This study investigated the possible effects of ocean acidification on the calcareous skeleton of a Mediterranena bryozoan by transplanting live and dead colonies into an area of natural volcanic carbon dioxide vents in the Tyrrhenian Sea, Italy. Colonies remained alive at the below-normal and acidic pH sites during the 45-day experiment, but corrosion was very striking after 128 days, with colonies from the acidic site showing significant loss of skeleton. The findings suggest that bryozoans with magnesium calcite skeletons may have difficulty surviving predicted ocean acidification.