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Sundarbans Mangroves: Freshwater Species of the Week

Mangroves anchor the edges of the world, but they are slipping away, thanks to coastal development, pollution, over-harvesting, nutrient loading, overuse of freshwater, and climate change.

The world’s largest intact halophytic (salt-tolerating) mangrove forest is the Sundarbans, a UNESCO World Heritage Site that straddles India and Bangladesh. It forms the transition zone between the Ganges and the Bay of Bengal, and is a stronghold for the endangered Bengal tiger, as well as many other species, from monkeys to crocodiles.

The Sundarbans are dominated by Sterculiaceae and Euphorbiaceae mangroves, which are less common in most of the rest of the world. These include Sundari (Heritiera fomes) and looking-glass (Heritiera littoralis) mangroves. The hard wood of the latter was long used in boat building.

However, as a recent report by Dr. Md. Mizanur Rahman warns, these mangroves are in trouble. They face rising temperature, rising seas, silt and pollution washing down from deforested areas in the Himalaya, and pressures from aquaculture activities around the Sundarbans.

They are also being assaulted by rising salinity, brought by the formerly fresh rivers and streams that feed them. As agriculture increases in the region, water levels drop, minerals accumulate, and salinity rises. Brackish water is also expanding underground.

“Predictions from Sundarbans territory show that salinity may be double over the next few decades posing risks for survival of flora in Sundarbans,” writes Rahman.

He continued, “Natural vegetations of such areas are being destructed causing major changes in landscapes and biodiversity. Destruction of remaining natural habitats in core areas, buffer zones and corridors are also occurring. Most of the coastal districts already face severe salinity problems, with saline water pushing up to 250 km inward during the dry season.”

According to Rahman, Sundari trees and nypa palms are declining, changing the makeup of the ecosystem.

He added, “A salt concentration of 20-40% is suitable for mangrove ecosystems, while 40-80% diminishes the number of species and their size. Only a few species can exist and grow in 90% salt concentration. Sundari, Bain, Kakra, Passur and Dhondul tree species are being quickly replaced by Gewa and Keora.”

The fate of the Sundarbans mangroves lies both in how they can be protected locally, and in the health of the whole Ganges system. What happens upstream affects what comes down the pike.

Learn more about the world’s river basins, and how they affect us.


Brian Clark Howard is a writer and editor with He was formerly an editor at The Daily Green and E/The Environmental Magazine and has contributed to many publications, including,,,, Yahoo!, MSN and elsewhere. His latest book, with Kevin Shea, is Build Your Own Small Wind Power System.


  1. Varghese Kidangalil
    Kulasekharam, Tamil Nadu, India
    October 21, 2013, 8:09 am

    There seems to be a mix up between ppt and percentage. It’s not 20-40%, but 20-40 ppt (parts per thousand)

  2. Dr. Md. Mizanur Rahman
    Mongla, Bangladesh
    May 10, 2012, 2:10 pm

    Dr AssafRosenthal,
    Soil salinity is few times higher than the salinity of sea water due to evaporation and drought. My statements are supported by many scientists like Professor Phan Nguyen Hong, Director, Mangrove Ecosystem Research Centre, Hanoi National Pedagogic University. “nothing grow in salt concentration over 12%”, is it correct? Moderately halophilic bacteria grow optimally in the media containing 0-20% salt concentration (Li et al., 2012).

  3. Don Belt
    Reston, VA
    May 10, 2012, 1:35 pm

    FYI, there’s more about the Sundarbans in my recent National Geographic magazine piece about Bangladesh here:
    Don Belt

  4. erin livan
    May 8, 2012, 4:34 pm

    cocnuts,able live coastal,companion plant,roots form mass,keeps dunes together,salt threshold??must absorb salt,withstands cyclones,.multi-function tree,,

  5. [...] To see photos and the original report please click [...]

  6. dr kazi rezaul ahsan
    dhaka, bangladesh
    May 5, 2012, 10:56 am

    This report states in part about the effect of change in upstream of ganges. But there is something I want to add. Indian legislators are thinking about a inter river joining project which they will use to hold the natural flow of water from Himalayas. This I think, will further endanger the ecosystem of Sundarban. Though its a political issue, I hope NG should arrange a team to cover this matter and raise a worldwide awareness aout the issue.

  7. Dr AssafRosenthal
    Eilat - Israel
    May 5, 2012, 7:04 am

    “A salt concentration of 20-40% is suitable”…… ” Only a few species can exist and grow in 90% salt concentration”….
    Wrong ! nothing grow in salt concentration
    over 12% , The concentration in ocean is 3.5% , concentration of salt’s in the
    Dead-sea is 35%
    Wrong ! Wrong ! Wrong !

  8. khaled
    May 5, 2012, 5:19 am

    Nice report on South Asian biodiversity .

  9. [...] Sundarbans Mangroves: Freshwater Species of the WeekNational GeographicMangroves anchor the edges of the world, but they are slipping away, thanks to coastal development, pollution, over-harvesting, nutrient loading, overuse of freshwater, and climate change. The world's largest intact halophytic (salt-tolerating) …and more » [...]