Elucidating the impact of light on the physiological performance of Pocillopora acuta in an in situ experiment across varied local environments

Corals are highly sensitive to environmental change, with light and temperature acting as major stressors that disrupt their narrow physiological tolerance. While elevated temperature is a well-established driver of coral bleaching, increasing evidence highlights high irradiance as a critical factor exacerbating stress responses. To elucidate the impacts of environmental factors such as temperature and light on coral physiology and enzyme activity, we conducted an in situ study on Pocillopora acuta from two distinct reef sites in Phuket Province, Thailand, located in the Andaman Sea: Maiton Island (MT), a clear-water reef with higher light level, and Panwa Cape (PW), a turbid reef with lower light levels. Four treatments were involved in the investigation, and the following coral transplants were made: (1) from Maiton Island (NMT) native corals kept at their original reef; (2) corals crossed from Panwa Cape (CMT) to Maiton nursery; (3) from Panwa Cape (NPW) native corals kept at their original reef; and (4) corals crossed from Maiton Island (CPW) to Panwa nursery. Our results show that high light exposure (NMT and CMT) strongly suppressed photochemical efficiency, altered pigment composition, produced excess ROS, which evidenced the photodamage and impaired recovery potential, a history of high-light exposure did not confer resilience, as NMT corals exhibited similar stress signatures to transplanted corals (CMT). In contrast, corals in the turbid PW environment (NPW and CPW) maintained more stable photophysiological and biochemical profiles, suggesting that reduced light and higher particulate availability buffered declines in symbiont density and mitigated oxidative pressure. These findings highlight that turbidity may provide a functional refuge by reducing light induced stress. Understanding how corals respond to such local environmental gradients is essential for improving the modeling of bleaching risk and identifying habitats with potential resilience under future ocean change.