Effects Of Mangrove Destruction In Mumbai Environmental Sciences Essay
Rapid expansion of urban spaces has caused pressure on fragile ecosystem of the city. Uneven growth of various regions has made migration a serious challenge. Increasing population growth of metropolitan has created concretization of island city and clearing of vital floral resources.
Thousands of people from various parts of the country come to Mumbai every month. Around 43 per cent of city’s population considered to be migrant. The predominant migrants are of rural origin, coming from various parts of the country, with two-third to three-fourths of all migrants belonging to this category. There are migrants from other countries as well but these have been less than one per cent since 1981 (Census; 2001). This trend migration is a Destruction of mangrove that was the habitat of several species of fishes have combined to leave the city’s fisher folk of around 50,075 (Marine Fisheries Census; 2005) gasping for survival. Among various reasons economic factors have been the major cause for migration to Mumbai. About 69 per cent of males stated that employment was the main motive behind their movement. The data show that the rate of migrants in search for better employment has been higher in the late 1990s. Social reasons such as marriage and accompanying the family constituted about 90 per cent of female migration. (Singh 2001)
Population pressure is continuously increasing in the coastal area, so because of this expanding population mangrove is facing significant pressure of destruction. Mangroves have been cleared and degraded on an alarming scale during the past four decades (Valiela et al., 2001; Wilkie and Fortuna, 2003; Duke et al., 2007), yet they remain an important source of wood and food products and provide vitally important environmental services for coastal communities throughout the tropics (Balmford et al., 2002).
Climate and Rainfall
Kolis of Mumbai
Kolis are the traditional fishing community of Mumbai and are the original inhabitants of the island city. Fishing is still the main source of their livelihood. The interesting fact is that, Mumbai is derived from the Koli word, ‘Mumba’, which means goddess of water. Several records reveal that Kolis have been found in Mumbai from early times. Dr. Gerson da Cunha in the book ‘Origin of Mumbai’ describes old Mumbai as ‘the desolate islet of the Mumbai Koli fishermen. The Kolis are reported to have occupied the land in A.D. 1138 The Koli community has several subcastes, the prominent ones are Koli kolis, Mangela Kolis, Mahadeo kolis, Suryawanshi kolis, Vaity kolis, Koli Christians. Kolis are divided into two occupational classes;
Dolkars are usually rich compared to Vatsad among Kolis. Dolkars practice fishing on large scale Vatsads, who are a poor class of fishermen usually in the employ of the richer members of the community. Men are mostly engaged in fishing while, women take care of housing activities and selling of fish in the local market. Lot of their daily activities depend on the fishing season and tidal movement. Koli is the main language spoken by the community, Marathi is another frequently used language among Kolis.
What are Mangroves?
Mangroves are a group of trees, palms, shrubs, vines and ferns that share a common ability to live in waterlogged saline soil. These plants have developed unusual adaptations to the unique environmental conditions in which they are found. Mangrove can be typically refered to an individual species. Terms such as mangrove ecosystem, mangrove forest, mangrove community and mangrove swamp are used interchangeably to describe the entire mangrove community (Smithsonian Inst. 1996). There are around 80 species of mangroves found throughout the world (Saenger et al., 1983). Mostly they occur within tropical and subtropical coastal areas subjected to tidal impact. Tidal area can be interpreted to mean a shoreline inundated by the extremes of tides, or it can more widely refer to river-bank communities where tides cause some fluctuation in water level but no change in salinity (Tomlinson, 1986).
There are mainly two types of mangrove; exclusive and non-exclusive. Exclusive mangroves are the largest group, comprising around 60 species (Saenger et al., 1983). These mangroves are confined to intertidal areas. Rest 20 species are referred as non-exclusive. Non-exclusive mangroves differ from the exclusive mangrove in the sense that these grow preferably in drier and more terrestrial areas.
Features of Mangrove
Mangrove forests comprise up to 50 species of woody halophytes restricted to sheltered saline tidal areas, and once occupied around 75% of tropical coasts and inlets (Ellison 1997). Mangroves are the plats of tropical sheltered shores. Mangroves are found throughout the world between latitudes 32°N and 38°S. The upper and lower limits of this range are determined by temperature (Chapman, 1976; Tomlinson, 1986).
