Abstract

Seagrass meadows fulfil many essential ecological functions of which an important one is to stabilize sediment. Therefore, they are perceived as a nature-based alternative or addition to conventional rigid coastal protection. The magnitude of the impact by seagrass meadows depends on their morphology such as canopy height, stem density and spatial extent. However, deciduous, intertidal seagrass species are often simplified in modelling 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 change of seagrass properties for morphological development of a tidal basin in the Wadden Sea as an exemplary study. We applied numerical modeling to simulate the annual growth cycle of seagrass meadows and their interaction with hydro-morphodynamics. Based on validated seasonal change of seagrass properties by field surveys and comparison 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 the seagrass meadows and even predict contrary results to simulations considering seasonal change of seagrass properties for the net sediment volume change in the intertidal zone. This points out the essential necessity of considering natural growth and decline cycles of seagrass meadows when assessing their role in coastal protection, especially in temperate zones where seasonal change of seagrass properties is distinct.