<div>In summary, we did not detect a significant impact of ocean acidification on areal symbiont densities in the coral Pocillopora damicornis, contrasting with the findings of numerous other studies. However, ocean acidification did impact upon respiration and photosynthesis under some (but not all) standardisations. Hence, whilst we did not find direct evidence that ocean acidification may cause changes in symbiont densities and potentially coral bleaching, it is clear that it had an impact on the photophysiology of the Symbiodinium cells. At crucial moments during temperature or light stress, the possibility remains open that the changes in symbiont photophysiology caused by ocean acidification may directly impact upon the process of physiological process of coral bleaching. <br></div>