Biogeography of Indian Mangroves
The Indian coastline of about 5,700 km long can be divided into the east and west coasts and island chains. The east coast covers the maritime states like Tamil Nadu, Andhra Pradesh, Orissa, West Bengal and Andaman-Nicobar Islands. The West coast extends from Kerala, Karnataka, Goa, Maharashtra, Gujarat and also includes the coral atolls of Lakshadweep Islands. The total mangrove area along the Indian coast is estimated to be approximately 700,000 ha. The mangroves along the east coast of India is more (80%) than that of west coast (20%) because the terrain of the east coast has a gradual slope as plains compared with the steep gradient along the west coast.
West Coast of India
Mangroves of Gujarat coast
Gujarat is the north western state of India and the total length of the coast line, facing the Arabian Sea is about 1600 km; situated within the longitude 68o E and 73o E and latitude 20o 10' N and 23o 10' N. Based on the geographical situation geomorphological position and variable natural land, the Gujarat coastal zones may be divided into 5 regions
- The Rann of Kachchh
- The Gulf of Kachchh
- The Gulf of Khambhat
- The Saurashtra coast
- The South Gujarat coast
Out of these five regions , the Gulfs constitute the major mangrove zones of the Gujarat Coast. Several minor rivers, viz. The Luni, the Mahi, the Narmada the Tapti and the Gulf of Kachchh as well as Gulf of Khambhat have divided the entire coastline, where the highest tidal amplitude (tidal bore) rises upto 10.2 m from the Mean Sea Level at Bhavnagar.
Rann of Kachchh : This area is the extreme western part of India and is divided into two regions i.e. Great Rann, which covers about 10,500 km2 and Little Rann, which covers about 3,000 Km2. Both these regions are saline desert along with arid climate, though during monsoon months i.e. July to September, this area is inundated with the upstream sea water flow along with tidal ingress from several minor creeks, water ways and canals.
Gulf of Kachchh : This region is extended between the latitude 22o 15' N and 23o 00 N and longitude between 69o 00 E and 70o 30 E. It has 2,483 ha and 12,800 ha mangrove zones in the northern coastal and southern coastal zones respectively in the Gulf of kuchchh. This extensive Gulf of Kachchh contains both mudflats islands with fringing coral reefs and scattered mangroves. Gujarat government has declared 455.92 km2 area as Marine Sanctuary from Okha to Jodiyar. An area of 162.89 km2 area at at Pirotan Island is notified as 'Marine National Park". This 'Marine National Park' is very much important ecologically, with its unique coral reefs, mangroves and other interesting marine flora and fauna.
Saurashtra coast or Kathiawar : Several islands, tidal flats, minor estuaries, embayments and beaches and rows of dunes are also present along the Saurashtra coast.
Gulf of Khambhat : This zone lies between the latitude 20o 30 N and 21o 30 N and longitude 70o 00 E and 73o 00 E. This Gulf area is characterized by the estuaries, like the Sabarmati, the Mahi, the Kim, the Dhandhar and the Tapti; Extensive mud flats, dunes, scattered sandy beaches makes this Gulf very much diverse ecotype. Because of the diverse nature and number of estuaries, these zones are also known as "estuarine delta"
South Gujarat coast : This coast line is broken by several small tidal creeks and few minor estuaries, like the Mindhola, the Purna, the Ambica, the Auranga, the Daman Ganga. Mudflats and marsh vegetation is also present
Mangroves of Maharashtra Coast
The total length of the Maharashtra coast is characterised by several pocket beaches flanked by rocky cliffs, these are estimated about 720 km long. The 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 from South to North
- Thane District
- Sindhudurg District
- Ratnagiri District
- Raigad District
- Bombay District
Thane District. Here the mangrove zones are much degraded. During the last 25 years about 40% mangrove area in the Maharashtra coast reduced for constant anthropogenic pressure.
Satellite Imagery data shows that in Maharashtra coast the mangrove area is only 148.4 km2 on the mouth rivers like the Vashishti, the Thane, the Vaitarana. The minor areas are Ratnagiri, Raigad, Thane, Bombay, Sindhudurg, Mahim, Elephanta Island, Waghotan, Rajapur, Dharamtar, Vasai (Ulhas), Shastri, Vikroli etc.
