Planting seagrass like this protects the beach from erosion of storms. Communities up and down the coast of Florida are always looking for ways to preserve the beaches. In some places they dredge up the sand from just beyond the shoreline and place it back on the beach. That'll last for a couple years depending on the storms and then it needs to be done again. Plants are a natural approach, only they are usually used to protect only the entrance to the beach which usually involves some type of dunes like these.
From daily images