Ocean Acidification Impacts on Marine and Coral Reef Ecosystems

Ocean acidification driven by rising atmospheric CO₂ reduces seawater pH and alters the carbonate system, with widespread consequences for marine organisms and ecosystems. Lower pH and reduced carbonate ion availability impair calcification in shell-forming plankton, molluscs, echinoderms and corals, compromising skeletal growth and structural integrity. Coral reefs, already threatened by warming, face further stress as diminished carbonate saturation states slow reef accretion and weaken habitat complexity. Sub-lethal effects include altered physiology, reduced fertility and behavioural changes in fish, with cascading impacts on food webs and ecosystem services such as fisheries and coastal protection. Spatial and temporal variability in acidification exposure—driven by coastal upwelling, biological metabolism and hydrodynamics—creates mosaics of high and low pH that influence community resilience and refugia potential. Multifactorial interactions with warming, deoxygenation and nutrient loading intensify biological impacts and challenge predictive models. Recent research emphasises the need to integrate high-resolution observing networks, long-term data compilations and multifactorial experiments to resolve organismal responses across life stages, quantify ecosystem-scale feedbacks and inform adaptive management strategies to preserve biodiversity and ecosystem function under future acidified oceans.

Research from Nature Portfolio

Recent studies have revealed persistent spatial heterogeneity in acidification exposure along coastal upwelling systems, demonstrating that hotspots of low pH can persist for large fractions of the growing season and expose calcifiers to some of the most acidic nearshore waters documented. Conversely, adjacent refugia with relatively stable and higher pH have been identified, highlighting opportunities for local conservation measures and spatial management to buffer vulnerable populations. Advances in autonomous sensor networks have enabled high-resolution mapping of coastal carbonate chemistry, underlining the importance of mesoscale processes in driving nearshore variability and informing targeted interventions to protect critical habitats under future acidification scenarios.

Ocean Acidification Impacts on Marine and Coral Reef Ecosystems publication trend

The graph below shows the total number of articles in ocean acidification impacts on marine and coral reef ecosystems across all publications each year (not limited to Nature Index journals).

Technical terms

pH: Logarithmic measure of hydrogen ion concentration in seawater, indicating acidity.

Carbonate ion concentration: Availability of CO₃²⁻ ions, essential for calcium carbonate formation in marine organisms.

Aragonite saturation state (Ωarag): Ratio of seawater carbonate ion concentration to the amount needed for aragonite to be in equilibrium; values below 1 indicate risk of dissolution.

Calcification: Biological process by which organisms deposit calcium carbonate to build shells and skeletons.

Upwelling: Oceanographic process that brings deep, cold, CO₂-rich waters to the surface, exacerbating local acidification.

References

1. An update of data compilation on the biological response to ocean acidification and overview of the OA-ICC data portal. Earth System Science Data (2024).
2. Persistent spatial structuring of coastal ocean acidification in the California Current System. Scientific Reports (2017).
3. Meta‐analysis reveals complex marine biological responses to the interactive effects of ocean acidification and warming. Ecology and Evolution (2013).
4. Photosynthetic activity buffers ocean acidification in seagrass meadows. Biogeosciences (2014).
5. High temporal and spatial variability of dissolved oxygen and pH in a nearshore California kelp forest. Biogeosciences (2012).