Extent and Distribution
Mangroves are restricted to 30° North and 30° South latitude. However, the most northernly mangroves are located at 31°22.5’ N near the town of Kiire of Japan in the northern hemisphere and most southerly mangroves are located at 38°45’ S of Australia, where the mangroves exist below freezing point. ... Generally, mangroves dominate on the coast and the river banks up to which the tidal water ingress during high tide in the tropical and sub-tropical regions. The distribution pattern of mangroves is the result of latitudinal limit; particularly sea surface temperature, air temperature and inland rainfall. Globally there are two main centres of diversity of mangrove communities, the western and the eastern groups (Tomlinson, 1986). The eastern group correspond to the Indo-West Pacific regions which include central Pacific, East Africa, Indo-Malayan and Australasia. The western group correspond to Atlantic East Pacific regions which include the West African and American coasts of the Atlantic Ocean, the Caribbean Sea, the Gulf of Mexico and the western (Pacific) coast of America. These two regions have different floristic inventories. The Indo-West Pacific region has higher mangrove diversity, i.e. five times more diverse compared to the Atlantic East Pacific region.
Global Mangrove Cover
The total mangrove cover area of world is 152,361 sq. km (Giri et al., 2011). The mangrove cover has greatly decreased since the last century. Globally, it comprises less than 1% of tropical forest cover and 0.4% of total forest cover of world (FAO, 2006). ... Mostly mangroves are dominantly tropical forests and are found in the tropical region of South-east Asia, south Asia, North and Central America, South America, West and Central Africa and south Asia.Among them maximum area of mangroves is found in South-East Asia region over an area of 52,049 sq. km followed by South America region with 23,882 sq. km, North and Central America region with 22,402 sq. km and West and Central Africa region with 20,040 sq. km. The least mangrove cover is found in the Middle East with 624 sq. km.Figure 1.2. Pi chart showing mangrove cover in different regions.
In political perspective mangroves are found in 123 countries worldwide among which 12 countries comprise nearly two thirds of mangrove cover. Indonesia has maximum mangrove cover comprising 20.9 % of world total mangrove cover. Next to Indonesia, Brazil, Australia, Mexico, Nigeria, Malaysia, Myanmar, Bangladesh, Cuba, India, Papua New Guinea and Columbia have mangrove cover in descending order area wise (Table 1.1).
Table 1.1. Twelve countries with the largest mangrove area in the world, altogether comprising 68 percent of world’s total mangrove.
| Country | Mangrove Area (sq.km) | Proportion of Global Total |
|---|---|---|
| Indonesia | 29.9 % | |
| Jacob | 8.6 % | |
| Australia | 6.5% | |
| Mexico | 5.0% | |
| Nigeria | 4.8% | |
| Malaysia | 4.7 % | |
| Myanmar | 3.3 % | |
| Bangladesh | 3.2 % | |
| Cuba | 3.2 % | |
| India | 2.8 % | |
| Papua New Guinea | 2.8 % | |
| Colombia | 2.7 % | |
| Rest countries | 22.5 % |
MANGROVE SPECIES DIVERSITY
Mangroves represent a large variety of plant families, which are adopted to tropical inter tidal environment. Although mangrove is considered as tropical ecosystem unlikely other tropical ecosystems the diversity of mangroves is very low. Different researchers have classified mangroves in different classes taking different criteria. Saenger et al (1963) have classified mangroves into exclusive mangroves and non-exclusive mangroves based on mangroves habitat as well as elsewhere. He has considered 60 plants as mangroves out of which 48 are kept in exclusive mangroves group and rest in non-exclusive mangroves group. Tomlinson (1986) has classified mangroves in three groups based on exclusive position of plants in the estuary and other habitats such as (1) Major elements of mangal ('strict or true mangroves') (2) Minor elements of mangal and (3) Mangrove Associates. The major elements of mangal ('strict or true mangroves') possess all or most of the following features:- 1. Complete fidelity to the mangrove environment; that is, they occur only in mangal and do not extend into terrestrial communities.
- 2. A major role in the structure of the community and the ability to form pure stands.
- 3. Morphological specialization that adopts them to their environment; the most obvious are aerial roots, associated with gas exchange and vivipary of the embryo.
- 4. Some physiological mechanism for salt exclusion so that they can grow in sea water.
- 5. Taxonomic isolation from terrestrial relatives. Strict mangroves are separated from their relatives at least at the generic level and often at the subfamily or family level....
The minor elements of mangal are distinguished by their inability to form a conspicuous element of the vegetation. They occupy peripheral habitats and only rarely form pure communities. The Mangrove associates however, do not inhabit in habitat of strict mangrove communities, and may occur only in transitional vegetation and even exist as epiphytes. Based on above criteria Tomlinson has kept 34 species of 9 genus from 5 families under major elements mangrove, 20 species of 11 genus from 6 families in minor elements of mangroves.
Duke (1992) defines true mangrove more specifically as “a tree, shrub, palm, or ground fern generally exceeding 0.5 m in height and normally grows above mean sea level in the intertidal zone of tropical coastal or estuarine environments”. He has prepared an improve list of 69 mangrove species in 20 genera and 16 families in the world.
Kathiresan and Bingham (2003) have prepared a list of 65 species of 22 genera from 16 families which include Tomlinson's major and minor elements but not mangrove associates. They did not include three shrubby species; Acanthus illicifolius, Acanthus ebracteatus, Acanthus volubilis and two palm species; Nypa fruticans and Phoenix paludosa.
Most recently Spalding et al. (2010) in “World Atlas of Mangroves” have considered 73 species and hybrids as true mangroves. All these species have adopted to mangrove habitat. Out of 73 mangrove species, 38 species are considered as core species which typify mangroves and dominates in most mangrove ecosystems. The rest others are rarely abundant and more appropriately found on fringe of the mangrove habitats.
Polidoro et al. (2010) have considered 70 species as true mangrove based on Tomlinson's original list of major and minor mangroves supplemented by a few species added through the expanded definition provided by Duke (1992) and other new taxonomic additions by Sheue et al. (2003; 2009). This book follows Polidoro et al. (2010) list of mangroves. The list of true mangroves is given below (Table 1.2).
COUNTRY WISE MANGROVE DISTRIBUTION
Mangrove species distribution is not uniform worldwide. Maximum true mangrove species richness is found in South Asia, South-East Asia, Australia, New Zealand and Pacific Islands. ... Among the countries Indonesia has the maximum true mangrove species richness followed by Papua New Guinea, