- Ocean acidification is caused by the dissolved carbon dioxide in the oceans lowering the amount of free carbonate ions. This is turn, affects the ability of calcifying organisms like mussels to build thick shells to protect against predation. Mussels are often preyed upon by both specialist crabs, like Red Rock crab (Cancer productus), and generalist crabs, like Kelp crab (Pugettia producta), but with limitations. This study considers the alterations to the limitations that are caused by thinning of mussel shells by ocean acidification. Crab preference to regular or thinned mussels was recorded during feeding trials. Times were taken for the time it took crabs to break the shells of both regular and thinned mussels. Kelp crab only ate the thinned mussels, meaning they could become a more frequent predator for mussels during ocean acidification conditions. Red Rock crab also preferred thinned mussels and it took them less time to break into them. The differences in feeding preference and breaking time for thinned and regular mussels were significant. This significance could help predict a shift in number of predators and feeding rate of crabs on mussels and other calcareous organisms caused by ocean acidification.