Encyclopedia of Earth

Sundarbans mangroves

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Mangrove habitat near Bombay, India. Photographer: Mauri Rautkari, WWF

The Sundarbans mangroves ecoregion is the Earth's most extensive mangrove ecosystem. Named after the dominant mangrove species present in this ecoregion, Heritiera fomes, locally known as sundri, this is the single mangrove ecoregion that harbours the Indo-Pacific region's largest predator, the Tiger (Panthera tigris).

Unlike in other habitats, here Tigers live and swim among the mangrove islands, where they hunt scarce prey such as Chital Deer (Axis axis), Indian Muntjac deer (Muntiacus muntjak), Wild Boar  (Sus scrofa), and even the Rhesus Macaque (Macaca mulatta). Sometimes, the people who venture into these almost impenetrable forests fall victim to the tigers, as they seek to gather honey, to fish, and to cut mangrove trees in order to make charcoal.

But the ecoregion's importance is not based solely on its role as a priority Tiger conservation area. Mangroves are a transition from the marine to freshwater and terrestrial systems. They provide critical habitat for numerous species of fishes and crustaceans that are adapted to live, reproduce, and spend their juvenile lives among the tangled mass of roots, known as pneumatophores, that grow upward from the anaerobic mud to respire a supply of carbon dioxide.

Location and General Description

caption Source: WWF

The ecoregion lies in the vast delta formed by the confluence of the Ganges, Brahmaputra, and Meghna rivers. The maze of mangrove channels extends across southern Bangladesh and the West Bengal State of India. The June to September monsoon regularly brings heavy rains and frequent devastating cyclones that cause widespread destruction. Annual rainfall can exceed 3500 millimeters (mm), and daytime temperatures can exceed a stifling 480C during these monsoon months.

Mangroves are not biologically diverse compared with most other terrestrial ecosystems. The undisturbed forests have an unstratified, dense canopy and an undergrowth made up of seedlings and saplings of the canopy trees. In the Sundarbans, the mangrove forests are characterized by Heritiera fomes, a species valued for its timber. Other species that comprise the forest assemblage include Avicennia spp., Xylocarpus mekongensis, X. granatum, Sonneratia apetala, Bruguiera gymnorrhiza, Cereops decandra, Aegiceras corniculatum, Rhizophora mucronata, and the Nipa Palm (Nypa fruticans).

caption Source: WWF

Biodiversity Features

This vast mangrove ecosystem along the marine, freshwater, and terrestrial interfaces provides critical ecosystem functions. The tangled mass of roots from mangrove trees provides safe havens for juvenile stages of a gamut of species, from fish fry to shrimp naupleii.

The ecoregion harbors several mammals, but the most charismatic undoubtedly is the majestic Bengal Tiger that swims from island to mangrove island searching for and hunting scarce prey. Because this ecoregion represents the only example of tigers ecologically adapted to a life in the mangroves, it has been designated a Level I TCU. The tiger's reputation as a human-eater is greater here than anywhere else in its range; the people who venture into the Sundarbans must take great precautions to avoid being attacked. One fascinating deterrent is wearing a mask in the back of the head because the Tiger is thought to be less likely to attack a human looking directly at him.

Several other predators dwell in this labyrinth of channels. Two species of crocodiles (Crocodylus porosus and C. palustris), the Gangetic gavial (Gavialis gangeticus), and the water Monitor lizard (Varanus salvator) use both land and water to hunt and bask in. Sharks and the Gangetic freshwater dolphins (Platanista gangetica) inhabit the waterways. And several birds of prey patrol the sky overhead. More cryptic and equally fascinating are the mudskippers, a gobioid fish that climbs out of the water into mudflats and even climbs trees. An abundance of crabs, hermit crabs, and shrimp scavenge among the roots.

More than 170 bird species are known to inhabit these mangrove forests, including a single endemic species (table 1). This brown-winged kingfisher is limited to the coastal habitats in this ecoregion.

 Table 1. Endemic and Near-Endemic Bird Species.

Family

Common Name

Species

Alcedinidae

Brown-winged Kingfisher

Pelargopsis amauropterus*

Asterisk indicates that the taxon range is limited to this ecoregion.

The bird assemblage also includes the globally threatened Lesser Adjutant Stork (Leptoptilos javanicus) and threatened Masked Finfoot (Heliopais personata). There are twelve birds of prey that cohabit within this ecoregion, including the Osprey (Pandion haliaetus), White-bellied Sea Eagle (Haliaeetus leucogaster), and Grey-headed Fish-eagle (Ichthyophaga ichthyaetus). The mangrove ecosystem also is an important staging and wintering area for migratory birds, which include several taxa of shorebirds, gulls and terns.

Current Status

Bangladesh supports one of the world's highest human population densities. About half of this ecoregion's mangrove forests have been over-harvested to supply the fuelwood and other natural resources extracted from these forests by this high human population density. Despite the intense and large-scale exploitation, the ecoregion remains one of the largest contiguous areas of mangroves on Earth.

