Saltmarsh seeds in motion: the relative importance of dispersal units and abiotic conditions

Propagule dispersal is fundamental to the colonization of new habitats, metapopulation connectivity, and gene flow and thus enables saltmarsh species to cope with global change. In this study, mesocosm and flume experiments were used to quantify the effects of different dispersal units (i.e. seed, spikelet, inflorescence, and plant fragment-containing seeds) and abiotic conditions on the dispersal processes of 4 globally distributed saltmarsh species: Salicornia europaea, Scirpus maritimus, Spartina anglica, and Elymus athericus. The results showed that (1) moving seawater has a species-specific effect on buoyancy, leading to prolonged floatability of high tidal-flat species E. athericus and reduced floatability of pioneer species; (2) tidal currents increase dispersal speed, whereas wind can have additive or antagonistic effects on currentdominated dispersal speed depending on its direction; (3) wave action reduces dispersal speed, but this effect becomes smaller with increasing wave magnitudes and/or applied co-directional wind; (4) dispersal speed may vary depending on the physical forcing and type and morphology of the dispersal units, but the largest species effect is related to the period in which units remain buoyant; and (5) the dispersal potential of saltmarsh species in wind wave-dominated coastal environments can be ordered as follows: E. athericus > S. maritimus > S. anglica > S. europaea. This study provides valuable guidance for future numerical hydrodynamic models of salt - marsh dispersal and establishment, allowing more accurate prediction of the distributional responses of saltmarsh species to climate change, thereby supporting appropriate management and restoration strategies.