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How can ocean acidification harm coral reefs and sea urchins?

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Illustration of various geoengineering techniques to address climate change, including carbon capture and storage methods like artificial trees, industrial scrubbers, and deep ocean CO2 storage, as well as solar reflectance strategies such as sulfur aerosols, reflective crops, cloud whitening, and orbital mirrors. The scene shows these interventions applied to land, sea, and atmosphere, with labeled features explaining each process. — Geoengineering Various geoengineering proposals designed to increase solar reflectance or capture and store carbon.

Ocean acidification harms coral reefs and sea urchins primarily by reducing the availability of carbonate ions in seawater, which these organisms require to build and maintain their calcium carbonate skeletons and shells.12

As atmospheric carbon dioxide is absorbed by the oceans, it reacts with water to form carbonic acid, which lowers the pH of the seawater and consumes carbonate ions. The specific impacts include:12

Coral Reefs: Reduced carbonate concentrations hinder the ability of corals to grow and maintain their structures. If acidification intensifies, these vital ecosystems—which serve as centers of biodiversity—face the risk of decline or even disappearance.1
Sea Urchins: Research indicates that sea urchin larvae develop smaller skeletons under high-acidity conditions. This reduction in size can make them more vulnerable to predators that would otherwise avoid them.1

Beyond these structural challenges, the physiological stress caused by increased acidity can impair growth, reproduction, and overall survival, potentially threatening the stability of entire marine food chains.1