In the past decades climate change and other anthropogenic stress factors have led to the decline of coral reefs all over the globe. It became evident that corals are highly sensitive to thermal stress but as previous research in the Andaman Sea disclosed, large-amplitude internal waves (LAIW) impact the coral populations located on the exposed western side of islands establishing a higher degree of environmental variability which raised the upper thermal tolerance of the corals located at these exposed sites in comparison to corals located on the eastern sheltered side. We tried to better understand the mechanism to thermal resilience by studying the ability to acclimate to two different environmental conditions and conducted a nine month reciprocal cross transplant with corals of the genus Porites lutea around the island Koh Racha Yai in the Andaman Sea which is impacted by LAIW and implemented a thermal stress experiment in succession. This thesis focused on the ability of the local environment to influence animal host traits and the capacity of the background environment to modulate its stress tolerance and in addition, the respective contribution of the host animal and the symbiont to local acclimation and stress tolerance. Coral transplants showed trends by approximating towards trait levels characteristic for corals native to the environment but because differences in monitored host traits between exposed and sheltered populations where not significantly different from each other in general, transplants could not show strong signs of acclimation. Because corals only expressed significant differences between exposed and sheltered sites in a number of symbiont traits, acclimation could be observed in the approximation of the symbiont parameters: zooxanthellae count, chlorophylla content and with that the color score which all shifted to a significant degree away from their origin location matching levels of the population native to the novel location. The environmental forcing of the sheltered location was not as impactful on the stress response of the transplant groups and seemed to be more affected by the exposed environment. Since host parameters did not show pronounced differences between population groups but survival rates did, this study suggest that stress resilience in the examined coral populations are best explained through the symbiont parameters.