There are seven protected areas that cover almost 2700 square kilometers (km2), or 15 percent of the ecoregion (table 2). Despite the high proportion of the ecoregion being within the protected area system, only one of these, Sajnakhali, is large enough to support a space-dependent species such as the tiger. Many of the protected areas also lack trained and dedicated personnel and infrastructure to adequately manage them.

 

 Table 2. Protected Areas That Overlap with the Ecoregion.

Protected Area

Area (km2)

IUCN Category

Sajnakhali

2,090

IV

Sundarbans East

210

IV

Char Kukri-Mukri

30

IV

Sundarbans South

200

IV

Sundarbans West

130

IV

Halliday Island

4

IV

Lothian Island

20

IV

Total

2,684

 

 

Types and Severity of Threats

The conservation status of the ecoregion was changed from vulnerable to endangered because of the projected human threats. The human population in the Sundarbans, now estimated at more than two million, continues to increase very rapidly. Hunting and trapping wildlife, cutting and lopping trees for fuelwood and to make charcoal, and overexploiting the trees for timber by the forestry industry are some of the most severe current threats. Shrimp fry are being collected at unsustainable levels to supply the shrimp grow-out industry, and the mangrove forests are cut and cleared to build shrimp grow-out ponds, contributing to habitat degradation and habitat loss. There is also the potential for harmful effluents to enter the mangrove waterways from a proposed fertilizer plant.

But some of the greatest threats to this ecoregion's biodiversity emanate from thousands of kilometers away. The rivers that feed and flush the mangroves bring down heavy silt loads as a result of deforestation and erosion in the Himalayan Range. This silt and water turbidity have profound effects on the sensitive mangrove ecosystem and its flora and fauna, especially on the juvenile stages that the mangroves support. The diversion of more than 30 percent of the Ganges River's dry season flow through the Farraka Barrage in India to provide irrigation for agriculture has dramatically increased salinity levels and disrupted fish migration and breeding patterns. The delicately balanced community composition in these mangroves is determined to a large part by salinity levels.

Protected Areas

A substantial portion of this ecoregion has been designated as a World Heritage Site. The total area of the Bangladesh section of Sundarbans is 595,000 hectares (ha) of which 139,699 hectares are protected as follows: Sundarbans West Wildlife Sanctuary with 71,502 hectares; Sundarbans East Wildlife Sanctuary with 31,226 hectares; and Sundarbans South Wildlife Sanctuary with 36,970 hectares. Sundarbans National Park (133,010 hectares), a World Heritage Site, is situated to the west in India.

This article was reviewed and approved by topic editor Mark McGinley

References

  • Blower, J. (1985). Sundarbans Forest Inventory Project, Bangladesh. Wildlife conservation in the Sundarbans. Project Report 151. Overseas Development Administration, Land Resources Development Centre, Surbiton, UK. 39 pp.
  • Chaffey, D. R. and Sadom, J.H. (1985). Sundarbans Forestry Inventory Project. A glossary of vernacular plant names and a field key to trees. Overseas Development Administration, Land Resources Development Centre, Surbiton, UK. 23 pp.
  • Champion, H. G. (1936). A preliminary survey of the forest types of India and Burma. Indian Forest Record (New Series) 1: 1-286.
  • Choudhury, A. M. (1968). Working plan of the Sundarban Forest Division for the period from 1960-61 to 1979-80. Vol. I. Government of East Pakistan, Forest Department, Dacca. 82 pp.
  • Christensen, B. (1984). Ecological aspects of the Sundarbans. FO: TCP/BGD/2309 (Mf). FAO, Rome.
  • Sarker, S. U. and Sarker, N. J. (1986). Status and distribution of birds of the Sundarbans, Bangladesh. The Journal of Noami 3: 19-33.
  • Scott, D. A. (Ed.) (1989). A Directory of Asian wetlands. IUCN, Gland, Switzerland and Cambridge, UK. 1,181 pp. ISBN: 2880329841.
  • Seidensticker, J. and Hai, M. A. (1983). The Sundarbans Wildlife Management Plan: conservation in the Bangladesh coastal zone. IUCN, Gland, Switzerland. 120 pp.
  • Siddiqi, N. A. and Choudhury, J. H. (1987). Man-eating behaviour of tigers (Panthera tigris Linn) of the Sundarbans - twenty-eight years' record analysis. Tigerpaper 14(3): 26-32.

Disclaimer: This article contains some information that was originally published by the World Wildlife Fund. Topic editors and authors for the Encyclopedia of Earth have edited its content and added new information. The use of information from the World Wildlife Fund should not be construed as support for or endorsement by that organization for new content added by EoE authors, or for editing of the earlier content.

 

 

 

 

 

 

 

 

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Citation

Fund, W., & Hogan, C. (2013). Sundarbans mangroves. Retrieved from http://www.eoearth.org/view/article/51cbeefa7896bb431f69b96c