The importance of ‘top-down’ regulation of assemblages by predators is well documented at a variety of spatial and temporal scales on rocky-shores. Predators have consumptive and non-consumptive impacts on their prey; however, much remains to be discovered about how climate change may affect predator-prey interactions and processes related to these interactions. We investigated the effect of predicted near-future ocean acidification on a molluscan defence mechanism: shell repair. We simulated non-consumptive damage by a durophagous (shell crushing) predator to 2 common intertidal gastropod species: Austrocochlea porcata and Subninella undulata. Our data show a stark contrast in the response of these 2 gastropods to simulated ocean acidification; A. porcata exhibited a depressed shell repair rate, compromised shell integrity and reduced condition. These 3 critical attributes for survival and protection against predators were all severely affected by ocean acidification. In contrast S. undulata was unaffected by ocean acidification. These results suggest that if atmospheric CO2 levels continue to rise, and ocean pH subsequently drops, then less resistant species such as A. porcata may face increased predation pressure and competition from more successful taxa within the same community. This could affect predator-prey relationships, with the potential to cascade through intertidal communities.