Ocean warming is often implicated in the widespread demise of coral reefs, as high temperatures can lead to a breakdown of the relationship between coral hosts and their algal symbionts. However, recent research has revealed that the effects of warming on corals of the same species may vary widely depending on their thermal history. Specifically, corals from nearshore habitats, which experience relatively extreme daily and seasonal temperature fluctuations, have demonstrated higher tolerance than those which experience more thermally stable conditions. Importantly, this variation in thermal tolerance has been shown to be heritable, implying that genetic linkage between resilient nearshore and sensitive forereef populations could foster reef-scale adaptation to warming. Here, we use 2bRAD sequencing to explore the population genomics of the massive starlet coral, Siderastrea siderea, throughout the Belize Barrier Reef. 142 colonies of S. siderea were sampled across five pairs of nearshore and forereef sites. These sites were intentionally selected based on their distinct thermal characteristics, where nearshore sites experience both warmer and more variable temperature conditions than those on the forereef. However, we find that populations on this reef are not in fact differentiated based on these thermal regimes, but rather by light availability. This result suggests that for S. siderea, one of the few species that has shown resilience to ocean warming trends, water quality may in fact be a more important selective force than temperature variation, at least at the regional scale.