The ocean has always seemed immeasurably vast and unchanging, a realm so deep and ancient that human activity could hardly make a dent in its rhythms. Scientists now warn that this assumption is outdated. While it might be calming to stand on a beach and watch the waves roll in, little do we realise that a quiet change is taking place within the familiar-looking ocean. The water is slowly turning more acidic, almost like a few extra drops of lemon in a glass of water. We cannot see it, but marine life feels it every day. For a country like India, where millions depend on the sea for food and income, this invisible change carries real consequences.
Across the world’s seas, an invisible chemical shift is underway, altering marine life, coastal economies, and the future stability of many communities. This phenomenon, known as ocean acidification, is sometimes described as “the osteoporosis of the sea”, a quiet crisis unfolding beneath the waves and often overshadowed by the more visible impacts of climate change.
Ocean acidification is the slow fall in ocean pH caused by rising carbon dioxide in the air. The ocean absorbs about one third of the carbon we release when we burn coal, oil, and gas. When this carbon mixes with seawater, it forms carbonic acid. This makes the water more acidic and reduces carbonate ions needed by many marine creatures to build shells and skeletons.
Since the start of the Industrial Revolution, the ocean has become almost one third more acidic. Scientists warn that this trend will continue unless emissions fall sharply. Corals grow more slowly. Shellfish struggle to form shells. Some species change their behaviour or lose their ability to sense predators.
A new scientific review from researchers at Amrita Vishwa Vidyapeetham shows ocean acidification may be just as disruptive, and in some regions even more immediate, than rising temperatures or sea level rise. Its consequences could reverberate for centuries.
As atmospheric carbon dioxide rises due to fossil fuel use and deforestation, the ocean absorbs nearly 30 percent of this CO₂. Once dissolved, it forms carbonic acid, which lowers seawater pH and reduces carbonate ions that many organisms use to create shells, skeletons, and reefs.
Since the Industrial Revolution, ocean pH has fallen by 0.1 units, making the water about 30 percent more acidic. Though the numerical shift appears small, the pH scale is logarithmic, meaning the chemical change is significant. Without major emission reductions, ocean pH could decline by another 0.3 to 0.4 units by 2100. For corals, molluscs, plankton, and many other species, this change threatens survival.
Countries like the United States, Canada, Norway, and Australia have invested in monitoring programmes that track long term changes in pH, carbonate chemistry, and ocean health. They study how OA affects corals, shellfish, plankton, and fisheries and experiment with ways to build resilience, such as restoring seagrass beds and mangroves, breeding hardy shellfish, and protecting reef systems.
Some regions have already experienced losses. Coral calcification on the Great Barrier Reef has dropped sharply. Shellfish hatcheries in the Pacific North west of the United States have recorded major seedling deaths during high CO₂ events. In the Mediterranean Sea, falling carbonate levels affect molluscs that support fisheries and tourism. These lessons show that OA is not a distant future threat. It is already altering ecosystems, industries, and coastal livelihoods.
India has one of the longest coastlines in Asia, and millions of people depend on the sea for income. Almost seventy percent of fishing households live near or below the poverty line, making adaptation difficult.
India’s four major coral reef systems already face temperature-related bleaching. Acidification slows coral growth and weakens reef structures, affecting shore protection, fish nurseries, and tourism.
India also has a large aquaculture sector that relies on species sensitive to pH and carbonate levels. Molluscs, crustaceans, and some finfish can face growth and survival challenges in more acidic waters. Yet India’s research output on OA remains low and scattered. Most studies focus on coral bleaching or warming. There is no national OA monitoring network, and only a few long-term coastal observations exist.
The review notes that India contributes only a fraction of global OA literature and lacks coordinated national monitoring. With 67.3 percent of India’s fishing households living at or below the poverty line, disruption to marine resources could undermine livelihoods, nutrition, and coastal stability. Without long-term pH and carbonate chemistry data, policymakers lack the scientific foundation needed to anticipate risks or design adaptation measures.
India’s vulnerability is shaped by the contrasting behaviour of the Arabian Sea and Bay of Bengal. The Arabian Sea is influenced by coastal upwelling, which brings CO₂ rich deep waters to the surface. Combined with rising sea surface temperatures, this intensifies acidification and reduces the ocean’s ability to absorb more CO₂. Trends suggest a surface pH decline of about 0.015 units per decade. Experiments on sea urchins show that exposure to acidic conditions alters skeletal structure and survivability.
The Bay of Bengal faces a different challenge. Massive freshwater input from rivers lowers alkalinity and reduces the ocean’s natural buffering capacity. Stratification traps CO₂ rich water near the surface, while aerosol pollution accelerates acidification. Researchers have recorded local pH declines of roughly 0.003 units per year. Climate oscillations such as the Indian Ocean Dipole further modify water chemistry by altering rainfall and river discharge patterns. Acidification interacts with warming, deoxygenation, and nutrient loading from agriculture and sewage.
Studies show that both the Arabian Sea and the Bay of Bengal are experiencing a steady drop in surface pH. Model studies estimate a pH drop of about point zero one five units per decade in the Arabian Sea. The Bay of Bengal shows slightly slower trends but strong seasonal swings. During years of low river flow, less dilution and more upwelling cause sharper increases in acidity.
Laboratory experiments on sea urchins, oysters, and corals from Indian waters show that long exposures to lower pH reduce skeletal strength, change metabolism, and affect reproductive success. These findings show the importance of monitoring coastal acidification and understanding how pollution and nutrient loads interact with global CO₂ trends.
The impacts extend beyond reefs to species that sustain coastal fisheries. Shell building organisms grow thinner shells. Some crustaceans experience metabolic stress. Fish may face sensory and behavioural changes. Phytoplankton, the base of marine food webs, can shift in composition under acidified conditions, affecting fisheries. For millions of Indian fishers, especially small scale communities, even small drops in fisheries productivity could cause economic and nutritional disruptions.
A strong national response can help protect ecosystems and coastal economies. A simple and practical framework should include:
1. Build a national OA monitoring network
Install low-cost pH sensors, CO₂ loggers, and carbonate chemistry stations at strategic points along the coast. Connect them to regional observing systems.
2. Strengthen research and collaboration
Support studies that link OA with warming, eutrophication, plastics, and river discharge. Encourage universities, IITs, research institutes, and state fisheries departments to work together.
3. Protect and restore natural buffers
Mangroves, seagrass meadows, and salt marshes can absorb CO₂ and improve local water chemistry. Protecting them supports ecosystems and communities.
4. Support small-scale fishers and aquaculture
Provide early warning information, training, and financial support. Promote hardy species and adaptive practices.
5. Integrate OA into policy and planning
Include OA in coastal zone management, fisheries policy, climate action strategies, and blue economy roadmaps. Align with SDG 14.3.
Ocean acidification is a slow and silent change, but its impact can be sweeping. For a country with deep cultural, ecological, and economic ties to the sea, understanding and responding to OA is essential. Strengthening science, empowering communities, and restoring marine ecosystems can help build resilience. The sooner we act, the better chance we have to protect life below water and the people who depend on it.
Citation:
Vysakh S, Sabarinath S, Shijin Ameri, Puneeta Pandey, Akshay Satish, Vijai Dharmamony, Maneesha Vinodini Ramesh, Ocean Acidification: Global Perspectives and India's Path Forward, iScience, 2025.