Status, Threats and Conservation of the Wetland Ecosystem Dominated with Mangroves in India

CrossRef, Google Scholar, Scientific Indexing Services (SIS), Scientific Journal Impact Factor (SJIF), CiteFactor, Index Copernicus International (ICI), Directory of Research Journal Indexing (DRJI), General Impact Factor, Journal Factor, Cosmos Impact Factor, PKP Index, AJIFACTOR Indexing, etc. Mangroves are one of the most undermined biological systems. They have immense ecological and economic advantages. Consistent, increment in natural and coastal development like a change of wetlands for hydroponics, construction for tourism, the tsunami has led to the demolishment of mangrove environments in India. The inhabitants of minor zones are at risk of losing their livelihood and there is a threat to the existence of the mangrove ecosystem. It has been noted that from a decade ago, about 40% of the Indian mangrove territories have been lost. At present, the environmental changes and increased anthropogenic activities have become a significant concern for the conservation and sustaining of the mangroves. Conservation of mangrove environment can be accomplished by increasing awareness about their significance among various stakeholders and safeguarding them through mandatory national policy and regulations. A specific policy like Coastal Zone Regulation has been formulated to ensure mangrove conservation, sustainable existence of local community habitat along the coastal area, fishing community, and coastal stretches for marine habitat have been protected.


INTRODUCTION
The total global Mangrove cover spread across 123 countries is about 15 million ha, which accounts for about 1% of the World's Tropical Forest (India State of Forest Report 2019). As per Chapman (1976), mangroves are confined to tropical climates having an average monthly minimum air temperature of 20°C and above (Ellison, 1999). About 110 mangrove species belonging to 20 families are identified globally (Myint et al. 2019). In 1913, the term 'mangrove and 'mangrove' has been noted by the oxford dictionary, representing tropical shrubs or trees which are present in coastal swamps along with their tangled roots, which grow above the ground level (Mepham, 1985). According to one classification mangrove species are classified into two categories namely i) exclusive species (strict/obligate/true mangrove), they are found confined to mangrove environment only and ii) non-exclusive species (semi/back mangrove or mangrove associate), they are found in the mangrove, aquatic and terrestrial environment (Wang, 2011). The species of genus Rhizophora are exclusively found in mangrove forests and are not found in terrestrial networks. Mangroves, for the most part forming unadulterated stands, assume a critical role within the structure of the network. A morphological specialization in the mangrove environment is a salt blocking mechanism. Distinctive notable strengths of mangrove plants include airborne roots to check for anaerobic deposits, tie-rod-like support structures and roots that provoke outer soil, low tide potential, and high energy potential, salt fixation, salt discharge sliding viviparous leaves and shoots (Duke et al. 1998). Mangroves are a biological group of halophytic plants which are well known for salt tolerance. They are important biomass that protects the juvenile stock. Mangroves are valuable coastal habitats heavily loaded with nutrients which they constantly share with the adjacent habitats. They provide a large variety of economic as well as ecological products and support the diversity of marine and coastal ecosystems (Singh et al. 2012). Mangrove ecosystem has endangered as well as endemic species and is considered as the world's richest storehouse of ecological and economical values (Sandilyan, 2014).

Economic Benefit
Mangroves provide a benefit of more than US$ 65 billion/year in terms of flood protection (Menéndez et al. 2020). They act as a defense for the coastal wetlands and protect estuaries from cyclonic storms as well as battering waves (Ellison, 2008). If protection of human lives is considered, Vietnam, India, and Bangladesh receive maximum benefit but in terms of economic benefit, the USA, China, India, and Mexico receive the maximum benefit. Further, developing nations having mangrove vegetation receive a benefit of about US$ 33,000-57,000/ha/year (Menéndez et al. 2020). Costanza et al. (2014) estimated that the mangroves and tidal marsh provided about US$ 194,000/ha/yr worth of ecosystem services in 2011 which included benefits from storm protection, erosion prevention, etc. (http://www.mangrovealliance.org). Mangroves help people living in their vicinity by providing food, fuel, wood, pulp, etc., some of which are harvested commercially for livelihood. A diverse life form breed in the mangrove environment, including fishes, crabs, shrimps, mollusks, and warm-blooded animals like ocean turtles. They are home to a variety of settling, reproducing, and transitory winged animals.

Carbon Sequestration, Sink and Storage
Two huge repositories: The earthbound biosphere and the sea take up CO2 roughly to an equivalent extent. A more prominent coefficient of difference for the take-up via land and sea demonstrates extensive yearly inconstancy in the assessment of CO2 stockpiling by the sea and land. This could be because of the debilitating sink quality of the sea and expanding the limit of woods take-up in reaction to air CO2 increment (Costanza et al. 2014;Spiecker, 1996). About 62-78% of the worldwide earthbound C is sequestered in the woods, and about 70% of this C is put away in the dirt with a moderate turnover rate (Lewis, 2004;Ciais P, 2008). Mangrove woods represents about 2.4% of tropical woods (Schimel, 1995) and to improve the precision of worldwide carbon sink evaluation of carbon elements is basic in the mangrove swamps (Guggenberg, 1994). Of the global forest cover, mangroves are responsible for only 1% of the carbon sequestration, but as a coastal habitat, the carbon sequestration is as high as 14% (Spalding, 1997). Globally, it is estimated that mangroves store about 21,914.17 Mt CO2 of total organic carbon. Of this, 19,093.67 Mt CO2 is stored in the upper 1 m of soil, and the remaining 2,820.50 Mt CO2 in the above-ground biomass (Chmura, 2003).

