[Answered]Discuss the causes of depletion of mangroves and explain their importance in maintaining coastal ecology.

 Mangroves are salt-tolerant vegetation that grows in intertidal regions of rivers and estuaries. They are referred to as ‘tidal forests’ and belong to the category of ‘tropical wetland rainforest ecosystem’. Mangrove forests occupy around 2,00,000 sq km across the globe in tropical regions of 30 countries. India has a total mangrove cover of 4,482 sq km. However, more than 35% of the world’s mangroves are already depleted. A scientific study reported that 100% of mangrove species, 92% of mangrove associates are under threat.

Causes of Depletion of mangroves:

1. Sea level rise and coastal erosion: Due to global warming, the sea levels are continuously rising. The rising sea levels have flooded large areas of mangrove forests. This has resulted in their depletion. This has been supplemented by continuous erosion by sea towards the land.
2. Reduction in river water levels: The mangroves are more prevalent in areas where the rivers meet the sea. The system requires a fine balance between salt and sweet water to survive. Reduction of river water due to dams has caused destruction of mangroves.
3. Invasion by alien species:Introduction of non-native and alien species of plants and animals are causing threat to the endemic species of the region. This has led to an imbalance in ecological structure, resulting in their depletion.
4. Clearing:Large tracts of mangrove forests have been cleared to make room for agricultural land, human settlements, industrial areas, shrimp aquaculture etc. As a result, mangroves get depleted to the tune of 2-8 percent annually.
5. Over harvesting:They are also overexploited for firewood, construction wood and pulp production, charcoal production, and animal fodder.
6. Damming of rivers: Dams built over the river courses reduce the amount of water and sediments reaching mangrove forests, altering their salinity level.
7. Destruction of coral reefs:Coral reefs provide the first barrier against currents and strong waves. When they are destroyed, even stronger-than-normal waves reaching the coast can wash away the fine sediment in which the mangroves grow.
8. Pollution: Mangroves also face severe threats due to fertilisers, pesticides, discharge of domestic sewage and industrial effluents carried down by the river systems.
9. Climate change:Unusually low rainfall and very high sea surface and air temperatures caused severe threats to the survival of mangrove forests. 

Importance of mangroves in maintaining coastal ecology:

1. Edge Effect: The mangroves show edge effect, which means that they have large species diversity in comparison to marine or terrestrial ecosystem.
2. Productivity: Mangroves are among the most productive terrestrial ecosystems and are a natural, renewable resource. For instance, Sundarbans in the Gangetic delta supports around 30 plant species of mangroves.
3. Ecological Niches: Mangroves provide ecological niches for a wide variety of organisms. They serve as breeding, feeding and nursery grounds for fisheries and provide timber and wood for fuel.
4. Natural Filters: Mangrove forests act as water filters and purifiers as well. When water from rivers and floodplains flow into the ocean, mangroves filter a lot of sediments, hence protecting the coastal ecology including coral reefs.
5. Resource: They supply timber, firewood, medicinal plants and edible plants to local people.
6. Employment: They provide numerous employment opportunities to local communities and augment their livelihoods.
7. Shock absorbers: Mangroves act as shock absorbers. They reduce high tides and waves and protect shorelines from erosion and also minimise disasters due to cyclones and tsunami.

Given their importance, strict enforcement of the coastal regulation measures, scientific management practices and participation of the local community in conservation and management are essential for the conservation and sustainable management of the precious mangrove forests. The mangroves have an important role in sustaining and preserving coastal ecosystem. The threats posed by human activities can upset the natural balance and cause their depletion.