Mangrove propagule survival and growth on dredged sediments strongly depends on sediment type and secondarily on tidal inundation regime

Mangrove restoration requires in-depth understanding of the environmental conditions that support successful establishment and growth of planted propagules. The re-use of dredged sediments offers the potential to create suitable intertidal sediment beds for mangrove habitats. Yet there is limited empirical evidence on their effectiveness to support mangrove propagule survival and seedling growth. We conducted a field experiment to assess the early survival and growth of Rhizophora mangle L. propagules across dredged sediment types varying from non-cohesive sand to cohesive mud; and different tidal inundation levels. We monitored abiotic drivers including tidal inundation duration, frequency, and depth; and erosion and sedimentation rates. Propagule performance was quantified through survival, shoot emergence rate, plant height and number of leaves. Most propagules were lost in the low-cohesive sandy sediments where erosion was largest, whereas survival was highest in high-cohesive muddy sediments with significantly less erosion. Propagule growth performance (e.g., larger number of leaves, plant height and shoot emergence rates) was consistently enhanced at the low inundation levels (i.e., inundation <40% of the total experimental period). These findings demonstrate that cohesive dredged sediments can be re-used to create intertidal sediment beds that support mangrove establishment, while reduced inundation promotes propagule growth. This is most effective when cohesive, well drained muddy sediments are placed at higher elevations within the tidal frame, where inundation level and propagule loss risk is reduced. In contrast, non-cohesive sand increases erosion risk and propagule loss. These results provide practical guidance for optimizing mangrove restoration projects re-using dredged sediments.