Mangrove includes mangrove dominated forests, litter laden forest floors, mudflats, adjacent coral reefs and contiguous water course like rivers, bays, intertidal creeks and channels and backwaters.
Mangroves exchange matter and energy with adjacent marine, freshwater, and terrestrial ecosystems (CAMP Workshops, 1987) Indian mangroves can be broadly divided into east coast deltaic and west coast non-deltaic mangroves. In addition, there are mangroves in Andaman and Nicobar Islands.
Mangroves cover an area of 190,000 to 240,000 km2, occupying about one-quarter of world’s coastal line. Largest mangrove areas occur in Indonesia (30%), followed by Nigeria (10%), Australia (8%) and Mexico (7%).
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India contributes approximately 3% to world mangrove area. Largest stretch of mangroves lies in Sunderbans in West Bengal covering an area of about 4,200 sq. km. earliest mangrove species appear to be originated in Indo-Malayan region. Mangroves contribute to food chain that supports coastal fisheries.
These ecosystems are quite productive (350-500 g C m2 yr-1)5 and may show a strong, weak or no special zonation (Tomlinson, 1986) although abundance of individual species may follow salinity gradient. Most species are quite plastic to salinity and prefer a salinity range of 5-30 parts per thousand.
Ecological investigation on Indian mangrove is poor. One hundred and sixteen plant species are recorded including 59 mangrove 47 algae- and 10 sea grass species. About 65 vascular plant species belonging to 31 families and 59 genera are reported. East coast has 64 vascular species from 42 genera and 29 families.
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West coast has 33 species from 24 genera and 19 families. Andaman and Nicobar Islands represent 43 species from 30 genera and 23 families (Banerjee et al., 1998). Eight species occurring on east coast are not represented in west coast. Sunderban alone has 62 species (Banerjee and Ghosh, 1998).
Predominant mangrove species are Avicennia officinalis, Excoecaria agallocha. Heritiera fames, Brugiera parviflora, Ceriops decandra, Rhizophora mucronata and Xylocarpus granatum. Other major genera are Acanthus, Acrostichum, Aegialitis, Aegiceras, Brownlowia, Caesalpinia, Cerbora, Clerodendron, Cynometra, Dalbergia, Derris, Dolichandrone, Finlaysonia, Hibiscus, Hoya, Intsia, Ipomoea, Kandelia, Lumnitzera, Merope, Mucuna, Myriostachya, Nypa, Phoenix, Salvadora, Sarcolobus, Scyphiphora, and Tylophora.
Macro-level environmental factors that determine area, species diversity and biomass of mangrove wetlands of India have analyzed and major mangrove wetlands are classified as tide-dominated, river-dominated and drowned-river valley type (Selvam, 2003).
Bunding, erosion and deposition cause changes in tides and currents, which in turns have impact on mangroves. Herbicides and defoliants applied in coastal crop lands pollute mangrove habitats.
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Mangroves metabolize organic wastes and are termed as natural sewage treatment works. They utilize excess nutrients to increase productivity although continuous excessive inputs of nutrients may adversely affect mangroves. Mangrove vegetation of Kaveiy delta has substantially suffered due to geomorphic and anthropogenic interferences. Structural changes are noticed in Pichavaram and Muthupet areas.
Out of 6986 and 6559 ha of mangrove area respectively in Bhitarkanika and Mahanadi sites in Orissa, 5-30% and 20-60% degraded mangrove vegetation are recorded. About 20 villages in Mahandi area and 59 villages in Bhitarkanika area depend on mangroves from Chilka. Hetamundia, Kujary and from Istharus of Subernarekha and Jatadhar have already disappeared.
Forests of Bagapatia and Sunei-Rupei were cleared for rehabilitation purposes. Conflicts between traditional and commercial fishing practices degrades mangrove. Mangrove areas are ideal to undertake conventional aquaculture practices which do not damage ecosystem.
Small scale community based fisheries may be encouraged as 95% of coastal population is engaged in this sector. Such communities use only 10% of energy of large scale fisheries corporate sector to contribute half of world catch.
Interest and right of local communities must be safeguarded. Prawn farming projects, which are established close to mangrove and estuarine areas, for earning large sums of money in shortest possible time, need to be discouraged for their adverse affects on ecosystems. Mangrove areas can be used for development of ecotourism, recreation, education and for creating public awareness on aspects of nature conservation (IUCN, UNEP, WWF, 1991).