Mangrove ecosystem – mangroves form dense and often mono-specific strands and are considered “foundation species” that control population and ecosystem dynamics. Currently declining at the rate of 1 per cent per year, mangrove forests are expected to completely disappear within 100 years if nothing is done to remedy it.
The Mangrove Ecosystem of India
Mangroves are uniquely adapted to tropical and subtropical coasts, and although relatively low in number of species, these forests provide numerous ecosystem services and support coastal livelihoods worldwide. They are the only tall forests on the earth where land, freshwater and saltwater mix. Many mangrove forests can be recognized by their dense tangle of prop roots that make the trees appear to be standing on stilts above the water. Mangroves are one among the most productive ecosystems on the earth. The roots slow the movement of tidal waters, causing sediments to settle out of the water and build up the muddy bottom. They are also known as tidal forests or coastal woodlands. The intricate root system of mangroves makes these forests attractive to fish and other organisms seeking food and shelter from predators. The definition of a mangrove species is based on a number of anatomical and physiological adaptations to saline, hypoxic soils. These include viviparous or cryptovlviparous seeds adapted to hydrochory; pneumatophores or aerial roots that allow oxygenation of roots in hypoxic soils; and salt exclusion or salt excretion to cope with high salt concentrations. The species that are exclusively restricted to tropical intertidal habitats have been defined as ‘true mangrove’ while those are not exclusive to this habitat have been termed ‘mangrove associates’.
Mangrove Ecosystem – GLOBAL DISTRIBUTION
Mangroves occupy less than 1 per cent of the world’s surface and are mainly found between the Tropic of Cancer and the Tropic of Capricorn on all continents covering an estimated 75 per cent of the tropical coastline worldwide within 123 countries. Due to presence of harsh environmental adaptation during high salinity, high temperature, extreme tides, high sedimentation and muddy anaerobic soils, they are able to cover a total of 152362 sq. km. areas of the world with the contribution of 22402 sq. km. of North and Central America, 23883 sq. km. of South America, 51049 sq. km. of Southeast Asia, 624 sq. km. of Middle East, 215 sq. km. of East Asia, 5717 sq. km. of Pacific Ocean, 7917 sq. km. of East and South Africa, 10171 sq. km. of Australia and New Zealand, 10344 sq. km. of South Asia, and 20040 sq. km. of West and Central Africa.
Indian mangrove cover is distributed with a total area of 4627.63 sq. km. among 12 maritime states and union territories. West Bengal harbors 45.31 per cent mangrove cover while 1 sq. km. of mangrove cover is recorded from Puducherry.
A total of 70 species of true mangroves are recorded across the globe while India represents a total of 125 species including 39 species of true mangroves and 86 species of associates. The highest species diversity is recorded from Odisha with a total of 101 species while Gujarat harbours 40 species. Three types of mangrove formation can be seen such as deltaic, backwater-estuarine and insular. The deltaic mangroves occur mainly along the east coast, the backwater-estuarine type along the west coast and the insular type in the Andaman and Nicobar Islands.
The services of the mangrove ecosystem are essential for the sustainable development of biodiversity as well as coastal protection, fishery resources. etc. and estimated economic value is 2,000-9,000 USD per ha per year. The detailed services are depicted below.
Coastal Protection: They protect inland human communities from damage caused by coastal erosion and storms. In areas where mangroves have been cleared, coastal damage from hurricanes and typhoons is much more severe.
Preventing soil erosion and siltation: The dense root systems of mangrove forests trap sediment flowing down rivers and off land. They stabilize the coastline and preventing erosion from waves and storms. By filtering out sediments, the forests also protect coral reefs and seagrass meadows from being smothered in sediment.
Ecosystem Services: Mangroves form dense and often mono-specific strands and are considered “foundation species” that control population and ecosystem dynamics, including fluxes of energy and nutrients, hydrology, food webs, and biodiversity. Mangroves have been widely recognized as supporting numerous ecosystem services including flood protection, nutrient and organic matter processing.
Habitat and Nursery: Mangroves provide a critical habitat for a variety of terrestrial, estuarine and marine species, and serve as both a source and a sink for nutrients and sediments.
Timber and Plant Products: Mangrove wood is resistant to rot and insects. The mangroves are also being commercially harvested for pulp, wood chip and charcoal production. Tannin, a compound known for its ability to bind with certain types of proteins to form a strong, flexible, resistant insoluble substance known as feather is extracted from the bark of some mangrove species. In many coastal areas including the Gulf of Kutch, the mangroves area substitute for fodder thereby reducing pressure from the scarce pasture lands. Mangrove based tourism is a nascent concept in India and initiated as ecotourism for the recreational purpose of tourists.
Therapeutic uses of mangroves: Mangroves are widely used in the treatment of malaria, diarrhoea, snake bites, ulcers, diabetes and skin infections.
Mangroves habitat serve as one of the best nursery grounds for the development and aggregation of several fauna species. A total of 3111 species of mangrove associated fauna are recorded in India.
It is estimated that 26 per cent of mangrove ecosystem of the world are degraded due to over-exploitation for firewood and timber production. Similarly, clearing of mangroves for shrimp culture contributes to 38 per cent of global mangrove loss, and with other aquaculture it is around 14 per cent.
In India, over 40 per cent of mangrove area on the western coast was converted to agricultural fields and converted to urban areas. The global loss is sporadic, and only around 20 to 35 per cent of mangrove area has been reported since 1980. The rate of mangrove decline is approximately 1 per cent per year. The current exploitation rates are expected to continue unless mangrove forests are protected as a valuable resource. Given their accelerating rate of loss, mangrove forests may at least functionally disappear in as little as 100 years.
The identification and implementation of conservation priorities for mangroves on the basis of comprehensive species-specific information is required to safeguard this vulnerable ecosystem. Designation of critical habitat, no take zones, or marine protected areas are the initial steps along with the protection of species specific habitat, management of anthropogenic pressure, establishment of green belt and buffer zone, restoration of degraded species, and mapping of mangrove cover to conserve the mangrove in a sustainable manner.
Source: Director, Zoological Survey of India, Kolkata, 2017.