Mangroves are a group of about 80 different salt-tolerant species of trees. They can live along the intertidal zones of tropical and sub-tropical coastlines. Their roots stand the ebb and flow of tides. The roots slow the flow of the tidal waters. This lets sediment settle and build up as nutrient-rich mud. The habitat is a valuable shelter and breeding site for fish. It stabilises coastlines, and reduces erosion from storm surges and tsunamis.