Development of Seed- and Shoot-Based Restoration Approaches for the Eelgrass Zostera marina: The Combined Effect of Sediment Loosening and Fertilization

We subjected seeds and shoots of eelgrass Zostera marina to different combinations of sediment loosening (0 (control), 5, 10 cm in depth) and sediment fertilization (0 (control), 40, 80, 120, 160 g/m²) through a field experiment involving seed sowing and shoot transplantation from September 2020 to September 2021. Growth analysis revealed optimum ranges for sediment fertilization and sediment loosening were 88.8–93.8 g/m² and 5.3–5.8 cm for Z. marina seed sowing, as well as 79.7–86.7 g/m² and 5.9–6.5 cm for Z. marina shoot transplanting, respectively. The shoot densities of Z. marina exposed to these optimum range of sediment fertilization and sediment loosening were 1.1–1.3 times of those in the control group. Porewater nutrients are key environmental factors affecting seed germination and shoot growth of Z. marina. The results provide valuable insights for enhancing restoration effects of Z. marina.