Biodiversity
Mangrove biological system is substantial in inherited variety because of the event of both oceanic and earthbound species and their flexibility to a wide scope of harsh natural conditions, for example, high saltiness, high temperature, sloppy anaerobic soils, outrageous tides, and solid breezes, which changes viciously and now and again (Alongi, 2012). By and large, the biodiversity of mangroves environments can be extensively classified into two gatherings for example select / significant mangrove species (additionally called exacting / commit/ genuine mangrove) and non-elite / minor / partners mangrove species (www.globalmangrovewatch.org ). The significant species are the severe or genuine mangroves. The minor mangrove species are less prominent components of the vegetation and infrequently structure unadulterated stands generally includes diverse endophytes. Das et al. (2014), reported about 74 mangrove species belonging to 27 genera from 20 families scattered through the world. Mangrove-related microorganisms incorporate microbes, growths, and organisms like protists, macroalgae, seagrasses, saltmarsh (Spartina), and different verdures, for example, various epiphytes (Vannucci, 2000;Tomlinson, 1986). In the tropical mangrove woods, there are roughly 100 epiphytic species from the families Orchidaceae, Bromeliaceae, Cactaceae, Araceae, Piperaceae, and Polypodiaceae dispersed through the covering and on trunks of mangrove trees. Mangrove-related faunal species are zooplankton, wipes, ascidians, epibenthos, infauna, meiofauna, prawns, shrimp, crabs, creepy crawlies, mollusks, fish, creatures of land and water, reptiles, fowls, and vertebrates (Das, 2014).

Aquaculture
In particular, the carrying capacity of the biological mangrove forest system for sea-going biota is obtained by the release of nutrients from mangrove leaf litter that tumbles to the lower part of the waters and assumes a substantial proportion as a supplementary turnover supply (N and P) that eventually influences the stock of fish. Fishermen look for fish, shrimp, and another water biota. Khalil, A. S. (2015) observed that the successful shrimp fisheries in Pakistan depend entirely on mangrove ecosystems.

Medicinal value
The secondary metabolites of A. officinalis like diethyl phthalate, hydroxy-4-methoxy benzoic, and oleic acid obtained from the leaves exhibited antibacterial and anticancer activity (Kathiresan, 2010;Giri, 2011). Spiro benzofuran, a flavonoid present in the leaf concentrates of A. corniculatum has antiplasmodial activity against Plasmodium falciparum (Khalil, 2015). The naphthoquinone namely 1,4-furanonaphthoquinone and its analogs from Avicennia plants displayed anticancer activity (Bhimba et al. 2010). Luteolin, from A. It has been found that marinas have antiproliferative and apoptosis functions. Undesirable concentrate of tea mangroves collected from the product of mangrove plants. Due to procyanidin present in the concentrate, R. Stylosa had high cell growth (Sundaram, 2012). Benzamide, an isolated alkaloid from Rhizophora. Antifouling behavior against barnacles was seen in mucronate. Benzamide, an alkaloid isolated from R. mucronata, antifouling activity toward barnacles was detected Cyclotella caspia (Itoigawa, 2001). Paracaseolide A with anticancer activity was isolated from the Sonneratia paracaseolaris mangrove plants (Miranti, 2018). Alkaloids present in the mangrove plant A. ilicifolius L. demonstrated to have activity against hepatic fibrosis in rodents (Liu, 2013). Procyanidins of Heritiera fomes were shown to have antimicrobial activity (Chen, 2011). Two tannins have been isolated from mangrove Kandelia candle and R. mangle and assessed for their antioxidant potential by Zhang et al (2010) and Wai et al. (2015).

INDIAN MANGROVES
India has a coastline of about 7516.6 km. Longitudinally mangroves habitats are present between 69°-89. Biannual monitoring of mangroves started in India in 1997 through remote sensing techniques. Table 1 gives the statewise distribution of mangrove areas in the different states/union territories of India from 1987 to 2019. The mangrove vegetation was detected in only 7 states/union territories in 1987 but its presence increased to 12 states/union territories in 2019. A recent survey done in 2019 showed that an area of 4,975 km² has been covered by mangrove which is about 3% of total mangrove cover in South Asia. Out of the total area, West Bengal has maximum mangrove cover (2112 km 2 , 42.45%) followed by Gujarat (1177 km 2 , 23.66%) (Fig. 1). Overall, mangrove cover has increased by 929 km 2 from 1987 to 2019, where the highest growth is seen in Gujarat which is about 750 km 2 followed by 180 km 2 in Maharashtra, 52 km 2 in Odisha, 36 km 2 in West Bengal, and 22 km 2 in Odisha. A decrease in mangrove cover is seen in Andhra Pradesh (91 km 2 ) and Andaman and Nicobar (70 km