Mangroves of Goa Coast
This coastal region is situated in the Central-West Coast of India, facing the Arabian sea and extended North to South. The total length of the coast line of Goa is approximately 120 km and within the latitude 150 00'N - 150 52'N and longitude 730 30'E - 740 44'E. The inter-tidal zones of seven minor estuaries are mostly flanked on both sides by the rocky cliffs and formed with silty-sand and silty-clay along with abundant organic matters.
The minor estuaries in this coastal zone are
- The Terekhol
- The Chapora
- The Mandovi
- The Zuari
- The Sal
- The Talpona
- The Galgibag
Beside these the connecting Kumbharjua canal links both the Mandovi and Zuari. The soils are mostly alluvial and lateritic soil with high percentage of Iron (Fe) and Manganese (Mn).The major mangrove zones are extended in the Zuari estuary and Mandovi estuary and the other sporadic mangrove patches are distributed in the remaining 4 estuaries and the Kumbharjua cannal connecting Mandovi and Zuari estuaries.
Chodan (Chorao) Island : This is the totally protected mangroves are 160 ha. near the village of Chodan (Chorao) . This mangrove forest has been declared as Dr. Salim Ali Bird Sanctuary. It harbours good mangrove flora, comprising about 12 mangrove species and 8 associated species.There are no major anthropogenic threats. The nearby area of almost 80 ha is under pisciculture.
The whole sanctuary area consists of mangrove vegetation interspersed with water channel, having tidal variations. The area is very rich in marine fauna and avifauna.
Fauna : Total area of the sanctuary consists of mangrove forests with varieties of fauna. The area is marshy, criscrossed with a network of water channels having tidal effect. This area is well suited for estuarine fishes and other marine fauna. Other fauna reported are Jackal, Python, Flying Fox, Otters and birds like Brahminy Kite, White Bellied Fishing Eagle, Parish Kite, Kingfisher, Grey Heron, Pond Heron, Reef Heron, Sand Piper, Cormarant etc. There are many associated mangrove species also.
Mangrove forest : Rhizophora mucronata, Bruguiera conjugata, Excoecaria agallocha, Sonneratia apetala, Avicennia officinalis, Aegiceras majus, Derris scandens, Salvadora persica, Acanthus illicifolius, Clerodendron inermes.
Mangroves of Karnataka Coasta
Karnataka state lies between latitude 11 12' N - 18 12'N and longitude 73 48' E - 78 18' E. It coveres a geographical area of about 1,90,4983 sq.km. The coastline is about 320 km long and is overshadowed by the Western Ghats mountain range. There is a narrow strip of varying width between the mountain and the Arabian Sea the average width being about 20 km. The coast is lined with sandy and occasionally rocky shores. The average height of the hinterland is 70 - 75 meters, but in some places it can be as high as 150 meters.
Mangroves in Karnataka are of fringing type, found in the intertidal regions along the estuaries, backwaters, islands and other protected areas. The distribution of mangrove forest depends on the intertidal expanse, tidal range, substratum, salinity of soil and water.About 14 species of mangroves belonging to 9 genera under 7 families are found along the estuaries of the Karnataka coast. The dominant species are , Avicennia officinalis, Avicennia marina, Rhizophora conjugata, Rhizophora mucronata, Acanthus ilicifolius, Clerodendron inerme.
In coastal karnataka, mangroves are found growing along the rivers like Kalinadi, Belamdar nadi, Gangavali and Agnashini.Dense mangrove consisting of very old trees of R. mucronata, S. caseolaris and A. officinalis are found along river Sharavati, mostly at Karki, Haldipur, Dhareshvar, Honavar.
The dense mangroves vegetation is present at Coondapur, particularly in the confluence zone of the three rivers namely Chakra, Kollur and Haladi, just before they open into the Arabian Sea.. In this estuarine complex an area of about 30,700 m2 is occupied by mangroves. The floral element in Coondapur are are R. mucronata, R.
conjugata, Avicennia officinalis and Acanthus ilicifolius.
Mangroves of Kerala Coast
The length of the Kerala coast is about 560 km, extending from north to south with parallel to the ?Western Ghat? The higher population density in the Kerala coast has resulted tremendous pressure on the natural ecosystem. For urbanization, construction of harbours, ports, prawn farming, coconut plantation and rice-fish culture vast mangrove lands were cleared or reclaimed.
