Organismal behavior is influenced by the surrounding environment, an extent of which is modulated by endogenous biological clocks. These timekeeping systems maintain synchrony between internal and external environments, allowing organisms to anticipate and acclimate to future conditions. Broadcast spawning corals rely on changes in seasonal temperature, lunar phase and time of day to synchronize spawning. Responses to environmental rhythms in coral are well studied, but rhythms in their symbiotic algae are not. We investigate gene expression profiles of Cladocopium goreaui, the algal symbiont hosted by the coral Acropora millepora, across temperatures, lunar phases and times of day to understand how these rhythms interact to influence algae in-hospite. RNA from the holobiont was sampled over 24-hr periods across a full lunar cycle at two seasonal temperatures. Symbiont gene expression was quantified and networks of co-expressed genes were correlated with environmental rhythms and temperature treatments. Preliminary results show that temperature, lunar phase, specifically the full moon phase, and coral host genotype were more influential in modulating gene expression than time, though analyses are ongoing. A previous study investigating the influence of these three rhythms on the A. millepora hosts showed specific genes and core processes were differentially impacted by diurnal-temperature, lunar-temperature and diurnal-lunar interactions. Together, this research can determine the extent coral hosts and their algal symbionts co-regulate one another’s biological timekeeping on the genomic level.