The importance of Seasonality for Seagrass as Coastal Protection

Seagrass is regarded with great expectations when it comes to nature-based coastal protection measures. Seagrass meadows dampen waves, reduce currents, and stabilize sediments in the coastal environment. However, most modeling studies estimating the magnitude of the coastal protection effect by seagrass assume a constant seagrass cover throughout the year. In temperate climates such as Northern and Central Europe the seagrass cover has considerable annual and interannual variations. The seagrass cover is highest in late summer and autumn and lowest in winter and early spring. At the same time, the physical forcing of waves and currents is at its maximum in winter, indicating a discrepancy between the seasons with the highest benefits of seagrass to coastal protection and the seasons with the most threat to the stability of the coast. In this study, we use a 3D baroclinic circulation model (SCHISM) coupled with a sediment model and a model of seagrass growth dynamics for estimating the significance of seasonality for coastal protection. A case study of a tidal basin in the northern Wadden Sea indicates that disregarding the seasonality can lead to substantial overestimations of the effectivity of seagrass for coastal protection.