The Combined Effect of Seawater Salinity and Duration on the Survival and Growth of Eelgrass Zostera Marina

Abrupt changes in salinity are considered a key cause of seagrass bed degradation. In the study, we first quantified the effects of different combinations of salinity and duration on the responses of Zostera marina shoots in terms of survivorship, morphology, growth and physiology. The recovery potential of Z. marina shoots was assessed. The LT50 (lethal time that caused an increase in mortality to 50% of that of the control) and EC50 (effect concentration, i.e., salinity level that caused a decrease in growth to 50% of that of the control) were calculated to reveal the quantitative relationship between salinity and duration that resulted in limiting effects on the survival and growth of Z. marina shoots. Z. marina shoots were exposed to different combinations of water salinity [25, 30 (control), 35, 40, and 45 PSU] and duration (5, 10, 15 and 20 days), and then the shoots were transferred to the control condition for over 30 days under laboratory conditions. The results showed that the survival rate of shoots at the end of recovery were significantly lower than those of shoots at the end of direct salinity stress at the salinity levels of 40 and 45 PSU in each duration, indicating that short-term periods of obviously increased water salinity would lead to long-term effects on the survival of Z. marina shoots. Regression analysis revealed that the relationship between salinity and duration was a strong power function that could limit the growth of Z. marina. Pearson correlation analysis showed that the survival and growth of Z. marina shoots exposed to different salinity levels were significantly correlated with leaf soluble sugar contents when the duration was higher than 5 days. This study will further enhance our understanding of seagrass bed degeneration induced by abrupt changes in salinity.