Light is the most abundant resource within the nutrient poor waters surrounding coral reefs. Consequently, both photoacclimation and photoadaptation of the coral host and the symbiotic microalgae, Symbiodinium, play a crucial role in ensuring coral success. This thesis systematically examined responses (phenotypic and genotypic) of hermatypic corals across environmental gradients by 1) characterising variability between different isolated Symbiodinium types under different light regimes, 2) examining the role of the host in photoacclimation using laboratory and in situ transplant experiments, and 3) assessing photoacclimation and photoadaptation strategies in four key coral species across habitats to determine key drivers of coral distribution. Future studies will be able to build upon observations in this thesis to describe how the phenotypic (acclimatory) and genotypic (adaptive) contribution of both holobiont fractions determine coral distribution. Ultimately, this will contribute towards a better understanding of the form (and in turn the function) of future coral reefs.