Mangroves protect the coastline from erosion
Shrimp in traditional shrimp ponds, gei wais, use mangrove forests as shelter and nursery grounds.
Shrimp and some species of fish larvae from the sea are flushed into these ponds where there are plenty of nutrients, derived from the decomposition of leaves. Mangrove forests are one of the primary natural features of coastlines throughout the tropical and sub-tropical regions of the world. They grow in the muddy and swampy areas which are sometimes called 'wetlands', and are among the most productive ecoystems.
Scientists estimate that one hectare of mangrove can support as much as 450 kilograms of prawn per year and 700 kilograms of offshore fish.
Besides, each hectare of mangrove forest can support 120 tonnes of biomass per year, including insects, reptiles, amphibians, birds, invertebrates and many water micro-organisms.
There are five basic elements that play an important role in the extensive development of mangroves.
Tropical temperature, normally between 18 and 28 degrees Celsius Fine-grained alluvium Shores free of strong waves and tidal action Salt water Large tidal range Mangroves are essentially tropical in distribution. The largest area of mangrove in Hong Kong is at Mai Po, an area of more than 100 hectares, which is greater than the total area of 100 standard fields.
Together with the mangroves around Deep Bay, this area is the sixth largest mangrove forest in south China. Also, there are many smaller patches around the New Territories such as Sai Kung and Tai Po and along the north coast of Lantau Island. Mangroves supply nutrients and oxygen which are important for plants and animals to survive in the mangrove ecosystem.
Moreover, mangroves help to stabilise shorelines in coastal streams and estuaries (especially during storms and typhoons by protecting them against tidal waves which would otherwise erode the shoreline). Since most mangrove species can absorb inorganic substances through their roots, they serve as natural water treatment plants.
