A review of 14 studies conducted worldwide shows that salt marshes slow waves and stabilize shorelines. Wider marshes with more dense vegetation and higher biomass slow waves to a greater extent and stabilize shorelines more effectively.
Shepard, Christine C., Caitlin M. Crain, and Michael W. Beck. (2011). The protective role of coastal marshes: a systematic review and meta-analysis. PLoS One, 6(11), e27374.