The hidden threat to marine ecosystems
Ocean acidification occurs when carbon dioxide (CO2) from the atmosphere dissolves in seawater, forming carbonic acid. This process lowers the pH of ocean water, making it more acidic. Since the Industrial Revolution, the ocean's pH has decreased by approximately 0.1 units, representing a 30% increase in acidity.
The ocean has absorbed about 30% of human-produced CO2 emissions, acting as a crucial buffer against climate change. However, this service comes at a cost to marine ecosystems. The rate of acidification is unprecedented in Earth's history, occurring 10 times faster than any known natural change.
The pH scale measures acidity from 0 (most acidic) to 14 (most basic), with 7 being neutral. Ocean pH has historically been around 8.2, slightly basic. Current levels are around 8.1, and projections suggest pH could drop to 7.8 by 2100 under high-emission scenarios. While this may seem like a small change, the pH scale is logarithmic, meaning each unit represents a 10-fold change in acidity.
Acidification affects marine organisms in multiple ways, with calcifying species being particularly vulnerable. As acidity increases, the concentration of carbonate ions decreases, making it harder for organisms to build and maintain calcium carbonate shells and skeletons.
Corals build their skeletons from calcium carbonate, a process that becomes increasingly difficult as ocean acidity rises. Acidification slows coral growth, weakens coral structures, and makes reefs more vulnerable to erosion. Combined with warming waters, acidification poses a severe threat to coral reef ecosystems worldwide.
Oysters, clams, mussels, and other shellfish struggle to form shells in acidic conditions. Larval stages are particularly vulnerable, with many species experiencing high mortality rates. This threatens both wild populations and aquaculture operations, which are important sources of food and livelihoods.
Many plankton species, including pteropods (sea butterflies) and coccolithophores, build calcium carbonate shells. These tiny organisms form the base of marine food webs, and their decline could have cascading effects throughout ocean ecosystems. Pteropods are already showing signs of shell dissolution in some regions.
Acidification can affect fish behavior, including their ability to detect predators, find food, and navigate. Studies have shown that elevated CO2 levels can impair sensory systems and increase risk-taking behavior, potentially reducing survival rates. Some fish species may also experience reduced growth and reproduction.
The impacts of acidification extend beyond individual species to affect entire ecosystems. Changes in species composition, altered food webs, and reduced biodiversity can fundamentally transform marine ecosystems. Coral reefs, which support immense biodiversity, are particularly at risk.
The loss of calcifying organisms can reduce the structural complexity of habitats, affecting species that depend on these structures for shelter and food. This can lead to reduced biodiversity and ecosystem productivity, with consequences for fisheries and coastal protection.
Acidification is not uniform across the ocean. Some regions, particularly upwelling areas where deep, CO2-rich water rises to the surface, experience more severe acidification. The Arctic and Southern Oceans are also particularly vulnerable due to cold water's ability to hold more CO2.
Coastal areas can experience even more extreme acidification due to local factors such as nutrient pollution, which can enhance acidification through biological processes. Understanding these regional variations is important for developing targeted adaptation strategies.
The most effective solution is reducing CO2 emissions. Limiting global warming to 1.5°C or 2°C above pre-industrial levels, as outlined in the Paris Agreement, would significantly reduce acidification. Rapid transition to renewable energy and carbon capture technologies are essential.
Even with aggressive emission reductions, some acidification is inevitable due to CO2 already in the atmosphere. However, reducing future emissions can prevent the most severe impacts and give marine ecosystems more time to adapt.
Reducing other stressors on marine ecosystems can help them better cope with acidification. This includes reducing pollution, protecting habitats, and managing fisheries sustainably. Ecosystems that are healthy and diverse are generally more resilient to acidification.
Marine protected areas can provide refuges where ecosystems can adapt with reduced human pressure. Protecting biodiversity helps maintain ecosystem function even as conditions change.
Comprehensive monitoring programs track acidification trends and impacts, providing essential data for understanding and responding to changes. Research into acidification-resistant species and adaptation mechanisms can inform conservation priorities.
Long-term monitoring helps identify early warning signs and track the effectiveness of mitigation efforts. Citizen science programs can expand monitoring coverage and engage communities in ocean conservation.
Some research suggests that selective breeding could help develop acidification-resistant strains of commercially important species like oysters. However, this approach has limitations and must be carefully evaluated for ecological and ethical implications.
Natural adaptation may occur over time, but the rapid rate of acidification may outpace evolutionary responses. Protecting genetic diversity gives species more options for adaptation.
SeaSave Collective supports research on ocean acidification impacts and advocates for ambitious emission reduction policies. We work to raise awareness about this "other CO2 problem" and its consequences for marine ecosystems.
Our programs include supporting monitoring networks, facilitating research on acidification-resistant species, and promoting policies that reduce CO2 emissions. We work with aquaculture operations to develop adaptation strategies and support marine protected areas that can serve as refuges.
Addressing ocean acidification requires global action to reduce CO2 emissions. By working together—scientists, policymakers, businesses, and citizens—we can limit acidification and protect marine ecosystems for future generations. The time for action is now.