- Anthropogenic CO₂ emissions are shifting the global climate equilibrium, causing widespread losses in biodiversity. Anthozoan cnidarians are some of the species most vulnerable to environmental change. Environmental stress causes corals and sea anemones to expel their endosymbiotic algae, which constitute a primary source of nutrition for some Anthozoa. Carbonic anhydrase (CA) proteins are important contributors to endosymbiont photosynthesis by regulating dissolved inorganic carbon forms within the cell, contributing directly to host nutrition. This study used real-time quantitative polymerase chain reaction to investigate the differential gene expression of four different CAs in the temperate sea anemone, Anthopleura elegantissima, across three symbiotic states: animals harboring the chlorophyte Elliptochloris marina, those harboring the dinoflagellate Brevolium muscatinei, and aposymbiotic animals. This investigation found that both symbiotic states upregulated CA expression compared to the aposymbiotic state. Of the four CAs investigated, two were found to be differentially expressed between B. muscatinei- and E. marina-harboring anemones. This research supports findings of symbiont-induced CA gene expression, contributing to the understanding of symbiont-host cell physiological interactions and nutrient flow. Such studies are crucial to understand adaptive potential in anthozoan and symbiont species.