As the bottom gets shallower, the mangroves can grow further out, while those on the inside eventually find themselves on dry land, where they are replaced by land plants. In this way the mangrove forest advances slowly outward, leaving land behind. Even in areas where there is not enough sediment to build new land, the mangroves protect the shoreline from being washed away in storms. The roots and trunks break the force of the waves, and the leaves and branches reduce the effects of the wind and rain. There are examples of islands which were built by mangroves, and then washed away when the mangroves were cut.
Mangroves are an important source of food and materials for many coastal people.
Crabs, clams, oysters, fish and other food are often collected there. Even the mangrove fruits are sometimes eaten. Mangrove wood is often collected as firewood, and it can also be used for building. The bark has tannin which has craft and medicinal uses. Even in the city, mangroves can be important.