The success of seagrass restoration using Enhalus acoroides seeds is correlated with substrate and hydrodynamic conditions

Abstract

The extent of seagrass areas and their associated ecosystem functions and services have been declining due to many factors. Seagrass restoration is important to mitigate such declines. Seagrass restoration using seeds can be a viable method due to the high seed availability of some seagrass species and could enhance seagrass resilience to climate change stress. However, this method sometimes has low success rates due to high seed predation and seeds being washed away by wave action or substrate movement. The research was conducted to compare the settlement of Enhalus acoroides seeds and the establishment of seedlings on different sediment types (fine sand, coarse sand, and hard substrate with rubble) combined with different wave exposure levels (high and moderate). This is the first study to observe seed survival and seedling establishment of the tropical seagrass E. acoroides in the wild. On average, 64% of seeds dispersed on fine sand substrate at a moderate exposure site survived and developed into established seedlings by the end of the 40 days observation period, but the survival of seeds dispersed on coarse sand at high exposure and hard substrate at moderate exposure only remained above 50% for up to 3 days, and had declined to 2% and 1.4%, respectively, by day 40. Six years later, surviving E. acoroides sample from the coarse sand and hard substrate both had well-developed rhizomes but fewer roots than the plant from the fine sand site, these rhizome and roots characteristics were likely adaptations to increase anchoring capacity in the specific site. The results indicate that Enhalus seed settlement and seedling establishment can readily occur at sites with fine sand substrate and lower wave exposure; however, additional measures may be required at more exposed sites with mobile or hard substrates until seedlings become established.