Mangrove Migration

GS: 3 –ENVIRONMENT Conservation, environmental pollution and degradation


Mangroves are tropical trees that thrive in conditions most timber could never tolerate — salty, coastal waters, and the interminable ebb and flow of the tide.


  • In 2008, Punarbasu Chaudhuri, mangrove ecologist from the University of Calcutta spotted an interesting mangrove plant at the bank of river Hooghly inside Kolkata city.
  • Was quite unusual, as mangroves require a cyclic supply of saline water.
  • This growth at an upstream zone was remarkable.

Recently in News:

  • His recent paper suggests that the mangroves have started moving upstream, growing in less-saline regions.


  • Mangroves represent a characteristic littoral (near the seashore) forest ecosystem 
  • Mostly evergreen forests that grow on tropical and subtropical regions( between latitudes 25° N and 25°S)in:
    • sheltered low lying coasts
    • estuaries
    • mudflats
    • tidal creeks backwater
    • marshes 
    • lagoons.
  • Are salt tolerant trees, also called halophytes.(adapted harsh coastal conditions.)
    • Contain a complex salt filtration system.
    • Complex root system to cope with saltwater immersion and wave action.
    • Adapted to the low oxygen (anoxic) conditions of waterlogged mud.
    • Produce pneumatophores (blind roots)
      • to overcome the respiration problem in the anaerobic soil conditions.
    • require high solar radiation to filter saline water through their roots.
      • explains why mangroves are confined to only tropical and sub-tropical regions.
  • Grow below the high-water level of spring tides.
  • The best locations are where abundant silt is brought down by rivers or on the backshaccreting sandy beaches.
  • Adventitious roots which emerged from the main trunk of a tree above ground level are called stilt roots.
  • Variety of configurations.
    • Rhizophora send arching prop roots down into the water.
    • Avicennia send vertical Pneumatophores or air roots up from the mud.
  • Exhibit Viviparity mode of reproduction.
    • seeds germinate in the tree itself.
    • before falling to the ground.
    • adaptive mechanism to overcome the problem of germination in saline water.


  • Are highly productive ecosystems.
    • supports numerous florae, avifauna and wildlife.
  • The trees may vary in height from 8 to 20 m.
  • Protect the shoreline from the effect of cyclones and tsunamis.
  • Are breeding and spawning ground for many commercially important fishes.
  • Represent the best example of ecotone.
  • Moderate monsoonal tidal floods and reduce inundation of coastal lowlands.
  • Prevent coastal soil erosion.
  • Enhance the natural recycling of nutrients.
  • Supply woods, firewood, medicinal plants and edible plants to local people.
  • provide numerous employment opportunities to local communities.
  • augments their livelihood.

Reasons for moving Up-stream:

  • After surveying the banks near Kolkata
    • was able to spot a few mangroves belonging to the genus Sonneratia.
    • have started to redistributed due to:-
      • gradual environmental changes.
      • anthropogenic activities.
  • Marine Pollution Bulletin notes 
    • that mangroves have reclaimed even the upper course of the rivers.
    • also studied the sediments and water samples along the river banks.
    • the rapid growth of Kolkata city, sewage disposal has increased the pollution load in the river waters.
  • Globally – rapid mean sea-level rise.
  • All these factors might have played a role in this upstream migration.- explains Dr. Chaudhuri.(University of Calcutta’s Department of Environmental Science.)

Mangroves in India:

  1. Coringa Mangroves:
  • Recently,  Andhra Pradesh Government has constituted a seven-member committee for fulfilment of norms required for proposing the Godavari Mangroves (Mada forests), at Coringa(CWLS),as a World Heritage Site.
  • are touted to be the second largest mangroves in India.(largest-Sunderbans in West Bengal)
  • located in the estuaries of the Godavari and the Krishna rivers.
  • The Hope Island, a naturally formed sandy stretch amidst the sea that turned into a synonym for biodiversity,comes under the sanctuary.
  • has a site where Olive Ridley Sea Turtle’s nest from January to March every year.
  • Once gets the heritage site tag, UNESCO will help develop tourism and protect the wildlife in the mangroves.
  • Hooghly estuary:
  1. The construction of Farakka Barrage in 1975 has increased fresh water flow in River Hooghly.
    • causing change in ecology and chemistry of the river.
    • high chemical oxygen demand in the river.
      • because of increased release of harmful chemicals from multiple point and non-point sources.

Studies from China:

Sonneratia caseolaris grow well in the presence of high chemical oxygen demand of water.

  1. shows the potential to act as a bio-indicator of regional environmental changes.
  2. They directly indicate 
    • Changes in the micro-environment.
    • The rate of sedimentation
    • Quality of the sediment
    • Biogeochemistry of the river 
  3. has all been affected by elevated anthropogenic activities and global climate change events.

Way Forward

  • The team saw that between Barrackpore and Birlapur, in a non-saline region, about 239 mature trees and numerous saplings of Sonneratia caseolaris have grown naturally.
  • More studies are needed to understand in detail this new horizon of mangrove adaptation and dispersion ecology.
  • Also have to plan to study more rivers in this region to get a detailed picture of this migration.


       The decline in the mangrove area along with this up stream less saline areas migration may increase the amplitude of coastal hazards such as storm surges, erosion and flooding.

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