Abstract

Water desalination has become an important process to cope with water scarcity in the Mediterranean basin; however, the endemic seagrass Posidonia oceanica may be susceptible to high -salinity brines derived from this industry. To understand how brine affects metabolic processes in P. oceanica, transplantation experiments were performed in two sites exposed to a brine dilution plume derived from a desalination plant in Alicante (Spain). P. oceanica individuals were transplanted in three locations, i.e., a control site (-37 psu), an intermediate influence site (IB, -39.5 psu), and a high -influence site (HB, -42 psu), and were monitored for 6 days. The metabolic endpoints of reactive oxygen species (i.e., H2O2, lipid peroxidation, and ascorbate cycle) and the regulation of genes involved in antioxidant and osmoregulation responses [please complete sentence]. The concentration of H2O2 and thiobarbituric acid reactive substances (TBARS) increased, while that of ascorbate (ASC) decreased in HB, indicating excessive ROS production, lipid peroxidation, and antioxidant consumption. Genes related to osmoregulation (SOS1, SOS3, AKT2/3) and antioxidant response (GR, APX, FeSOD, MnSOD, and STRK1) were upregulated in brine -exposed plants, especially at the early stages of the experiment. This novel approach has provided a battery of biomarkers that may serve as early warning tools for rapid action mitigation to avoid the negative effects of salinity on P. oceanica at the population and community levels. This approach can be also globally applied to relevant macrophytes in environmental monitoring programs to address other stressors and their isolated or combined contribution to marine pollution.