“If there are no Mangrove Forests, then the sea will have no meaning. It is like having a tree with no roots, for the mangroves are the roots of the sea.”
—fisherman, Trang Province, southern Thiland
Mangrove forests, together with their adjacent intertidal environments are among the most productive ecosystems on the earth. The great importance of these ecosystems to marine fauna was shown by Odum and Heald14 and has led to an interest in their conservation. Continuing loss of mangrove systems has, among other causes, been attributed to erosion of delicate coastal wetlands.
In a broad floristic sense, mangroves include about 53 species in 23 genera and 16 families. However, Tomlinson15 recognises 34 species in nine genera and five families as exhibiting restriction to mangrove environments in which they play a major role and having specialised adaptations to this unique environment.
Fig: 1.1: Mangrove distribution in India
The name ‘mangrove’ is applied to other unrelated constituents of mangrove vegetation, such as Avicennia nitida, a bush of the vervain family, called black mangrove. True mangroves are classified in the division Magnoliophyta, class Magnoliopsida, order Rhizophorales, family Rhizophoraceae.
Mangrove, a large tropical evergreen tree, grows on muddy tidal flats and along protected ocean shorelines. Mangrove ecosystems are found throughout the tropical regions of the world. They are most abundant in tropical Asia, Africa, and the islands of the SW Pacific.
Several mangroves produce from their trunks aerial roots that become embedded in the mud and form a tangled network; this serves both as a prop for the tree and as a means of aerating the root system. Such roots also form a base for the deposit of silt and other material carried by the tides, and thus land is built up which is gradually invaded by other vegetation. Some mangrove species lack prop roots but have special pores on their branching root system for obtaining air. The mangrove fruit is a conical reddish-brown berry. Its single seed germinates inside the fruit while it is still on the tree, forming a large, pointed primary root that quickly anchors the seedling in the mud when the fruit is dropped.
Mangroves have been harvested destructively on a large scale; the bark is a rich source of tannins, and the wood is used for wharf pilings and other purposes.
Fig: 1.2: Aerial roots Fig: 1.3: Prop roots
Mangroves provide a vide range of services and benefits to the mankind. Ecological and economical values of mangroves are recognized world over. They are instrumental in providing ecological and livelihood security to coastal regions and people. People are making use of mangroves by protecting them as a nursery ground for various fish and crab species, which form a part of their daily food. Good use of mangrove areas can be made for eco-tourism and tourists from India and abroad for a pleasant trip and crocodile watching.
Mangroves have long functioned as a storehouse of materials providing food, medicines, shelter and tools. Fish, crabs, shellfish, prawns and edible snakes and worms are found there. The fruit of certain species including the nypa palm can be eaten after preparation along with the nectar of some of the flowers. The best honey is considered to be that produced from mangroves, particularly the river mangrove Aegiceras corniculatum. Numerous medicines are derived from mangroves. Ashes or bark infusions of certain species can be applied to skin disorders and sores including leprosy. Headaches, rheumatism, snakebites, boils, ulcers, diarrhoea, hemorrhages … and many more conditions are traditionally treated with mangrove plants. The latex from the leaf of the blind-your-eye mangrove Excoecaria agallocha – claimed to cause blindness13 – but the powerful chemicals in it can be used on sores and to treat marine stings. The leaves are also used for fishing; when crushed and dropped in water, fish are stupefied and float to the surface. This sap is currently being tested for its medical properties and may play a part in western medicine. Certain tree species, notably the cedar mangrove, cannonball mangrove (relatives of the red cedar) and the grey mangrove, are prized for their hard wood and used for boat building and cabinet timber as well as for tools such as digging sticks, spears and boomerangs. The fronds of the nypa palm are used for thatching and basket weaving. Various barks are used for tanning, pneumatophores (peg roots) make good fishing floats while the wood from yellow mangroves (Ceriops species) has a reputation for burning even when wet.
Fig: 1.4: Pneumatophores or peg roots of mangrove plants
Ethnobotany and medicinal uses: Many of the substances in the wood and bark, the Diaspora and the leaves of different types of mangroves for instance the Indian Mangrove (Avicennia officinalis), the Black Mangrove (Avicennia germinans) are used in traditional medicine they are however also used as poisons. The Black Mangrove is used for diarrhoea and rheumatic aliments. The resin of black mangroves is among other things used as medicine against tumours, insect repellents can also be made out of its resin. In Uthoff (1996) one can find an outline of the manifold and long-range ethno-pharmaceutical usages. Up until today most of the substances have not been examined for their effectiveness. In the genetic pool of our mangrove ecosystem there is presumably a large potential for the discovery of powerful substances for modern medicine.
The mangrove extracts were a source of mosquito larvicidal compounds, as well as of polyphenols highly active against viruses such as HIV and Hepatitis B virus16 .
Ecology and Mangroves
1. Prevention from soil erosion and stabilization of coasts and beaches
2. Protection of land from tidal surges and cyclonic storms.
3. Provides an excellent home to different plant species, birds and animal
4.Useful as eco-tourism niche for educational and recreational purpose
Local population put the mangroves to several uses including the following:
1.Provides fuel wood, green manure, charcoal, timber, etc
2.Used for boat / canoe making
3.Used for thatching material, cordage and rope material
4.Used for medicinal purposes.
5.Useful for to produce honey and bye products..
Threats to mangroves: The threats are as given below, Man and his greed being the greatest threat:
(1) Conversion of mangrove areas : It has been observed that mangroves in private areas / khazan lands face threat due to conversion of these lands for human habitation, aquaculture, agriculture and other developmental activities. Reclamation of these areas results in damage to saplings and small mangrove plants in general. Sporadic incidents of felling of trees illegally for conversion of land have also been reported, though damage due to this is almost negligible, as per official records.
(2) Unauthorized felling: Cutting of Trees and branches of mangroves for firewood purpose, house and fence construction, reclamation of land etc is common.
(3) Pollution : Oil slicks, solid waste disposal, industrial effluents etc. pollute the mangrove habitat and thereby affect them adversely.
(4) Fishing : Illegal fish / fishling culture / aquaculture is common in Mangrove forests. Fishing using dragnets is common. This results in damage to the young regeneration and plantations. Besides, fisherman find mangrove regeneration an obstacle in their fishing activity and they uproot / damage the young crop and this is one of the major threats to the mangroves.
(5) Insect attack / diseases: There are some species of insects or borers, which cause considerable damage to the stems and therefore to the mangroves. Besides, insect attack on the leaves of Rhizophora mucronata has been observed to take place regularly, which some times results in total damage to young plants. Also, insect attack on Avicennia alba is observed at a regular interval of 5 years, where the larvae of the insect eat all the leaves of the plants and make them leafless and causes severe damage to young crop. Fungal attack on the leaves of plants has also been observed, mainly on the leaves of Sonneritia alba, and other species also found to have been attacked by fungus.
(6) Barnacle infestation: Plantations and young plants are being damaged by the attachment of barnacles to their stem. The plant affected generally is Rhizophora mucronata, which probably is due to its rough bark, thereby providing a good substratum for their attachment