- Mangroves have multiple ecosystem services including carbon sequestration, flood mitigation, protection against wind and waves, fisheries and habitat for biodiversity.
- However, India’s coastal cities have lost large swathes of mangrove cover, leaving them vulnerable to sea level rise, flood events, storm surges and cyclones.
- Maintaining existing stands is equally important as replanting mangroves in other locations, as mature forests offer better coastal protection than do young mangrove forests.
Dependable, sturdy and rich in biodiversity, mangroves form the final frontier between the land and the sea. Their branching root systems protrude from the gentle ebb and flow of the tides, and their presence ensure the presence of specialised endemic wildlife. However, despite their many contributions towards the wellbeing of human and non-human species, mangroves remain threatened by habitat loss, rising sea level, climate change and anthropogenic pressures.
Mangroves are shrubs or trees that grow in brackish water, where saline sea water meets freshwater. Often, these short trees are found in the inter-tidal zone, where their complex root systems allow them to breathe despite waterlogged conditions and stabilise the ever-shifting soil. These are species that preferentially grow in an equatorial climate and unlike most other tree species, mangroves have adapted to shifting levels of salinity. These forests of land and sea are some of the most productive wetlands, known in particular for their plethora of ecosystem services and their high biodiversity.
There are over 70 known species of mangroves and different species have varying tolerances towards salinity. This leads to a phenomenon known as zonation, where more salt-tolerant species form the first line of defence against the tide, while those that prefer a less saline environment congregate towards the freshwater inflows. High salinity is typically associated with reduced species diversity. A near-constant push and pull is the result; sometimes, mangrove forests are broad and span many kilometres while in other ecoregions, they may be deeply incised into the delta or estuary with minimal spread.
India is home to the world’s largest mangrove swamp forest, the Sundarbans, an immense delta straddling the Indian state of West Bengal and Bangladesh over 10,000 sq. km. The Sundarbans covers 43 percent of India’s mangrove cover singlehandedly, followed next by the mangroves of the Kachchh coastline in Gujarat (23 percent). Major mangrove blocks in India include the Deltaic (east coast) mangroves, Non-Deltaic (west coast) mangroves, and Island mangroves.
Mangrove cover in the east coast is higher than that of the west coast, largely due to the broad river deltas formed by the Ganga, Brahmaputra, Godavari, Mahanadi, Krishna and Kaveri rivers. The west-flowing rivers of India traverse a shorter distance, thus depositing less sediment at their mouth and creating smaller, narrower estuaries rather than the wide-mouthed deltas of the western coastline. Hence, mangrove cover is less on the west coast of the country, with notable exceptions existing in Maharashtra and Gujarat in the wetlands formed by the Narmada and Tapti rivers. Apart from having the third largest area of mangrove forest globally, India has the highest record of species richness with 4107 known species, which encapsulate 925 plant species and 3182 animal species.
How do mangroves impact human wellbeing?
Mangroves are an important source of food and livelihoods for local communities, especially for the aquaculture industry. According to the IUCN, aquaculture is considered the fastest growing food-producing sector in the world. Mangroves serve as nurseries for many fish species, and without them, nearly 80 percent of the global fish catch would be directly or indirectly impacted. Other food products sourced from mangrove forests include honey, fruit, salt, leaves, medicinal herbs, and algae, as documented by the Indian Council of Forestry Research and Education, Dehradun.
Known as the dancing trees of the sea, mangroves are regularly buffeted by cyclonic winds, especially along the eastern coast of India, but their intertwined breathing root system holds them firm and retains soil during extreme weather events. Estimates show that mangroves reduce wave height by 31 percent, protecting homes, property and infrastructure from flood events. An example of this is the 2004 Indian Ocean Tsunami. The Pichavaram mangroves lining the coastline of Cuddalore district, Tamil Nadu, protected nearly 1700 people living between 100 to 1000 metres inland from the worst impacts of the tsunami, saving crores of rupees in damage and many human and non-human lives. This mangrove forest also proved valuable in protecting coastal hamlets during Cyclone Gaja (2018), as explained in this article in The Hindu. Such events have lent mangroves the title of a ‘bio shield’ by international governments and contributed towards mitigating their destruction.
