Mangroves on Carey Island. Coastal vegetation, in particular mangrove trees, are an important natural protection against waves, helping to prevent soil erosion by effectively slowing the speed of sea water reaching the coastline. They are the second line of defense after coral reefs, and are home to a range of fish, crab, shrimp, and mollusc species, providing an important source of food and economic revenue for coastal communities. The tsunami of 2004 left a horrific human tragedy in its wake but also some lessons. Among them was the tremendous importance of mangroves, which, according to some experts, are one of the world's most threatened tropical ecosystems.