The role of tides and winds in shaping seed dispersal in coastal wetlands

Global changes such as sea level rise and enhanced storminess motivate the use of saltmarshes as nature-based flood defenses. Yet, it remains poorly understood about how shifted environmental conditions may shape processes governing long-term stability of saltmarshes. Here, we integrated data from in situ measurements and field experiments in several Dutch salt marshes to probe the impacts of changes in tides and winds on seed arrival and seed retention on adjacent tidal flats, which is key to marsh regeneration following wave-driven lateral erosion. The results show that both the quantity and viability of the seeds transported toward adjacent tidal flats relate positively with the peak water level of each tide. Spring tides are more powerful in seed dispersal than neap tides, and storm-induced extreme water levels can serve as “Window of Opportunity” that deliver disproportionately higher amounts of viable seeds than average conditions. Seed retention decreased with growing onshore wind speed. Storm-induced strong wave disturbance can function as “Windows of Risk” that wipe out seeds on tidal flats at wind-exposed marshes. This study highlights the importance of variability in tides and winds for regulating the potential of seed-based marsh recovery on adjacent tidal flats and thus their resilience to lateral degradation. These findings are relevant for assessing the long-term marsh stability and sustainability of nature-based coastal defenses with saltmarshes under global environmental changes.