Ocean acidification, caused by human CO2 emissions, is harming abalone shells. Two abalone species were studied under different CO2 levels for a year. Both species showed shell damage, reduced hardness, and changes in shell structure. One species became more vulnerable to crushing force, while the other had decreased resistance. The shells also showed changes in chemical composition, making them less protective. Overall, abalone species are at risk in more acidic oceans, affecting their survival and ability to withstand predators and aquaculture stress.