Mangroves and estuaries

Abstract

Mangroves are forests of salt-tolerant trees and shrubs that grow in the shallow tidal waters of estuaries and coastal areas in tropical regions. They require slow currents, no frost and plenty of fine sediment in which to set their roots. Their muddy waters, rich in nutrients from decaying leaves and wood, are home to sponges, worms, crustaceans, molluscs and algae, and provide shelter for marine mammals, snakes and crocodiles. They act as fish nurseries and help feed life further out to sea. QueenslandÕs mangroves, for instance, do much to sustain the Great Barrier Reef, the worldÕs largest coral reef system. Mangroves are also strongly correlated with the presence of shoals of shrimp further offshore. Mangroves extend over 18 million hectares worldwide, covering a quarter of the worldÕs tropical coastline1. They dominate the river deltas and tidal creeks of Southeast Asia from Thailand, Burma and Vietnam through Malaysia to Indonesia, with more than 5 million hectares around the thinly populated islands of New Guinea and Borneo alone2. The largest single system is the 570 000 hectares of the Sundarbans of Bangladesh, which harbor the Bengal tiger and sustain some 300 000 people.