Ocean acidification is the gradual decrease in the ocean’s pH level, primarily resulting from the absorption of carbon dioxide (CO2) from the atmosphere over an extended period. In the past century or so, seawater has become about 30% more acidic, shifting from its traditionally near-neutral pH of around 8.

Process of Ocean Acidification

• Carbon Dioxide (CO2) Absorption: Excess CO2 is released into the atmosphere mainly from human activities, such as burning fossil fuels (coal, oil, and natural gas) and deforestation. These activities significantly increase CO2 levels in the atmosphere.
• Transport to Oceans: Rainwater containing dissolved CO2 and carbonic acid falls onto the Earth’s surface, including the oceans. This water carries the excess CO2 from the atmosphere into the oceans.
• Atmospheric CO2 Dissolution: Once released into the atmosphere, CO2 molecules dissolve in rainwater and form carbonic acid (H2CO3). This carbonic acid is a weak acid but plays a crucial role in the acidification process.
• Carbonic Acid Ionization: In seawater, carbonic acid molecules dissociate into bicarbonate ions (HCO3-) and hydrogen ions (H+). This process increases the concentration of hydrogen ions in the water, lowering its pH level.
• pH Reduction: The increase in hydrogen ions makes seawater more acidic, causing a decrease in its pH level. Ocean pH is measured on a logarithmic scale, so even small changes represent significant shifts in acidity.

Consequences of Ocean Acidification for Marine Ecosystems

• Coral Reef Decline: The reduced pH levels hinder the ability of corals to form their calcium carbonate skeletons, leading to weaker and slower growth. For example, since 1950, ocean acidification has resulted in a roughly 13% decrease in the skeletal density of massive Porites corals within the Great Barrier Reef.
• Disrupted Food Chains: Ocean acidification can disrupt marine food chains by altering the availability and distribution of prey and predators. For example, alterations in pH levels can affect the sensory mechanisms of fish larvae, potentially hindering their ability to detect and evade predators,
• Impaired Reproduction and Population Decline: Ocean acidification poses a threat to marine species by potentially reducing their reproductive success, which, in turn, can lead to declining population sizes. For example, increased acidity can result in the improper development of sea urchin and oyster larvae, impacting their ability to reproduce and sustain their populations.
• Shift in Species Dominance and Biodiversity Loss: Ocean acidification’s regional impact on marine ecosystems varies, causing shifts in species dominance and significant biodiversity loss. For example, in Papua New Guinea, carbon dioxide seeps replaced branching corals with boulder forms and, in some areas, entirely replaced corals with sand, rubble, and algae beds.
• Increased Vulnerability to Other Stressors: Weakened by acidification, marine organisms become more susceptible to other stressors like rising ocean temperatures and pollution, intensifying the challenges they face.
• Cascading Effects of Vulnerable Ecosystem Decline: As vulnerable ecosystems decline due to ocean acidification, the associated species that depend on these habitats for shelter and sustenance risk losing their homes, which can have cascading effects throughout the food web. For instance, the complete depletion of coral reefs can result in the loss of up to 25% of marine species dependent on these delicate ecosystems.

Ocean acidification presents a significant peril to marine ecosystems, with the capacity to trigger cascading effects that disrupt the delicate balance of marine life. By recognizing the issue’s severity, promoting global cooperation, adopting sustainable practices, and advancing research to curb carbon emissions and their impacts, we can strive to preserve the delicate balance of our oceans and ensure their vitality for generations to come.