Responses of eelgrass seed germination and seedling establishment to water depth, sediment type, and burial depth: implications for restoration

When seagrass beds are restored by seeding, many factors affect the transition of seeds to seedlings. In this study, the effects of water depth (light availability), sediment type, and burial depth on seed germination and seedling establishment of Zostera marina L. were tested through 2 in situ suspended culture experiments in Ailian Bay, China. In the first experiment, water depth (1, 3, and 6 m) had no significant effect on seed germination and seedling establishment, but did affect seedling survival. In the second experiment, seed burial depth (2, 5, and 10 cm) had significant effects on seed germination and seedling establishment. Seeds buried at shallow depths exhibited higher percentages of seed germination and seedling establishment, and maximum values (mean ±SD = 21.33 ± 9.30%) were recorded in seeds buried at 2 cm in 100% sand. There was no significant effect of sediment type on seed germination and seedling establishment at 2 cm (p > 0.05), but seeds buried at 5 cm were affected by sediment type, with seeds cultured in 100% sand exhibiting the highest percentages of seed germination (12.33 ± 4.51%) and seedling establishment (12.33 ± 4.51%). No seedlings or germinated seeds were found at 10 cm, regardless of sediment type. Once plants are established, sediment type and seed burial depth do not play a decisive role in plant growth, with plants performing equally in terms of shoot density (33-90 shoots per pot) and shoot height (20 ± 6 cm) in different sediment types and at different burial depths 1 yr after seedling establishment. Our findings help clarify the complex combined effects of sediment type and burial depth on seed germination and seedling establishment.