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Abstract
Mangrove ecosystem, an unique, fragile, highly productive ecosystem in the sea- land interphase, is the conglomerations of plants, animals and microorganisms acclimatized in the fluctuating environment of tropical intertidal zone. This ecosystem is a highly valued ecosystem in terms of economy, environment and ecology. Mangrove ecosystem of Sundarbans, India, (between 210 32’ – 220 40’ north and between 880 85’ – 890 00’ east) a World Heritage Site, is a unique tidal wetland from the point of view of its biodiversity and ecology. This tidal dominated deltaic complex is the largest of its kind and covers an area of 1,000,000 ha of land and water, the major part (60%) of which is situated in Bangladesh while the remaining western portion (40%) lies within India. The mighty Indian river, the Ganges and its associated estuaries like Muriganga, Saptamukhi, Bidyadhari, Haribhanga, Matla, Thakuran etc open into the Bay of Bengal having a north – south direction of water flow. The silt and loam carried by these estuaries were deposited on the salt marsh eventually leading to the formation of mosaic of 102 deltaic islands of which 54 have been reclaimed for human habitation. A number of geomorphological and resultant hydrological changes have contributed for shapping and reshapping of this estuarine complex making it a very dynamic system. This ecosystem (representing worlds’ one of the most productive ecosystem) harbours thousand of flora and fauna in its diversified habitats and niche. The biodiversity includes true mangrove plants (34 species) and their associate plant species (40), 150 species of algae,163 species of fungi, 32 species of lichen, 250 species of fishes, 7 species of amphibian, 59 species of reptiles, around 200 species of birds, 39 species of mammals, besides numerous species of phytoplankton, zooplankton, ichthyoplankton, benthos, soil inhabiting micro arthropods and mangrove plants dependant insects. Species composition, and their distributional pattern, population dynamics and community structure of different groups of fauna experience wide range of changes spatially and temporally because of the prevailing fluctuating environmental condition. Temperature, rainfall and tidal mixing mostly make this environment unstable with a wide range of variation of major ecological parameters like salinity, pH, dissolved oxygen, nutrients, turbidity etc. from east to west in different periods of year. This ecosystem maintains rural economy by providing timber, fuel wood, faunal resources like fishes, honey etc and protects coast from soil erosion, buffer cyclone, stormes etc, mitigates flood and maintain estuarine flow. However, the biodiversity and basic fabric of ecosystem functioning are being threatened because of several reasons like reclamation of deltaic island for human use, deforestation, erosion and unwanted accretion, salinity invasion, nonjudicious exploitation of fishes, floral and other faunal components, ecotourism, bioinvation and pollution. Further the impact of global climate change has aggreviated the problem. The paper discusses the biodiversity conservation strategies which are being adopted giving due importance to the success and failure of previous ones.