Seed dispersal of East Asian coastal dune plants via seawater – short and long distance dispersal

Coastal plants provide precious and irreplaceable services to human and coastal ecosystems, but people are still rather unaware how coastal plants relate with sea tides. We assumed that their seeds may reflect some relationships with tides. Our objective was to understand seed dispersal of plants living in the upper coastal regions, not reached by normal tides, but inundated by storm surges. For this purpose, we observed seed characteristics, especially seed buoyancy, of coastal and non-inundated plants of the Shandong Peninsula, north China. Through field simulation, we studied how buoyancy affected the dispersal during tides, using twig segments as retrievable dummies of seeds, in order to collect evidences with concern, how seed dispersal could occur during storm surges, which are extremes of tides. Coastal plants had predominantly buoyant seeds, while inland-growing plants had largely non-buoyant seeds. Ninety percent of buoyant twig segments (mimicking seeds) were recaptured after tides on experimentally used coastal areas; only 1% of non-buoyant ones of such dummies were recaptured, whereas the rest probably had been swept away by wave action to deposit at the sea bottom. Buoyant twig segments (mimicking seeds) dispersed along the coastlines as tides surged towards the coast. About 10% of these buoyant twigs were swept away with off-shore currents, but they might land elsewhere, similar as it might happen with long-distance dispersal of seeds.