Effects of Different Water Turbidity Levels on the Survival, Growth and Physiology of the Eelgrass Zostera marina

An increase in water turbidity is one of the main factors underlying seagrass meadow degradation. The effect of different water turbidity levels [2 (control), 10, 20, 30, and 40 NTU] on the survival, growth and physiology of eelgrass (Zostera marina) was studied through a 3-month indoor experiment. The results showed that the survival rate of eelgrass decreased gradually with an increase of water turbidity, and the survival rate under 10–40 NTU conditions was significantly lower than that of the control group (P < 0.05). In particular, the survival rate of eelgrass exposed to 40 NTU was only 56.1% that of the control group. With an increase of water turbidity, the growth rate and productivity of eelgrass also showed a decreasing trend. In the 40 NTU treatment group, the internode elongation rate and leaf elongation rate of eelgrass reached minimum values, which decreased to 48.9% and 61.6% of that of the control group, respectively. Compared to the productivity of the control group, aboveground and underground productivity decreased by 64.6% and 78.8%, respectively. Correlation analysis showed that the increase of water turbidity mainly affected the growth and survival of eelgrass by affecting the content of nonstructural carbohydrates. The content of nonstructural carbohydrates in eelgrass decreased gradually with an increase of water turbidity, and the content of carbohydrates in plants exposed to 10~40 NTU was significantly lower than that in the control group (P < 0.05). The aboveground soluble sugar content in eelgrass exposed to 10–40 NTU was 20.2%–74.7% lower than that in the control group. The results showed that a long-term increase of water turbidity led to a significant decrease in the nonstructural carbohydrates of eelgrass, which was not conducive to its growth and survival. The results provide a theoretical basis for clarifying the degradation mechanism of Z. marina seagrass meadows and selecting suitable restoration areas.