Abstract

--- - Desalination is increasingly used to produce potable water in arid coastal regions. However, this process generates hypersaline effluents (brines) that are discharged into marine environments, potentially affecting aquatic ecosystems. Since the ecological impact of brines depends on receiving environment characteristics, there is a growing need for sensitive biomonitoring tools. - The present study assessed the physiological and biochemical responses of Lessonia berteroana, a brown macroalgae endemic to the north-central coast of Chile, to salinity gradients and contaminants commonly associated with desalination processes. Laboratory exposure experiments evaluated stress responses using photosynthetic performance, pigment content, dehydration rate, total phenolic compounds, and lipid peroxidation as biomarkers. Tolerance thresholds were determined through 96-hour EC50 dose-response models. - The results identified salinity as the primary stressor for L. berteroana, with optimal physiological performance maintained at salinity increases of <= 15 % (similar to 38.4 practical salinity units (PSU) and a tolerance threshold approaching 51 PSU. The phosphonate-based antiscalant further reduced tolerance to 44.9 PSU, while combined exposure to brine, antiscalant, and coagulant lowered the threshold to 44.5 PSU. Among all biomarkers, lipid peroxidation exhibited the highest sensitivity, highlighting oxidative stress as a key physiological response mechanism. - These findings highlight the susceptibility of L. berteroana to brine discharges, particularly in the presence of chemical additives, and support its use as a sentinel species for detecting early-stage environmental impacts from desalination activities.