Threatened Mangroves of Sunderbans

S.R. Gupta and Arun Lekha

Mangroves are taxonomically diverse group of salt tolerant, broad-leaved evergreen trees and shrubs that grow primarily in tropical and subtropical coastal regions of Asia, Australia and America. Mangroves are made up of salt tolerant evergreen trees and act as natural buffers against tropical cyclones. Mangroves have special aerial roots, prop roots and buttresses to live in muddy, shifting and saline conditions. Theses mangrove systems are the nurseries of many invertebrate species and fish. The Sundarban Mangrove forest, covering an area of 16,000 km2 of land and water, is the longest mangrove forests in the world. Sundarban mangrove lies within the delta of the Ganges, Brahamputra and Meghna rivers in the Bay of Bengal; 60% of the area lies in Bangladesh and 40% area in India. It is a biosphere reserve and the core area (Sundarban National Reserve) is world Heritage site. Under the project Tiger, the Government of India has established a Tiger Reserve in Sundarban.

The Sunderbans Mangrove harbours a rich biodiversity of plants and animals, and is the only habitat for the endangered Royal Bengal Tiger. There is great abundance of invertebrates, birds, insects, monkeys and reptiles. The mangrove ecosystem provides income to the local people from the collection of mollusks, crustaceans, fish and honey. A large number of species of prawns and shrimps are exploited commercially. According to IPCC report 2007, sea level rise is the greatest threat to the Sundarban mangrove system because of flooding of low-lying delta, retreat of shoreline, saliniztion and acidification of soil, changes in water table and adverse effect on livelihood of local people. Mangrove will be affected greatest by sea-level rise. In the case of a 45cm rise in global sea level will cause a destruction of the 75% of the Sundarbans mangrove. Some climate change models also predict increased frequency of tropical cyclones in coastal regions that will impact the biodiversity and resilience of the mangroves.


POSSIBLE CLIMATE CHANGE IMPACT ON MANGROVES


Possible Impact
Temperature Increase
Change in seasonal patterns of reproduction of plants and animals
Elevated CO2
May cause species specific variations
Sea- level changes
Decrease in geographic distribution
Change in species composition
Change in species diversity of mangroves on small islands

Tropical storms
Increased frequency and intensity of storms will affect salinity levels, flooding of low lying areas and wetland sediment budget
Precipitation Change
Effect on plant growth and aerial extent


Sources:
IPCC (2007), and Brij Gopal and Malavika Chauhan(Aquatic sciences, 2007)