisheries management, protected area design, and coastal zoning helps align economic incentives with ecological resilience.