Mangrove forests are one of the most vital and fascinating ecosystems on the planet. They occur worldwide in areas with low-oxygen soil, where slow-moving water allows fine sediments to accumulate; because they adapt to the low–oxygen condition of water logged mud. Mangrove forests grow worldwide in the tropic and subtropics, and even some temperate coastal areas mainly between latitude 300 North and 300 South with the greatest mangrove areas within 50 of the equator. They are actually hardy shrubs and trees growing in harsh coastal conditions at the boundary between the land and the ocean.
They can’t withstand freezing temperatures and occupy merely 0.5 per cent of the world’s tropical and sub-tropical coastal areas. But they are often called the ‘unsung heroes’ of the ocean due to their numerous benefits and crucial roles they play in maintaining the health of marine ecosystems. . The word ‘mangrove’ comes from the Guarani word mangal which means ‘crooked tree.’ The plural of mangrove ~ mangroves ~ refers to the population or community composed of several individual mangroves of the same species or different species. Historically, mangrove plant families first appeared during the late Cretaceous to Palaeocene epochs, and became widely distributed in different parts due to movement of tectonic plates.
The oldest knowe fossil of mangrove palms dates back to 74 million years ago. While most plants have roots that are entirely underground, mangroves have roots that are partially above ground, called aerial roots which serve as ‘snorkels’ for breathing when soil is flooded or has little oxygen. They are called halophytes which means they do not require salt water to live but are able to tolerate it.
They do so, thereby out-competing freshwater plants, by the processes of micro filtration and salt excretion. Their intricate root systems are covered with tiny pores that filter out salt from the water that surrounds them. At the same time, any of the salt that finds its way into the plants is excreted through salt glands located on the base of mangroves leaves. These processes work so well that a thirsty traveler could cut the root of a mangrove and obtain fresh drinkable water.
Mangroves are coastal forests that play a vital role in the functioning of natural environment and for humans. They provide a wide range of ecosystem services through:
* Protecting shorelines from erosions and storms by reducing the height and energy of wind and swell waves passing through them. Loss of energy varies from 13 to 66 per cent over 100 meters of mangroves. Moreover, waves lose their ability to scour the sea bed and carry away sediments. Winds across the surface of water get reduced and propagation or reformation of waves is also prevented. Many mangroves have stilt roots, which are aerial and act as ancho – ring structures to withstand wave action. Dr. Jane Lubchenco aptly said: “Mangroves are the guardians of the coast, protecting us from storms, erosion, and sea level rise.” Pp
* Acting as land builders. Mangroves are considered ‘land builders’. All coast line waves and currents create change, sometimes bringing sediments to the coasts, but sometime causing erosion and the loss of lands. As mangrove vegetation reduces wave energy and slows the flow of water over the soil surface, it reduces the water’s capacity to dislodge the sediments and carry them out of the mangroves area. At the same time the slower water flows can allow increased deposition of sediments. The tangles of slit roots also help the sedimentation of the particulate matter. Networks of mangroves roots provide firm anchorage to the banks of tidal rivers, creeks and also the coast line. Moreover, it is believed that the roots of the mangroves secrete a substance which modifies the coarse particles into fine ones and helps in soil formation.
* Filtering nutrients and pollutants. Mangroves’ dense root systems help to filter nutrients and pollutants efficiently from water. This improves the water quality and benefits both human and marine life.
* Storing carbons. Mangroves make a critical contribution to climate change regulation by acting as one of the top three carbon-capturing ecosystems on Earth, sequencing many times more CO2 than the most comparable biomes, including sea-grass meadows and dry jungles. What’s more, degraded and destroyed mangroves can be regenerated and restored to full capacity in a markedly short period of time. Various processes are at work simultaneously:
(a) Mangrove trees extract CO2 from the air and use it to produce oxygen and carbon through photosynthesis. Thus they convert CO2 into biomass: leaves, branches, wood and roots. When the leaves fall, crabs drag them into their burrow. Indeed, they remove CO2 from the atmosphere about four times more efficiently than other plants.
