Salinity Tolerance of H. stipulacea - Will H. stipulacea Survive the Impacts of Desalination Plants in the Ocean?

One of the many potential effects of desalination plants on the nearby marine environments is the increase in salinity in the area of discharge. With almost half of the world’s desalinated water being produced in the countries of the Middle East, there is a rising concern of the effects of the these plants on marine ecosystems. Seagrasses form some of the most valuable ecosystems on earth, with an estimated value of $2.8 10⁶ sq km^-1 yr^-1. Salinity changes is one of the main factors impacting the distribution of seagrasses making it an important factor when studying effects of desalination in the marine environment. Halophila stipulacea, a native seagrass to the Red sea is often termed as a euryhaline (able to grow in wide ranges of salinity) species. One of the aims of this study was to find how tolerant H. stipulacea is to changes in salinities. Halophila stipulacea plants were collected from the northern Gulf of Aqaba, Red Sea (Eilat, Israel) and acclimated in mesocosms at similar conditions to the site of collection (40 PSU). Following acclimation, they were exposed to control (40], hypo (15, 20, 25) and hyper 55, 60 and 65 PSU) salinities for 3 weeks, followed by a 3-week recovery phase. Plants were followed over time for changes in growth parameters and photophysiology in parallel to changes in gene expression. Hyper and hypo-salinities caused a steady decrease in the growth of the plants, leaf area, photosynthetic ability (quantum efficiency of photosystem II- Fv/Fm) and in chlorophyll content. The plants seemed to recover from stress after returning to control salinity as indicated by the recovery in Fv/Fm, leaf count and chlorophyll content. Overall, plants coped less at 15 and 65 PSU. At 25, 55 and 60 PSU, plants could acclimate to the salinity with indications of stress. The results suggest that salinities as high as 60 PSU would not be a concern for the growth of H. stipulacea if that is the only effect of desalinitaiton plants.