Rising CO2 dissolves in seawater to form carbonic acid, lowering ocean pH. This chemical change impairs the physiology, behaviour, and survival of vast numbers of marine animals.
Ocean acidification causes welfare harm through multiple pathways. Fish in acidic conditions show impaired sensory function — they cannot detect predators or navigate effectively, increasing predation and disorientation stress. Calcifying animals (shellfish, corals, echinoderms) experience shell dissolution and growth impairment. Larvae and juveniles are most sensitive, with acidification causing developmental abnormalities and mortality. The welfare scale is effectively unlimited — acidification affects every ocean-dwelling animal on Earth. Carbon emission reduction is the only effective intervention.