East Coast of India
The mangrove ecosystem of the East coast of India are mostly deltaic type and distributed in 5 major deltas as well as estuarine mouths of 4 maritime state viz. Tamil Nadu. Andhra Pradesh, Orissa and West Bengal
Mangroves of Tamil Nadu Coast
The coast line of Tamil Nadu extends about 950 km, within thelatitude8 N-13 30?N and longitude 77 15?E ? 80 20?E. with about 46 big and small rivers. All these rivers carry freshwater and silt particles from the upper reaches and discharge in the coastal zone. Mangroves in the Tamil Nadu comprises in the Cauvery delta complex, Pichavaram, Muthupet and Chattram area. The common dominant mangroves are Rhizophora apiculata, Rhizophora mucronata, which attains 5-7 m height and the occasional mangroves are Sonneratia apetala, Avicennia marina, Avicennia officinalis, Bruguiera cylindrica, Ceriops decandra, Aegiceras corniculatum, Lumnitzera racemosa.
The Back mangals are Derris trifoliata, Dendrophthoe falcata, Suaeda maritima, Suaeda monica, Sesuvium portulacastrum, Heliotropium curassavicum, Salicornia brachiata, Excoecaria agallocha, Acanthus ilicifolius, Clerodendron inerme, Solanum trilobatum, Cyperus arenarium, Fimbristylis cymosa, Aeluropus lagopoides
Latitude : 11o 27'N
Longitude : 79o 47' E,
Estaury : Delta of Vellar and Coleroon estuarine systems
Situated about 250 km South of the city of Madras, on the south east coast of India. It is located in the Vellar-Coleroon estuarine complex and has many islands separated by intricate water-ways. It covers an area of about 400 hectares and is traverced by a large number of channels and creeks which connect the Coleroon estuary in the south and Vellar estuary in the north.
The common dominant mangroves are Rhizophora apiculata, R. mucronata, which attain 5-7 m height and the occasional mangroves are Sonneratia apetala, Avicennia marina, A, officinalis, Bruguiera cylindrica, Ceriops decandra, Aegiceras corniculatum.
The Cauvery river is the main riverine system of the Thanjavar District, with the following cannels viz. Paminiyar, Korayar, Kilaithangi, Kanthapridan, Marakakorayar and Valvanar. In this area Avicennia marina, Excoecaria agallocha, A. corniculatum are the dominant mangrove flora.
Gulf of Mannar
This marine Biosphere Reserve along the coast of Tamil Nadu, is first of its kind in India and southeast Asia. It is situated in the Indian part of the Gulf between India and Sri Lanka. It covers an area of about 10,500 sq.km., running southeast and parallel to the main coastline to a distance of about 170 nautical miles. It is an area of about 21 islands from the northern most Pamban to Tuticorin. The total island area is about 555 ha.
Latitude : 8° 35' - 9° 25' N
Longitude : 78° 8' - 79° 30' E
The Gulf is influenced by both south west (from April to July) and north east (October to Decmber) monsoonal rains
The Gulf of Mannar and the islands posses unique mangrove vegetation along with other flora and fauna . The vegetation consists of species belonging to Rhizophora, Avicennia, Bruguiera, Ceriops, Lumnitzera etc. Although mangroves are reported from majority of the islands, this vegetation of Manalli is striking for its luxuriance and diversity. They are not very tall trees, perhaps the height is reduced due to strong winds lashing here perennially and with greater velocity during monsoons, periodical cyclones etc. The species includes plants of Avicennia officinalis, Excoecaria agallocha, Bruguiera cylindrica, Ceriops tagal, Lumnitzera racemosa . Many halophytes like Suaeda maritima, Suaeda monoica, Arthocnemum indicum, Sesuvium portulacastrum, etc. are also found.
Mangroves of Andhra Pradesh Coast
Total length of Andhra Pradesh coast line is about 1014 km, rocky and sandy coast and mangroves are present in the deltas like Godavari and Krishna. These are situated within the latitudes between 13 30?N and 19 00?N and longitude between 80 05?E and 85 05?E.