(Source: ENVIS, 2008)
Mangrove Distribution in India
According to the Government of India, the total area of the mangroves in India was around at 6,740 sq. Km. this covered about 7% of the world mangroves (Krishnamurthy, 1987) and about 8% of the Indian coastline (Untawale, 1987). But recent 2005 data of Survey of India, Dehradun shows an extent of 4,445 sq. km. mangrove areas in India. Out of the total acreage, 57% of the mangroves are found on the East Coast, 23% on the west coast and the remaining 20% on Andaman and Nicobar Islands.
Table: State/UT wise Mangrove Cover Mangrove Cover Assessment 2001(Area in sq. km.)
% of Geographical Area
Andaman and Nicobar
(Source: ENVIS, 2008)
Mangrove Distribution in Maharashtra
Maharashtra has 720 km long coastline, which has various characteristic features of beaches and rocky cliffs flanked by estuaries and patches of mangroves. Maharashtra coastal zone extends between the latitude 15 52'N and 20 10'N and longitude 72 10'E and 73 10'E and falls under five districts of Thane, Mumbai, Sindhudurg, Raigad, Ratnagiri. The mangroves of Maharashtra are the most diverse among the west coast and according to the Forest Survey of India (FSI) covered 116 sq. km in 2003. The area under mangroves in Maharashtra was 200 sq. km. in 1972-75, which reduced to 108 sq. km. in 1997.
Mangroves of Mumbai
Mangrove along the coast of Mumbai always faced the challenge of various anthropogenic activities over the decade. In early nineties around 37 sq.km. Of mangrove existed in Mumbai, mostly in Versova, Gorai, Mahim creek, Thane and Ghodbunder. Some sparsely covered patches of mangrove are also found in Bandra, Colaba, Mahul and Malabar Hill.
The most commonly occurring species of mangrove in Mumbai is Avicennia marina, this covers the almost 60 per cent of species diversity. The characteristic feature of Avicennia marina makes it tolerable for high salinity area. This species also tolerates pollution including heavy metals such as lead, mercury and chromium.
Table: Some of the commonly found mangroves in Mumbai
(Source: Kulkarni, 2007)
Mangroves mostly occur in areas where the average temperature of the coldest month is higher than 20°C and the seasonal range does not exceed 10°C. Lower temperature and frost also limits the growth and distribution of mangrove (Tomlinson, 1986).
Coastal areas which receive ample amount of rainfall, heavy runoff and seepage into the intertidal zone from the hinterland are most suitable for mangrove. These areas receive extensive sedimentation which provides huge quantity of nutrients, which in turn are favourable for mangrove growth (Tomlinson, 1986).
Importance of Mangrove
Multifaceted importance of mangrove has been realised in recent times but its ecological importance is known to scientific community since hundreds of years. Importance of mangrove can be broadly classified under following heads:
Mangroves are considered to be the most productive natural ecosystem throughout the world. Mangrove ecosystem comprise of numerous varieties of flora and fauna. Mangrove forest consist of seventy taxonomically diverse tree, shrub, palm and fern species under twenty-seven genera, twenty families, and nine orders that share a suite of convergent adaptations to saline, anoxic habitats (e.g. Tomlinson, 1986; Stewart & Popp, 1987; Ball, 1988; Duke et al, 1998).
Mangroves provide a vast range of wood and non-wood forest products which are of good economic value such as timber, fuel wood, medicine, thatch, honey, fodder, charcoal etc.
Legislative Framework for Conservation and Management of Mangrove in India
The Indian Forest Act, 1927: Provide protection to “flora and fauna”. The Indian Forest Act has been applied to the mangrove forest of the Sundarbans, which have been declared as a “Reserved Area”.
The Wildlife (Protection) Act, 1972: Provide protection to “flora and fauna”. Although they do not specifically mention mangroves, these acts can also apply to the conservation of the flora and fauna of mangrove ecosystem.
The Forest Conservation Act, 1980: States that “No forest area shall be diverted for any non-forestry purpose” without prior approval of the Government of India. This act has proved very effective in preventing diversion of mangrove forest area for non-forestry purpose.
Coast Guard Act, 1978: The concern for “Marine and Coastal waters” has led to formation of a special force, The act stipulate that Cost guard should combat oil pollution beyond 5 km in the sea and perform surveillance duty against international dumping of oil or waste by ship/tanker.
