In recent years much research has focussed on whether corals will be able to build their skeletons under predicted ocean acidification. One strategy corals may employ is changing the mineralogy of their skeletons from aragonite to the less soluble polymorph of calcium carbonate; calcite. Here we show that newly settled coral recruits are unable to produce calcite in their skeletons under near-future elevations in pCO₂, which may leave them more vulnerable to ocean acidification.