“The stabilising services mangroves provide have become a sharp focus in recent years,” says Priyanjana Pramanik, an independent researcher working on mangrove restoration. “Several studies have found that healthy mangroves can save human lives, protect property and prevent damage to coastal zones. As the effects of climate change become more apparent through increasingly frequent extreme weather events such as cyclones, the buffering role of these coastal forests will become more important – as much as 40% of the world’s population is thought to live within 100 km of a coastline, about 1 in 10 people live less than 10m above sea level.”
However, the presence of mangroves alone cannot protect coastlines; older mangrove forests have been found to be more effective in preventing destruction than younger mangroves. Density of the forest and individual tree girth (diameter at breast height) also matter.
Coastal metropolises are losing their mangroves
Traditionally, Indian metropolises have formed along the country’s lengthy coastline, with commercial hotspots such as Mumbai, Chennai, and Kolkata as examples. Mumbai is one of the most densely populated cities in the world, and also intensely vulnerable to climate change-related hazards including sea level rise, coastal erosion, flooding, and storm surge. 24 percent of the city currently constitutes vulnerable land.
Once comprised of seven interconnected islands, extensive land reclamation – the process of dredging soil from the sea – has expanded Mumbai’s footprint rapidly, with many hectares of mangrove forest lost in the process. Additional waste generation from a rising population has led to copious dumping within and around the city’s creeks and rivers, choking waterbodies and impacting the mangroves that line these streams, as described in a 2014 study.
Recently, the Bombay High Court granted permission to the City and Industrial Development Corporation (CIDCO) of Maharashtra to cut 3,728 mangroves for construction of the Ulwe coastal road connecting Mumbai’s Trans Harbour Link to Navi Mumbai. Additional mangrove cover is slotted to be removed for further developmental projects. While the government has assured environmental groups that for every tree cut, a mangrove sapling will be planted at a designated location, research has shown that nascent mangrove forests cannot provide the same ecosystem services as mature forests, especially when encountering rising tides. Apart from preventing flooding, Mumbai’s mangroves prevent soil erosion, maintain the local climate and reduce the Urban Heat Island Effect and sequester atmospheric carbon. However, according to the State of India’s Forests 2020 report, while Mumbai City did not lose mangrove cover from 2019-2020, Mumbai Suburban has lost considerable mangrove footprint and is set to lose more.
With its current rate of mangrove loss, Mumbai is set to embrace a similar fate as Chennai during the recent flood events. In 2005, when Mumbai was swept with devastating floods, the suburban sector of Lokhandwala was spared nearly Rs. 500 crores in property loss due to its maintained mangrove cover, according to a media report. With soaring land prices, even minor flooding can have drastic monetary repercussions for the city, making Mumbai’s mangrove cover even more important in In Chennai, where large swaths of wetlands and agricultural lands have been developed and increased concrete cover has reduced infiltration of rainwater and increased surface runoff, the recent flood event debilitated this metropolis, bringing Chennai to a complete halt.
The way forward
India’s metropolises need rooted solutions to combat the impacts of rising tides. Replanting mangroves alone cannot be a solution. Remaining urban mangrove tracts need infallible protection and consistent monitoring to ensure encroachment, illegal logging and waste dumping do not take place. Existing mangroves have high capacity to protect coastlines, as seen in Tamil Nadu’s mangrove stands during the 2004 tsunami or in the Sundarbans during Cyclone Amphan in May 2020. Maintaining stand density and mangrove species’ diversity and not diverting that land to alternate purposes is critical to maintain this ecosystem service.
It is not enough to maintain structural integrity by planting an equal number of mangrove saplings that were cut; to maintain functional integrity, the role of mangroves in the larger ecology of the intertidal zone must be understood and retained.
According to Yuvan Aves, a naturalist and nature educator, we need to start viewing mangroves not as trees but as entire ecosystems. From the shifting tides to the tiny crabs that scuttle along the tangled roots of these forests, to the shorebirds pecking on the exposed seafloor before the tide washes in, mangrove forests are living, thriving ecosystems where every species contributes towards the productivity and ecosystem services that we attribute to mangroves.
Forests of land and sea, mangroves are key players in safeguarding India’s coastal cities. By investing more in researching the ecosystem services of mangroves and quantifying them as economic values, and by involving citizens in their conservation and restoration, we can reduce the impacts of coastal storms and sea level rise on India’s vulnerable coastal megacities and the people who call them home.
Banner image: Mangroves in Udupi. There are more than 70 species of mangroves and different species have varying tolerances towards salinity. Photo by Sudeshna Gupta.