Research Progress on the Formation Mechanisms of Ocean Acidification and Its Impacts on Marine Organisms and Ecosystems

Ocean acidification is one of the critical marine environmental issues under global climate change. As the ocean continuously absorbs anthropogenic carbon dioxide (CO₂), re-equilibration occurs in the seawater carbonate system, triggering a series of chemical shifts including declining pH, decreased carbonate-ion concentration and reduced calcium-carbonate saturation state. The magnitude of these changes is modulated by multiple factors such as temperature, salinity, ocean circulation, biogeochemical processes and terrestrial inputs, showing distinct regional heterogeneity. Ocean acidification affects marine organisms via pathways including acid-base balance disturbance, energy redistribution, ion regulation and calcification processes. Responses vary markedly across species and life-history stages. Calcifying organisms such as corals, shellfish, pteropods and calcifying algae have received substantial research attention, while non-calcifying organisms including phytoplankton, zooplankton and fish also exhibit physiological and ecological responses to varying degrees. Effects propagate from individuals and populations to drive community restructuring, altered food-web interactions, modified biogeochemical cycles and degraded ecosystem services. This paper systematically reviews the formation mechanisms and chemical characteristics of ocean acidification, as well as its impacts on representative marine organisms and ecosystems. Major advances regarding multi-stressor interactions, long-term acclimation and ecosystem-scale prediction are summarized. This work aims to support improved understanding of marine ecosystem responses and ecological risks under global change.