The western coasts of coral islands facing the open Andaman Sea are exposed to large amplitude internal waves (LAIW) during winter to spring (January to April). LAIW entrain cold subpycnocline water into shallow reef areas causing frequent (several events per day) and severe drops in temperature (up to 9 ◦C) and pH (up to 0.6 units) and an increase in nutrients. It would therefore stand to reason that these waves have a direct impact on the formation of a coral reef framework, because it is widely believed that calcifying macroalgae in their role as important reef stabilizers and sediment producers need stable water conditions over a large temporal scale. The present study explored a possible impact of LAIW on the distribution, calcification, photosynthesis and respiration of the calcifying macroalgae Halimeda opuntia. The study was conducted at Racha island located about 18 km south of Phuket in the Andaman Sea. Belt transect observations along the island revealed that H. opuntia occured only at the eastern side of Racha. A combined transplantation and incubation experiment was performed. Algae were transplanted from the eastern to the western side of Racha island and after a two months adaptation period the algae were incubated at different pH and temperature treatments. Additionally, the temperature at the western and eastern side of Racha island was recorded for 6 months (October until March). The recorded data indicated no difference in LAIW intensity between the western and eastern coasts of Racha which is in contrast to other offshore islands in this region. The experiments showed that H. opuntia calcified faster and revealed higher photosynthetic rates after being transplanted to the western side in contrast to their eastern counterparts. The higher rates in oxygen production of the west-transplanted algae were maintained as well under simulated LAIW-conditions with reduced temperature and/or pH during the incubations. The calcification rates of east- and west-transplanted algae differed at reduced pH conditions but not when both pH and temperature were reduced. Despite the natural absence of H. opuntia along the western side of Racha island, this algae seemed to benefit from the natural conditions in the west in contrast to its common eastern environment. It may be concluded that factors other than LAIW such as less sedimentation and possibly higher light intensities in the west favored the development of the algae which may naturally be restricted to the east due to the lack of suitable settling substrate in west.