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.