Assessing Anthropogenic Salinity Stress from Desalination Brine on Seagrass Using Biochemical Indicators in the Gulf of Aqaba

The expansion of seawater desalination in arid and semi-arid coastal regions produces hypersaline brine discharges that constitute an increasing anthropogenic pressure on marine ecosystems. Although large-scale ecological impacts are often difficult to detect, sub-lethal physiological stress in habitat-forming species may provide early indications of environmental disturbance. Seagrasses are particularly relevant in this context due to their ecological importance, sediment-stabilizing role, and sensitivity to changes in water chemistry. This study investigates the physiological responses of the tropical seagrass Halophila stipulacea to simulated desalination brine exposure using controlled laboratory experiments and biochemical stress indicators.
Intact H. stipulacea plants together with their associated sediments were collected from a protected coastal site adjacent to the Marine Science Station in the Gulf of Aqaba. The Gulf of Aqaba is a semi-enclosed, oligotrophic basin characterized by limited water exchange and increasing coastal development, making it particularly sensitive to localized anthropogenic pressures such as desalination activities. After laboratory acclimation, seagrass–sediment units were maintained under controlled conditions and exposed for two months to elevated salinity treatments of +1%, +5%, and +10% above ambient seawater salinity. These treatments were selected to simulate realistic salinity gradients that may occur in the vicinity of desalination brine discharge zones.

Physiological stress responses were assessed using a suite of biochemical indicators, including antioxidant defense enzymes (catalase, superoxide dismutase, and glutathione-S-transferase) and lipid peroxidation (LPO) as a marker of oxidative membrane damage. The results revealed clear salinity-dependent responses, with progressive activation of antioxidant defenses as salinity increased. At higher salinity treatments, significant elevations in LPO were observed, indicating oxidative damage at the cellular level. Overall, H. stipulacea exhibited measurable physiological stress from +5% salinity onward, while exposure to +10% salinity resulted in pronounced oxidative damage, suggesting a transition from adaptive physiological adjustment to cellular impairment under prolonged hypersaline conditions.

The findings demonstrate that moderate but sustained salinity elevations associated with desalination brine can induce sub-lethal physiological stress in seagrass ecosystems prior to visible structural or ecological degradation. By incorporating intact plants and their sediments, the experimental design better reflects natural plant–sediment interactions and enhances ecological relevance. The applied biomarker-based approach provides a cost-effective and sensitive early-warning framework that can complement conventional monitoring methods. This approach is well suited for integration into environmental impact assessment and long-term monitoring programs aimed at managing anthropogenic pressures on marine ecosystems in the Gulf of Aqaba and comparable coastal systems worldwide.