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The northwest coast of the Bay of Bengal and deltaic Sundarbans
Mitra, A. (2000). The northwest coast of the Bay of Bengal and deltaic Sundarbans, in: Sheppard, C.R.C. (Ed.) Seas at the millennium: an environmental evaluation: 2. Regional chapters: The Indian Ocean to The Pacific. pp. 145-160
In: Sheppard, C.R.C. (Ed.) (2000). Seas at the millennium: an environmental evaluation: 2. Regional chapters: The Indian Ocean to The Pacific. Pergamon: Amsterdam. ISBN 0-08-043207-7. XXI, 920 pp., more

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Document type: Review

Keyword
    Marine

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  • Mitra, A.

Abstract
    The Indian Sub-continent lies entirely to the north of the equator with the Tropic of Cancer cutting the country roughly into two halves. About half of the Sub-continent in the northern portion lies outside the Tropics in the mid-latitudes or the Temperate zone. However, the whole of the country is still considered as a tropical country mainly because of its clearly defined isolation from the rest of the Asia by the Himalayan range and the prevalence of a tropical monsoon climate. With a coastline of 7515 km, an exclusive economic zone of 2,014,900 km² and a shelf area of 452,100 km², India occupies a unique position with regard to coastal biodiversity. The eastern, western and southern coasts of peninsular India are replete with majestic rivers which have extensive and highly productive estuarine areas. West Bengal, a maritime state of the northeastern part of the country, adjacent to Bangladesh, is indented in the south by numerous river openings. The important rivers from east to west are the Harinbhanga, Gosaba, Matla, Thakuran, Saptamukhi, Muriganga and Hugli which ultimately terminate in the Bay of Bengal, but on the way encompass approximately 54 islands, criss-crossed and intersected by various creeks and delta distributaries. The deltaic complex at the apex of the Bay of Bengal is the Indian Sundarbans. With a total land and water area of approximately 1,000,000 ha, the entire Sundarbans ecosystem of India and Bangladesh supports the world's largest mangrove block, a well-known ecosystem of the Tropics. Almost 62% of the Sundarbans is situated in Bangladesh, while the remaining 38% -the western sector- lies within India. The Indian Sundarbans, with rich mangrove floral and faunal diversity, swamps and backwaters, form a productive and protective margin for coastal West Bengal. These forest systems are dominated by the salt-tolerant halophytic seed plants that range in size from tall trees to shrubs. There are some similarities in general architecture (e.g. the presence of pneumatophores, cyrptoviviparous seeds or propagules, xerophyllous leaves etc.) and physiology (such as the presence of salt excretory glands or salt regulatory glands). A total of 69 floral species (included within 29 families and 50 genera) have been identified in this ecosystem, out of which 34 species are true mangrove types. These specialised vegetations play an important role in maintaining the economic structure of the coastal population of West Bengal state, as they are the reservoirs of various forestry products ranging from firewood, timber and construction materials for thatching houses, to honey, wax, alcohol, tannins and fisheries. The detritus supplied by this ecosystem to the aquatic phases of the Bay of Bengal and adjacent estuaries provides nutritional input; as a result, the coastal zone of the Bay of Bengal has become a nursery and breeding ground for a large variety of finfish and shellfish. Approximately 70 species of finfish juveniles and 25 species of shellfish juveniles have been recently recorded in the neritic zone of the Bay of Bengal, although a considerable portion of this ecological crop is wasted during the wild harvesting of prawn seeds. This operation is performed by employing nets of special mesh size to screen the seeds of tiger prawn (Penaeus monodon) from the coastal waters. It is needed to meet the growing demands of the large number of shrimp culture farms that have recently sprung up in this part of the Sub-continent. The rapid industrialisation and urbanisation of the cities of Calcutta, Howrah and the newly developing Haldia industrial complex has posed another negative stress to this productive ecosystem: the factories and industries situated on the western bank of the Hugli estuary have significantly contributed to the degradation of this taxonomically diverse ecosystem. As a considerable number of small and large rivers find their way into the Bay of Bengal, a seasonal variation of aquatic salinity and pH is observed. This alters the speciation of compounds present in the marine and estuarine compartments; consequently, the concentrations of several conservative pollutants in the aquatic phase and biological samples oscillate markedly with seasons. Against this background, this chapter discusses the macrofloral and macrofaunal diversity of the coastal region of the Bay of Bengal and the adjacent Sundarbans mangrove ecosystem, along with the various stresses operating in the area.

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