The Environmental (Protection) Act, 1986: It has a crucial role in the Conservation and Management of mangrove ecosystem. It declares a “Coastal Regulation Zone” notified in 1991, in which industrial and other activities such as discharge of untreated water and effluents, dumping of waste and land reclamation are restricted in order to protect the Coastal environment.
Condition of Mangrove in Coastal Regulation Zone
It is stipulated that in case of mangrove with an area of 1000 sq.m or more, would be classified as CRZ with a buffer zone of at least 50 m Mangrove is a tropical tree growing, along the coast and requires saline water for its growth. Expert in this field say that mangrove are very important along the coast for breaking of tides and it is valuable resources having several direct uses. Hence proper the protection of mangrove is very important. (Chauhan, 2004)
Prohibited Activities in the Coastal Regulation Zone
(a) Setting of new industries and expansion of existing industries (except those directly related to waterfront or directly needing for shore facilities).
(b) Manufacture, handling, storage or disposal of hazardous substances.
(c) Setting up and expansion of fish processing units including warehousing
(d) Discharge of untreated wastes and effluents from industries, cities and other human settlements.
(e) Dumping of cities and town wastes for the purpose of land filling.
(f) Dumping of ash or any wastes from thermal power station.
(g) Land reclamation bunding or disturbing the natural course of seawater with similar obstructions except those required for control of coastal erosion.
(h) Mining of sands, rocks and others sub strain materials except other minerals not available outside the CRZ areas.
(i) Construction activities in ecologically sensitive areas.
(j) Any construction activities between the Low Tide line and high tide line except in permitted areas.
(k) Dressing or altering of sand dunes, hills natural features including landscape changes.
Regulation of Permissible Activities in Coastal Regulation Zone
1. Clearance shall be given for any activities within the CRZ if it requires waterfronts and fore shore facilities.
2. The following activities will require environmental clearance from Ministry of Environment and Forest Govt. of India.
a) Construction activities related to defence requirements for which fore shore facilities are required (e.g. Jetties etc.).
b) Operational constructions for ports and harbours and lighthouses requiring water frontage Jetty, waves quays etc.
c) Thermal Power Plants (only foreshore facilities for transport of raw materials for intake of cooling water and out fall for discharge of treated waste water).
d) All other activities with investment exceeding rupees Five Crores.
3. a) The Coastal states and Union territory Administration shall prepare Coastal Zone Management Plans at the earliest and approval be taken from Central Govt. in the Ministry of Forest and Environment.
b) Within the Framework of such approval plans the State Govt./U.T. Administration or local Authorities shall regulate all development and activities within the Coastal Regulation Zone.
Violation of Coastal Regulation Zone has been seen in various parts of Mumbai Metropolitan region. Several environmental activists have raised the voice against these violations.
Coastal area is vital to the prosperity of country and usually most productive areas, supporting a wealth of marine resources. With rapid industrialization, urbanization, resultant pollutions and depleting resources along the coast have resulted in degradation of coastal ecosystem and diminishing the living resources. Environmentally effective coastal zone management requires accurate, up to date and comprehensive scientific data on which policy decision can be used.
Mangrove Destruction and its Impact
Importance of mangrove has been recognised by various stakeholders of the society viz. scientists, government, local populations of biotic and socioeconomic services. Accurate estimates of global deforestation rates of mangroves are not available; its well-known environmental and socioeconomic impacts are observed and increasingly documented in coastal communities that depend directly on mangroves, and in upland communities with economic links to the coast.
The primary cause of destruction throughout the world is clear cutting, illegal dumping and reclamation; these are carried for the purpose of agricultural activities, aquaculture, urban expansion, and resort development and have threatened the majority of mangrove ecosystem. This destruction exacerbating economic stress of largely low-income, fast growing local population, who are driven to exploit mangroves despite clear signs of degradation.