The major estuaries viz. Godavari and Krishna from the deltas in the coastal areas of Andhra Pradesh. The Godavari is the second longest river in India with a length of 1,530 km and it has 16 major tributaries. The Godavari divides into two major distributaries viz. Gautami-Godavari and Vasishtri-Godavari. The river Godavari is the border line between the mangroves of Sundarbans ? Mahanadi delta and mangroves of Peninsular India.
The mangrove species like Rhizophora spp. Avicennia marina. Avicennia officinalis, Ceriops decandra, Bruguiera gymnorrhiza, Lumnitzera racemosa, Sonneratia apetala, Excoecaria agallocha, Acanthus ilicifolius, Suaeda nudiflora are reported from this area. The grass species like Porteresia coarctata, Myriostachya wightiana are often noted as grazing material for cattle.
From Krishna delta Rhizophora mucronata, Rhizophora apiculata, Bruguiera gymnorrhiza, Excoecaria agallocha, Lumnitzera racemosa, Suaeda monioca, Suaeda nudiflora, Suaeda maritime, Salicornia brachiata, Arthrocnomum fruticosm, Bruguiera conjugata, Bruguiera caryophylloides, Sonneratia apetala, Xylocarpus molluccensis and several other species are reported.
Mangroves of Orissa Coast
The total length of this coast line in Orissa is about 430 km and this coast line is mainly in the depositional stage with the sediments carried down by the river Mahanadi with 853 km length and other two minor rivers viz. Brahamani and the Baitarani. All these rivers form deltas in the Orissa coast ie. Bhitarkanika. The coastal zone is situated between the latitude 19 N and 22 N and longitude between 85 E and 87 30?E.
Species like Avicennia alba, Avicennia officinalis, Excoecaria agallocha, Heritiera fomes, Sonneratia apetala, Rhizophora mucronata, Rhizophora apiculata, Ceriops decandra, Bruguiera parviflora, Aegiceras corniculatum, Phoenix paludosa and Porteresia coarctata are the dominated species of Bhitarkanika
Sundarbans Biosphere Reserve : The total geographical boundary of the Indian part of the Sundarbans is 9630 km2, within the latitude between 21o 30'N and 22o 15'N and longitude between 88o 10'E and 89o 10'E, which spread over the southern parts in the districts 24-Parganas (South) and 24-Parganas (North) of the West Bengal. the Sundarbans mangrove ecosystem in India spread over an area of 4266.6 km2 of the estuarine tracts of the Ganga Brahmaputra system. Six principal estuarine rivers viz. Baratala, Saptamukhi, Thakuran, Matla, Gosaba and Herobhanga are connected with Bay of Bengal in their southern extremities. These tidal estuarine mouths sometimes 6 km broad, which carry the tidal sea water and inundate these Sundarbans mangrove forest in regular intervals. Most of the estuarine rivers of Sundarbans have lost their earlier connections with the river Ganga and their tidal water turned saline. As such the virginity of these mangrove forests have been torned.
The total land area of the Indian Sundarbans mangrove forest at present is about 2300 km2 under 56 islands and the total water spread area .
The area falls under the inter-tidal zone and has a tropical humid climate. Annual average rainfall is 1900 mm. Average salinity of water varies from 1.11% on east and 2.37% total salt on west. Average tidal amplitude is 2.1 m. which reaches its peak during the stormy months of March/April. Based on the physiographic characters of different delta lobes, the Sundarbans Biosphere Reserve can be divided into 6 zones
- Sagar-Mahisani-Gharamara-Sand group of islands at the estuarine mouth of Hoogly river
- Mahisani island on west and Thakuran river on east
- Zone between the river Thakurana dn Matla
- Core area of Sundarbans Tiger Reserve
- Buffer are of Sundarbans Tiger Reserve
Area lying east of Matla river
Sagar-Mahisani-Ghoramara-Sand Head group of islands (Zone I)
These islands are essentially recent ones made of sandy upper strata, situated at the estuarine mouth of river Hoogly over an area of 90 sq.km. About 15 sq.km. would be restoration zone and 75 sq.km. would be manipulation zone (Agriculture). The salinity of the soil in these sandy islands is reduced by leaching. There lies a sewwt water lense at a depth of 40 ft. which made this part more attractive. Winder irrigation in a small scale could give rise to large scale rabi production of water melon and chilli. The sweet water of river hoogly has the only influence in this zone and owng to release of water from the Farakka barage, there has been some changes in the salinity regime. The islands show signs of natural regeration of Heritiera fomes. Other effects demand urgent investigation.