MANGROVE DIVERSITY
India has rich species diversity with a total of about 4,011 species. Of this, 77% is fauna (3091 species) and 23% flora (920 species). Out of the flora, the highest diversity of marine algae was around 60%, followed by fungi (11.2%), bacteria (7.5%) mangrove associates (9.3%), and mangroves (7.5%). (4.2%). There were approximately 59 species of mangroves in India from 41 genera and 29 families. On the east coast, almost 25 mangrove species have restricted distribution. It supports the lower organisms like planktons and benthos to dwell in the mangrove ecosystem. In India, 105 species of pieces are found which are supported by mangroves (Iftekhar, 2008).

Threats to Mangrove
Climate change has become a great concern for hydrological and ecological habitats and it is investigated by worldwide researchers. Due to its possible impacts on the increase in air and water temperature, the coastal region due to sealevel rise, the increase in atmospheric CO2, changes in the quantity and nature of continental runoff, changes in the frequency and severity of extreme weather events, it is critical, etc. The different climatic conditions are extensively harmful to most of the wetland ecosystem (eg. Plankton, Benthic animals) (Goutham et al. 2014;Wakle, 2018). Mangroves usually respond to hazards which are resulting from global climate change because of the location at the continent-ocean interface Coastal wetlands have the potential to adapt to the rising waters and changes in local storm patterns under natural circumstances, but unfortunately, the combination of climate changes and human activity jointly alters natural conditions and disrupts coastal wetland hydrology, biogeochemical cycling and other processes (McLaughlin, 2002). Constant changes in an ecosystem lead to the tsunami which happened during the year 2004 in the Andaman and Nicobar also agricultural area affected in Andhra Pradesh along with other developmental activities of all the treats to mangrove, rise in ocean level might be the most dangerous (Durant, 2004;Morris, 2002), but even then, it is still a modest danger compared to anthropogenic activities like hydroponics cultivation (Field, 1995;Lovelock, 2007;IUCN,1989;Primavera, 1997). Rise in ocean level may be a significant reason behind anticipated decreases in the zone and wellbeing of mangroves and other flowing wetlands in the future (Alongi, 2002;Duke, 2007;Ellison, 1991;Nichols, 1999;Ellison, 2000;Cahoon, 2006, www.wpcouncil.org ). Some of the major threats affecting the mangrove ecosystem are presented in Table 2.

Coastal Regulation Zone (CRZ)
Random development had begun along the coasts, especially the sandy stretches of the nation, as there were not very much characterized laws administering beach front exercises. A remarkable enactment, called the Coastal Zone Regulation (CRZ) Notification (MoEF, 1991), issued under the Environment Conservation Act of 1986, was authorized by the Ministry of Environment and Forests. The principal motivation behind this notice was to secure, control, and limit ecological harm to delicate seaside stretches and biological systems including estuaries and backwaters from spontaneous human impedance, The government declared coastal stretches of oceans, bayous, estuaries, lakes, wetlands, and backwaters that are impaired by flowing movement (on the land side) up to 500 meters from the High Tide Line (HTL) and the Coastal Control Zone (CRZ) land between Low Tide Line (LTL) and HTL, as well as forced limits and proposed regulations for various beach front exercises.
The warning records different precluded exercises, a guideline of admissible exercises, techniques for checking and requirement, waterfront region characterization and improvement guidelines, standards for guideline of exercises, and definite rules for the advancement of seashore resorts and other residences. Table 3 highlights the differences between CRZ 2011 and CRZ 2018. Coastal zone regulation brings into existence for the security of local community habitat besides coastal area, fishing community and for the preservation of coastal stretches for development of marine environment to control the sea level rise because of global warming. As per CRZ 2018, 500 m is a range for the land area from the high tide line along the seafront. On the landward side, 500 m is the land area in between of high tidal line and hazard line.
The State Forest Departments and the Ministry of Environment and Forests, the region under the mangrove biome is growing, Government of India by way of forestation, restoration, plantation and conservation of mangroves. There is also a need for greater awareness through education to the masses and to make the forest guard and people living in the vicinity of mangrove ecosystems aware of the loss due to mangrove degradation.

CONCLUSION
The mangrove species have extraordinary significance in terms of the global economy and environment and hence need to be preserved as increased anthropogenic activities and natural calamities have led to a significant loss of mangrove forest area. Anthropogenic activities like oil spills, cutting of mangroves, aquaculture, agricultural expansion, tourism are major threats to the survival of mangroves. Besides, environmental changes like rising CO2, ocean level and temperature, environmental pollution, cyclones, etc have added to the destruction of the mangroves. Intense global research and mangrove status assessment has led to national-level policy formulation and increased awareness drive among various stakeholders and the people dependent on and living in the vicinity of mangroves. Due to this, a gradual increase in area under mangrove vegetation is observed. There is a need for greater awareness as well as conservation and plantation efforts are required for the sustaining of the mangroves.