Mangrove forests are a source of livelihood for thousands of coastal communities in developing countries worldwide; these communities traditionally harvest fish, shrimp, timber, non-timber forest Products, and fuel wood from them. The importance of the mangrove ecosystem transcends provisioning services and includes regulatory, ecological, cultural, and aesthetic services. However, these services are diminishing globally, most especially the provisioning service, and this is putting the livelihoods of coastal communities at risk and increasing their vulnerability to tropical storms and surges. These trends are the outcome of mounting anthropogenic activities such as brackish water aquaculture, mangrove forest clearing for infrastructure development and varied levels of harvesting for subsistence.
Because of these pressures, mangroves in coastal tropical developing countries are being degraded; for instance, 20-30% of mangrove forests have been lost in West-Central Africa since 1980 (UNEP-WCMC, 2007).
Mangrove and Fishing
Linkages Between Mangrove and Fishing
Fishes and invertebrates use estuarine and inshore habitats in a number of ways: some are only occasional visitors; some use them only at certain life stages, whereas others reside permanently in the estuaries (Lenanton & Potter 1987, Potter et al. 1990, Potter & Hyndes 1999, Whitfield 1999).
There are various groups of fishes and invertebrates which show distinct association with mangrove. Fishes which are found occasionally in estuaries are termed as marine stragglers (Potter & Hyndes 1999, Whitfield 1999) and these stragglers have least dependence on estuaries.
There are species which uses estuaries and inshore regions for significant time period especially during juvenile stage only. In some marine species juveniles are only found in mangroves and these are termed as mangrove dependent species; e.g., banana prawn P. merguiensis (Staples et al. 1985, Vance et al. 1996). Catadromous species travel between fresh and marine water also use mangrove habitats at certain life stages e.g., barramundi Lates calcarifer (Russell & Garrett 1983). Some species spend their entire life cycle in estuaries and are termed as true estuarine species.
The importance of mangrove for sustaining production of fishery in coastal ecosystem is a widely held paradigm that mangroves act as important nursery sites for fisheries species. The function of mangroves as nursery sites is widely accepted (e.g., Blaber 2000, Kathiresan & Bingham 2001) and this paradigm is used for important management decisions on habitat conservation and restoration of mangrove (Beck et al. 2001). There are also theories that states; area of mangrove habitat in an estuary translates to the secondary production and catch of commercial fisheries (Baran 1999). There are clear cases of example which depict the correlation between the magnitude of commercial finfish catches and the extent of mangroves. For example, in the Philippines, a positive, but weak, correlation was found between mangrove area and the catch of four families of commercial fish (Paw & Chua 1991).
Freshwater Mangrove Marine
Freshwater Mangrove Marine
Figure Number of fish and shrimp species occurring in freshwater, marine and mangrove ecosystem showing higher species diversity in the mangroves (Islam & Haque 2005).
Mangrove as nursery site for fishes:
Mangroves and estuaries share characteristic features such as shallow water, reduced wave action, high organic content in the sediment, high primary production and protection from predators, which may all contribute to their role as nurseries. Nursery areas for fishes have been regarded as any areas inhabited by the juveniles, often with the adults living in separate habitats. But, this definition of nursery is challenged by Beck et al, (2001); he proposes a different picture of fish nurseries “a habitat is a nursery for juveniles of a particular species if its contribution per unit area to the production of individuals that recruit to adult populations is greater, on average, than production from other habitats in which juveniles occur”. According to this definition nursery is that part of habitat area of juvenile which are most productive in terms of supply of recruits to adult populations and, therefore, to fisheries.
Based on the reproductive pattern and its association with the mangrove fishes can be classified into following four categories:
a) Regular spawners
The spawning activity of the species occurs regularly in the mangrove. The species are not necessarily resident in the region, but they always use it to spawn. e.g. S. rastrifer, B. Ronchus
b) Occasional spawners
The spawning activity in the mangrove is merely occasional. This region can be used to spawn, but there is no evidence that a great number of individuals in this group of species use it. These species are not as abundant in the mangrove as those of regular spawners. e.g. C. parallelus, C. edentulus
c) Matures in system
The spawning activity of the species does not occur in the mangrove, but this region is frequented regularly during the final phase of maturation. e.g. I. Parvipinnis
d) Do not mature in system
The spawning activity does not occur in the mangrove, and the gonadal maturation, if present, does not occur in many individual. e.g. P. corvinaeformis, P. brasiliensis
The exact role of mangroves as nurseries are not well understood but a number of hypotheses have been proposed to explain this role (Robertson & Blaber 1992, Blaber 2000). The three main hypotheses are that mangroves provide juveniles with
(1) Refuge from predators
Numerous piscivorous fish enter mangrove during the high tide period (Blaber et al. 1989, Vance et al. 1996) thus smaller fishes escape their predators by entering in mangrove. This is attributed by various factors structural complexity of submerged vegetation, shallow water and turbidity can give significant refuges from predators, especially for small, mobile animals (Robertson & Duke 1987, Robertson & Blaber 1992).