Mahisani island on west and Thakuran river on east over an area of 900 sq.km. (Zone II)
This area covers 200 sq.km. of restoration zone and 700 sq.km. of manipulation zone (Agriculture). This is the second delta lobe of the 5 lobed Sundarbans delta. This zone is characterised by a transitional effect of lack of sweet water flow. The planktonic production shows a preponderance ofCapepadas (Zooplnakton) and Diatoms (Phytoplankton) typical of sheltered estuary. The aquaculture activities are more restricted to silvopisciculture than agro-pisciculture. Silvopiscicultural farms for rearing Tiger Prawn has been set up by Forest Department. The Kakdwip island prawns are reared in controlled conditions in this zone. There is a crocodile breeding farm at Bhagabatpur island and a wild life santuary at Lothisn island.
The zone between the rivers Thakuran and Matla over an area of 1600 sq.km. (Zone III)
The portion of delta lobe is completely detached from any upstream flow and is facing the undeterred effect of rushing back waters. The area of forest is 1400 sq.km. which falls within manipulation zone (Forestry) and restoration zone would be around 30 sq.km. out of the forest area which is highly degraded state on northern portion. Balance 200 sq.km. would be the manipulation zone (Agriculture). The aquaculture here comprise of a combination of silvo and agropisciculture. Sundarbans Development Board has already stated a silvopiscicultural farm over a large area in Herobhanga island. Restoration of northern forest blocks is badly necessary by enrichment planting augmented protection and curbing export of forest produce to metropolis. The area of 1400 sq.km. mangrove forests needs immediate conservation approach until it is too late and the area turns into Phoenix swamps as a biotic subclimax.
The area of Sundarbans Tiger Reserve's core area lying between the rivers Matla in west, Haribhanga on east and on the north bounded by the rivers Netidhopani and Gosaba over 1700 sq.km. area where interference is already minimum, will serve as the 'Core zone' of Biosphere Reserve. An area of 1330 sq.km. has already been declared as National park in order to ensure strict legal protection.
The buffer zone of Sundarbans Tiger Reserve over 885 sq.km. would come under manipulation zone (Forestry). This area holds a game sanctuary over 365 sq.km. mangrove forests. This is the exploitation zone of Sundarbans Tiger Reserve based on the sound principles of conservation management. This area thus need to be continued as an example of manipulated forests with conservation approach. The eastern end of the forest receives a tickle of sweet water flow from the river Ichhamati, unlike the forest under zone III.
The area north of forest area lying to the west of river Matla.
This zone receives some trickle of sweet water from the Ichhamati river and is traditionally practising Aquaculture, Agrofishery etc. This zone would naturally fall within the manipulation zone (Agriculture) over an area of 4455 sq.km. Unlike all other zones, this area is relatively more advanced in agriculture and aquaculture. The lions share of Tiger Prawn comes from this zone. Agro-fishery has received lot of public support within this relatively less saline creek areas. The easterly flowing effect of Ganges through tributaries of river Padma makes the area more characteristic within the proposed Sundarbans Biosphere Reserve.
The area is a unique highly productive mangrove ecosystem and is the richest mangrove repository of India. It is the home of number of endabgered and threatened species of plants. Some of the mangrove species are Avicennia alba, Excoecaria agallocha, Ceriops decandra. All mangrove flowers are nectar bearing and Sundarbans produces 50-60m tomes of honey every year. 29 species of mammals, 144 species of birds, 55 species of reptiles and 7 species of amphibians have been recorded in Sundarbans. The enfangered animal species are Royal Bengal Tiger, Fishing Cat, Gangetic Dolphin and King Crab.
People, landuse and socio-economics Nearly 24 lakh people now depend on the area under Sundarbans Biosphere Reserve. The reclaimed intertidal lands are single crop lands for paddy where winter-irrigation is not possible from saline tidal waters. Hence, people have to depend on aquaculture, fishing, honey collection and wood cutting even bearing the man eating tigers. As a result, people here live much below the poverty line..