Population specific salinity tolerance in eelgrass (Zostera marina)

Salinity is one of the main factors impacting distribution of marine plants and sub-optimal salinities may result in increased resource use and decreased production. We studied the performance and salinity tolerance of eelgrass (Zostera marina L.) originating from two regions with different ambient salinities: a low saline (salinity 6) and a high saline (salinity 20) population. Plants from both populations were exposed to a series of fixed salinities (2, 4, 6, 9, 12.5, 15, 20 and 25) for 5 weeks. Both plant origin and salinity affected plant performance significantly. Plant production decreased with decreasing salinity in both populations, while mortality increased in low salinity only in plants originating from the high saline population. The better performance of the low saline population in the lowest salinities indicates a horizontal shift in salinity tolerance among populations with different origin and that the low saline population is better adapted to hyposaline conditions. Despite the long-term adaptation of the low saline population to stable, low salinity, these plants were still able to function normally in high salinities, indicating remarkable plasticity. The results further suggest that altered salinity can severely impact seagrass productivity but responses might vary significantly depending on plant origin. Such variability in stress tolerance indicates that some populations have better chances to survive in and adapt to future changes in environment.