Mangroves provide the protection from prey by structural complexity as mangrove habitat is very complex structurally because of pneumatophores and fallen debris (leaves, branches and logs), prop roots, buttresses and branches. These structures provide protection in various ways: by reducing prey visibility, by lowering encounter rate of prey and predator, and by limiting the ability of predator to search for and capture prey (Rönnbäck et al. 1999).
Shallow water condition does not favour the entry of large predators thus providing another form of refuse for small fishes and crustaceans (Boesch & Turner 1984, Blaber 2000). It has been observed at various places that small fishes and prawns moved into more shallow waters while larger predatory fishes remained in deeper water at the fringes of the mangroves.
High turbidity and shade beneath the mangrove canopy decreases the underwater visibility. The turbid and shaded water often found around mangroves may therefore provide an additional refuge from visual predators (Blaber & Blaber 1980, Whitfield 1999). Juvenile fishes get attracted to turbid areas and may use the turbidity gradient to locate nursery areas. Abundances of some fish species have been found to be higher in areas of higher turbidity (Blaber 2000).
Figure: Conceptual schematic diagram of the nutrient and energy fluxes in self-sustained mangrove ecosystem and the interaction of mangrove with adjacent freshwater and offshore marine ecosystem.
(Source: Islam & Haque, 2005)
(2) Abundance of food
Nutrient content and primary productivity are usually very high in mangrove area and food availability is more for fishes and crustaceans than any other coastal habitats. Nutrient comes to the mangrove system from upstream and from seaward and they are concentrated in mangrove area by trapping. Primary productivity in the mangrove forest itself attributed to several sources including epiphytes, phytoplankton, mangrove trees, and benthic microalgae (Rönnbäck 1999). Various fishes consume most of their feed when they come to the mangrove area. Primary productivity in mangrove forest forms the basis of a food web supplying abundant and varied trophic resources to higher consumers (Baran & Hambrey 1998).
Mangrove forest produce litter throughput the year, they have the ability to produce large quantities of litter, ranging from 10,000 to 14,000 kg dry weight/ ha/ year (Hamilton and Snedaker, 1984). Most creatures are unable to assimilate this directly and require bacterial enrichment before consumption. However, sesarmid crabs can directly consume mangrove litter and/or store 30–80% of the litterfall (Rönnbäck 1999). These crabs are eaten by fishes, creating a pathway for mangrove nutrients to enter food webs.
(3) Shelter from physical disturbances
Mangrove habitat is the area of low current, where impact of coastal tide gets reduced. This provides the small juvenile fishes benign physical environment to settle. Mangrove presence increases the residence time of water, especially in flat, wide mangroves with complex waterways (Wolanski & Ridd 1986).
The juveniles of few species of crustaceans, such as banana prawns Penaeus merguiensis and P. indicus ), are found exclusively in mangrove ecosystem (Staples et al. 1985, Vance et al. 1998, Rönnbäck et al. 2002) and are described as highly mangrove-dependent.
It has been established from various studies that about two third of world’s fish and shellfish harvest are directly linked to estuarine habitat (Robertson & Blaber 1992).
Rönnbäck (1999) listed the proportion of mangrove-related species in fisheries in various parts of the world:
% of fishes dependent on mangrove
Southeast Asian countries
Fish 30 (&Prawn 100%)
Products of Mangrove Ecosystem
(Source: Saenger et al, 1983)
Mangroves of Mumbai
Various studies confirm the destruction of mangrove throughout the globe and in particular have focused on estimating the total area cleared, rate of clearing, loss of sediments and erosion (Hatcher et al. 1989, Valiela et al. 2001, Alongi 2002).
Figure: Proportion of existing global mangrove areas and areas in the South and Southeast Asia
(Source: Islam & Haque, 2005)
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