Loss of Mangrove Cover on Katchal Island
Source: DTE
GS III: Environment and Conservation

What is discussed under Loss of Mangrove Cover on Katchal Island?

1. What is mangrove cover?
2. About mangrove cover in India 
3. Key highlights of the study
4. Mangroves in Katchal island

Why in News?

NASA highlights the loss of mangrove cover on Katchal island in India’s Nicobar archipelago.

Key Facts

The Indian Ocean Tsunami destroyed more than 90% of the island’s mangrove forests.

What is Mangrove Cover?

• • Mangrove forests are found in tidal areas in the tropics and subtropics.
  • The word ‘mangrove’ may refer to the habitat as a whole or to the trees and shrubs in the mangrove swamp.
  • Mangroves can be found in estuaries and along ocean shorelines.

Special features of mangroves

• • Saline environment:

    

    • They can thrive in adverse environments with high salt and low oxygen levels.
    • When mangrove trees come into touch with salty or brackish water, their unique salt filtration system and root system filter out 90% of the salt. 
  • Low oxygen:
    • Black mangroves are adaptable to low oxygen, breathing through specialized root-like structures called pneumatophores
  • Viviparity:
    • Mangrove seeds are floating, making them ideal for water distribution.
    • Red mangroves are viviparous, which means their seeds germinate while still connected to the parent tree.
    • Once germinated, the seedling develops either within the fruit or out through the fruit to create a  ready-to-go seedling that can provide its own nourishment through photosynthesis.

Benefits of mangrove forests to the environment

• • Contributing to the long-term sustainability of coastal and marine ecosystems
  • Protecting adjacent regions from tsunamis and other severe weather occurrences
  • Carbon sequestration storage and climate change mitigation
  • Assist local ecosystems in adapting to changes such as intense weather and sea level rise

Global Mangrove Cover

• • The overall global mangrove cover is 1,50,000 sq km.
  • Asia has the most mangroves in the world followed by Africa, North and Central America, Oceania and South America.
  • South Asia accounts for 6.8% of the global mangrove cover.

Mangrove Cover in India

• • India’s contribution is 45.8% total mangrove cover in South Asia.
  • Mangrove cover in India is 4992 sq. Km which is 0.15% of country’s total geographical area.
  • The deltas of the Ganges, Mahanadi, Krishna, Godavari, and the Cauveryrivers contain mangrove forests.
  • The backwaters in Kerala have a high density of mangrove forests.
  • Sundarbans in West Bengal is the largest mangrove forest regions in the world.
  • The second largest mangrove forest in India is Bhitarkanika

About Katchal Island

• • The Katchal Island is the largest Island among all the other Nicobar Islands and was comprised of 35 villages prior to the Tsunami.
  • The Island of Katchal, was earlier referred to as ‘Tihnyu’ in the local language.
  • It is approximately 1,600 km away from mainland (India) and 305 km south to capital Port Blair.
  • The hills of Katchal are composed of calcareous sandstone and marble slates.
  • To stop the economic exploitation of the islanders, the Government of India declared the Nicobar Islands an Aboriginal Tribal Reserve Area (ATRA) on 2 April 1957.

Key Highlights of the Study

• • The United States National Aeronautics and Space Administration (NASA) highlighted a study that revealed the degree to which mangroves have been destroyed globally during the previous two decades.
  • The islands underwent up to 3 metres (10 feet) of land subsidence following the magnitude-9.2 Aceh-Andaman earthquake in December 2004.
  • Many mangrove habitats were drowned as a result, with some regions losing more than 90% of their mangrove extent.

Tidal wetlands  

• • High-resolution mapping of losses and gains of Earth’s tidal wetlands found that 4,000 square kilometres of tidal wetlands were lost between 1999 and 2019.
  • Outside of Asia, tidal wetlands in Africa had the greatest loss-to-gain ratio. The loss was higher in Nigeria, Mozambique, and Guinea-Bissau.
  • Mangroves had the highest ratio of loss to gain among the three types of tidal wetlands (tidal flats, marshes and mangroves) it studied. 

Mangroves in Katchal island

• • The NASA Earth Observatory displayed a satellite-shot map of Katchal Island which shows tidal wetland erosion in orange colour from 1999 to 2019.
  • The mangrove cover on Katchal will not come back. But in other places, mangroves have reappeared since they propagate themselves through propagules.
    • Propagule: A vegetative structure that can become detached from a plant and give rise to a new plant. Examples include a bud, sucker, or spore.

Reasons for loss of mangroves

• • Natural cause:
    • The earthquake in 2004 during Tsunami resulted in land subsidence in the islands up to 3 meters (10 feet), which submerged many mangrove ecosystems, resulting in a loss of more than 90% of mangrove extent in some areas.
    • Other causes of wetland change were:
      • sea level rise
      • shoreline erosion
      • storms
      • altered sediment flow and subsidence

• • Human activity:
    • Human induce was directly responsible for around 27% of the losses and gains, as humans affect wetlands through construction, water diversion projects, or conversion of land to cultivation or aquaculture.

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