In the context of ocean warming, coral bleaching provides a window of opportunity for the establishment of novel symbiont associations that may change the symbiont community trajectory, and consequently, host fitness. Recent studies have leveraged this concept to enhance coral thermal resilience through introduction of heat-evolved Symbiodiniaceae into bleached corals. However, the capacity for corals to establish and maintain symbiosis with heat-evolved strains when in competition with other strains remains to be seen. Here, we explore symbiont acquisition and proliferation in adult corals when experimentally inoculated with a mixed assemblage of Symbiodiniaceae. Following a chemical bleaching treatment (DCMU and menthol), fragments of two horizontally transmitting corals, Platygyra daedalea and Galaxea fascicularis, were subjected to one of four Symbiodiniaceae cross-paired mixtures: wild-type Cladocopium + wild-type Durusdinium, wild-type Cladocopium + heat-evolved Durusdinium, heat-evolved Cladocopium + wild-type Durusdinium, or heat-evolved Cladocopium + heat-evolved Durusdinium. Symbiont acquisition success and proliferation of strains within each combination was measured over time using quantitative genetic assays. Findings from this study will provide insight into the mechanisms of Symbiodiniaceae community organization and have implications for optimization of Symbiodinaiceae directed evolution as an intervention strategy to improve host fitness.