(b) Water from rivers and the ocean also carries organic materials into forests. The mangroves roots slow down the water, so more of the carbon-rich materials are left behind which settle to the bottom and are covered by finegrained sediments. As those materials remain under water and contain almost no oxygen, the decay processes would slow down release of CO2. As a result, mangrove sediment can store organic carbon for long periods. Scientists estimate that the sediments under mangroves contain an average of three to five times as much carbon as the soils in tropical rain forests. T
he total amount of carbon thought to lie under coastal forests worldwide is bet – ween 4 and 20 billion tons. Depending on the environmental conditions, these carbon sinks grow quickly in some forests and slowly in others.
* Creating Habitat. Mangroves are important to many local coastal species, both terrestrial and aquatic. For many organisms, mangrove forests serve as the starting place for their food web. Detritus (fallen leaves and organic material) serves as a nutrient source for planktonic and epiphytic algal food web. These microorganisms and macro invertebrates then supply the remaining members of the food web with tremendous amounts of nutrients and energy. Mangroves are the breeding and nursery grounds for a number of marine organisms including commercially important shrimps, crabs and fish species.
They also stop contaminants like excess amounts of nitrogen and phosphorous, petroleum products and halogenated compounds from polluting the ocean waters through a process called rhizofiltration, a type of phytoremediation that uses plant roots to remove pollutants from water. Mangrove forests serve as vital habitats for a diverse array of aquatic species, offering a unique ecosystem that supports the intricate interplay of marine life and terrestrial vegetation.
The areas occupied by mangrove ecosystems are being threatened and getting, as a result, smaller and smaller. Apart from the nature’s fury, land-degrading anthropogenic activity is one of the prime factors for destruction of mangroves. In the forest-society interface, unplanned overexploitation of natural resources is very common. Factors included:
(1) draining of forests to gain land for construction;
(2) conversion to aquaculture ponds, rice fields, and soy or palm oil plantations;
(3) contamination from indiscriminate uses of aquaculture chemicals;
(4) pollution from trash and fossil fuel extraction, and
(5) logging for construction materials and fuels. Beginning in 2010, remote sensing technologies and global data have been used to assess areas, conditions and deforestation rates of mangroves around the world. According to one estimate, global annual deforestation rate has been estimated as 0.16 per cent and per country rates as high as 0.7 per cent. We should bear in mind that the loss of mangroves is not just an environment tragedy, but a humanitarian crisis.
The Sundarbans mangrove forests, which span across India and Bangladesh, are the largest of their kind worldwide. The Indian part of the forest is estimated to be about 4,260 square kilometres (40 per cent of the total areas), and it is home to a diverse range of flora and fauna, including 453 wildlife. However, the forest is facing threats such as increased salinity due to sea level rise, reduced freshwater supply and human-made causes like the proposed coal fired power station. To save the Sundarbans, we need to leave it alone. Only thing we can do is to minimize human intervention. The Sundarbans is not a just a matter of development.
It is the matter of conservation of man and beast; of vegetation and the unique world in which each component contributes to the overall ecological balance, and to natural regeneration. Nature in the Sundarbans commands and demands far more respect so that there is neither a ruthless dispossession of the rights of the indigenous people of the region, nor a blatant violation of its environment.
Success of mangrove restoration inexorably depends on fruitful engagement of local stakeholders and on careful assessment to ensure that growing condition will be suitable for the species chosen. For generating awareness the International Day for the conservation of mangrove ecosystem is celebrated every year on 26 July. The importance of mangroves is also recognised by Sustainable Development Goal (SDG) 14, which aims to govern oceans and coastal sustainably. In the words of Dr. Mark Spalding: “Mangroves are not just trees, they are a way of life for millions of people around the world.”
(The writer is a retired IAS officer)