Ocean acidification reduces the ability of corals to build and maintain reef structures by changing seawater chemistry and disrupting biological processes. Ken Caldeira at Carnegie Institution for Science explains that the ocean absorbs a large fraction of anthropogenic carbon dioxide emissions, which reacts with seawater to form carbonic acid. This process increases hydrogen ion concentration and lowers carbonate ion availability, the molecules that many marine organisms need to form calcium carbonate skeletons. The National Oceanic and Atmospheric Administration reports that these chemical shifts lower the saturation state of aragonite, the form of calcium carbonate used by reef-building corals, directly affecting calcification rates and skeletal strength.
Mechanisms: how CO2 alters seawater chemistry
Reduced carbonate availability makes it more difficult for corals to deposit skeletal material and for young corals to establish themselves. Ove Hoegh-Guldberg at the University of Queensland has documented that under lowered aragonite saturation states coral calcification slows and skeletons become thinner and more porous. That weakened skeletal framework increases susceptibility to bioerosion and physical breakage during storms. Acidified conditions also interfere with coral larval development and settlement, reducing recruitment and the natural recovery capacity of reefs after disturbance.
Ecological, cultural, and socioeconomic consequences
The ecological consequences cascade through reef ecosystems. As corals calcify less and mortality increases, three-dimensional reef complexity declines, reducing habitat for fishes and invertebrates and lowering biodiversity. The Intergovernmental Panel on Climate Change and NOAA emphasize that ocean acidification interacts with warming, pollution, and overfishing to exacerbate coral bleaching and disease, accelerating shifts from coral-dominated to algae-dominated states. For human communities, these ecological shifts undermine fisheries, tourism, and coastal protection. Many coastal and island societies, especially in the Pacific and the Coral Triangle region, have cultural practices and food systems tied to healthy reefs; loss of reef function therefore carries cultural and territorial consequences that extend beyond economic metrics.
Causes, mitigation, and resilience
The primary cause of modern ocean acidification is increased atmospheric carbon dioxide from fossil fuel combustion and land-use change. Scientific consensus from leading researchers and agencies indicates that reducing global CO2 emissions is the essential action to halt and eventually reverse ongoing acidification. Local management also matters: reducing nutrient pollution, protecting herbivores, and controlling overfishing can improve reef resilience and enable natural recovery under moderate acidification. Research led by Ove Hoegh-Guldberg and others demonstrates that combined global and local interventions increase the likelihood that reefs can persist in a changing ocean.
Understanding and addressing ocean acidification requires integrating chemical monitoring, ecological research, and the perspectives of reef-dependent communities. Evidence from researchers such as Ken Caldeira at Carnegie Institution for Science and institutions like the National Oceanic and Atmospheric Administration supports targeted emission reductions and locally tailored stewardship as the most credible path to protect coral reef health.