Declining Mangrove Cover

In News

• Recently, NASA has highlighted the loss of mangrove cover on Katchal island, a part of India’s Nicobar archipelago.

Key Findings

• Loss of Mangroves: 
  • The study showed the extent to which mangroves had been lost globally over the past two decades.
• The NASA Earth Observatory showed a map of the island August 8, 2022, shot from a satellite. It depicted tidal wetland loss from 1999 through 2019 in orange color.

Image Courtesy: DTE 

• Earthquake’s impact: 
  • After the Andaman earthquake in December 2004, the islands experienced up to 3 meters (10 feet) of land subsidence. This submerged many mangrove ecosystems, resulting in a loss of more than 90 percent of mangrove extent in some areas.
• Tidal wetlands:
  • 4,000 square kilometers of tidal wetlands were lost between 1999 and 2019.
  • Mangroves had the highest ratio of loss to gain among the three types of tidal wetlands. The other two were tidal flats and marshes.
  • Mangroves showed an estimated net decrease of 3,700 square kilometers between 1999 and 2019.
  • A net loss of tidal wetlands on deltas globally, though gains of 2,100 square kilometers alongside losses of 2,300 square kilometers indicate the considerable dynamism of these systems.
  • Outside of Asia, tidal wetlands in Africa had the highest ratio of loss to gain. The loss was most severe in Nigeria, Mozambique and Guinea-Bissau.
• Causes of wetland change:
  • Anthropogenic activities
  • Sea level rise, 
  • Shoreline erosion, 
  • Storms, 
  • Altered sediment flow and 
  • Subsidence. 

Mangroves

• A mangrove is a small tree or shrub that grows along coastlines, taking root in salty sediments, often underwater. 
• Mangroves are flowering trees, belonging to the families Rhizophoraceae, Acanthaceae, Lythraceae, Combretaceae, and Arecaceae.
• The upper trunk, including the branches and leaves, of a mangrove tree, lives completely above the waterline, while the lower trunk and the large root system are partly covered by seawater. 
• Many species have roots diverging from stems and branches and penetrating the soil some distance away from the main stem (like banyan trees).
• Features:
  • Saline Environment: A speciality of mangroves is that they can survive under extreme hostile environments such as high salt and low oxygen conditions.
    • Mangrove trees contain a complex salt filtration system and complex root system to cope with saltwater immersion and wave action. 
    • The roots filter out 90% of the salt they come into contact with within the saline and brackish water they call home. Some species of mangrove excrete salt through glands in their leaves.
  • Low oxygen: Underground tissue of any plant needs oxygen for respiration. But in a mangrove environment, the oxygen in soil is limited or nil.
    • Hence the mangrove root system absorbs oxygen from the atmosphere.
    • Mangroves have special roots for this purpose called breathing roots or pneumatophores.
      • These roots have numerous pores through which oxygen enters the underground tissues.
  • Store Freshwater: Mangroves, like desert plants, store fresh water in thick succulent leaves. A waxy coating on the leaves seals in the water and minimizes evaporation.
  • Mangroves are viviparous: Their seeds germinate while still attached to the parent tree. Once germinated, the seedling grows into a propagule. 
    • The mature propagule then drops into the water and gets transported to a different spot, eventually taking root in a solid ground.

Distribution of Mangroves 

• Mangroves can be found in over 118 countries and territories in the tropical and subtropical regions of the world. 
  • Asia has the largest coverage of the world’s mangroves, followed by Africa, North and Central America, Oceania and South America. Approximately 75% of the world’s mangrove forests are found in just 15 countries.
• In India:
  • The deltas of the Ganges, Mahanadi, Krishna, Godavari, and the Cauvery rivers contain mangrove forests. 
  • The backwaters in Kerala have a high density of mangrove forest.
  • The Sundarbans in West Bengal is the largest mangrove region in the world and a UNESCO World Heritage Site. It spans from the Hooghly River in West Bengal to the Baleswar River in Bangladesh.
  • The Bhitarkanika mangrove system in Odisha is India’s second-largest mangrove forest. 
  • Pichavaram in Tamil Nadu has a vast expanse of water covered with mangrove forests. It is home to many aquatic bird species.

Importance of Mangroves

• Natural Barriers: Mangrove forests act as natural barriers against storm surge, coastal flooding and sea-level rise. Their intricate root system stabilizes the coastline, reducing erosion from storm surges. Together with the tree trunks, they work like speed-breakers to slow down the tides.
• Filters Water: Mangrove thickets maintain water quality by filtering pollutants and trapping sediments originating from land.
• Habitat Provider: They provide habitat for a diverse array of terrestrial organisms. Their branches provide homes for lizards, snakes and nesting birds. Many species of coastal and offshore fish and shellfish rely exclusively on mangroves as their breeding, spawning, and hatching grounds.
• Powerhouses: Mangroves also have a big impact on climate. Mangroves are powerhouses when it comes to carbon storage. Studies indicate that mangroves can sequester (lock away) greater amounts of carbon than other trees in the peat soil beneath. They store this carbon for thousands of years.
• Sources of Livelihood: Many people living in and around mangroves depend on them for their livelihood. The trees are a source of wood for construction and fuel. The ecosystem provides local fishermen with a rich supply of fish, crabs and shellfish. The ecosystem also supports tourism.

Major Threats

• Coastal development, including the construction of shrimp farms, hotels, and other structures, is the primary threat to mangroves.
• Mangrove forests are cleared to make room for agricultural land and human settlements.
• Mangrove trees are used for firewood, construction wood, charcoal production, and animal fodder. In some parts of the world, there has been overharvesting which is no longer sustainable.
• Overfishing, pollution, and rising sea levels are the other threats to mangrove forests and their ecosystem.
• Scientists estimate that at least one-third of all mangrove forests have been lost during the last few decades.

Way Ahead

• The mangroves have a crucial role in sustaining and preserving the coastal ecosystem. 
• Efforts need to be taken to compensate for the plants that are damaged due to various natural and anthropogenic activities with proper plantation drives.

Source: DTE