The Importance of Seasonality in Seagrass Properties for Coastal Hydro‐Morphodynamics—A Case Study in a Wadden Sea Basin

Seagrass meadows fulfill many essential ecological functions, of which an important one is to stabilize sediment. Therefore, they are perceived as a nature‐based addition or alternative to conventional rigid coastal protection. The impact of seagrass meadows depends on their morphology, such as canopy height, shoot density, and spatial extent. However, deciduous, intertidal seagrass species are often simplified in modeling studies by adopting their annual mean height and density. This can lead to an erroneous estimate of their impact on hydro‐morphodynamics and misconceptions about their contribution to coastal protection. Here, we assess the importance of seasonal changes in seagrass properties for morphological development, using a tidal basin in the Wadden Sea as an example. We applied numerical modeling to simulate the annual growth cycle of seagrass meadows and their interaction with hydro‐morphodynamics. Based on validated seasonal changes in seagrass properties from field surveys and comparisons between scenarios of seagrass growth, our results show that adopting static seagrass parameters in modeling can lead to over‐ or underestimation of morphological changes induced by seagrass meadows. In some cases, it may even predict results contrary to simulations that consider seasonal changes in seagrass properties, particularly regarding the net sediment volume change in the intertidal zone. This highlights the essential necessity of considering the natural growth and decline cycles of seagrass meadows when assessing their role in coastal protection, especially in temperate zones where seasonal changes in seagrass properties are distinct.