Ocean Acidification: A Growing Threat to Marine Ecosystems

The oceans play a fundamental role in regulating Earth's climate and supporting life. They absorb around 30% of the carbon dioxide (CO₂) produced by human activities, helping to slow global warming. However, as more CO₂ enters the ocean, seawater chemistry changes and leads to ocean acidification. Alongside ocean warming and sea level rise, acidification is one of the most serious consequences of climate change and poses a major threat to marine ecosystems. Ocean acidification occurs when atmospheric CO₂ dissolves in seawater and reacts with water to form carbonic acid. This process lowers the ocean's pH, making it more acidic. Since the Industrial Revolution, the average pH of surface ocean waters has decreased from about 8.2 to 8.1. Although this change may seem small, it represents an increase of approximately 30% in acidity. Scientists estimate that this decline is occurring much faster than any natural change recorded over millions of years, leaving many marine species with limited time to adapt. 

The organisms most vulnerable to acidification are those that rely on calcium carbonate to build shells and skeletons. These include corals, oysters, mussels, sea urchins, and microscopic plankton species that form the foundation of marine food webs. As acidity increases, carbonate ions become less available, making it harder for these organisms to grow and maintain their protective structures. Weaker shells and skeletons reduce survival rates and increase susceptibility to disease and predation. Coral reefs are among the ecosystems most affected by ocean acidification. They support a remarkable diversity of marine life and provide important ecosystem services, including coastal protection, tourism, and fisheries. Acidification slows coral growth and weakens reef structures, making them more vulnerable to erosion and environmental stress. Many studies suggest that, without significant reductions in greenhouse gas emissions, a large proportion of coral reefs may lose their ability to maintain positive growth by the end of the century. The effects of acidification are not limited to calcifying organisms. Research has shown that changes in seawater chemistry can affect the behaviour and development of some fish species. More acidic conditions may interfere with their ability to locate food, avoid predators, and navigate their environment. These changes can disrupt marine food webs and alter ecosystem balance, affecting species interactions throughout the ocean. Ocean acidification becomes even more damaging when combined with other climate-related pressures. Ocean warming is one of the most important of these. Rising sea temperatures have increased the frequency and intensity of marine heatwaves, which place additional stress on marine organisms and contribute to coral bleaching events. 

When warming and acidification occur simultaneously, many species become less resilient and less capable of adapting to environmental change. Sea level rise also contributes to the growing pressure on marine ecosystems. As oceans warm, seawater expands, and melting glaciers and ice sheets add more water to the oceans. Rising sea levels threaten coastal habitats such as mangroves, salt marshes, and seagrass meadows. These ecosystems are important carbon sinks, provide habitat for numerous species, and help protect coastlines from storms and erosion. Their degradation further reduces the resilience of coastal environments. Addressing ocean acidification requires tackling its root cause: excessive CO₂ emissions. Reducing greenhouse gas emissions is the most effective way to slow acidification and protect marine ecosystems in the long term. In addition, local conservation measures can strengthen ecosystem resilience. Marine protected areas, sustainable fisheries management, and the restoration of coastal habitats such as mangroves and seagrass beds can help marine species better cope with environmental change. Researchers are also exploring innovative solutions, including ocean alkalinity enhancement,although these approaches remain experimental. In conclusion, ocean acidification is a major environmental challenge that threatens marine biodiversity and ecosystem stability. Its impacts are intensified by ocean warming and sea level rise, creating a complex and interconnected problem. Reducing carbon emissions, protecting marine habitats, and supporting conservation efforts are essential steps to preserve the health of the oceans and ensure that they continue to support life and human well-being in the future.

Susana Lima, Associação Intercultural Para Todos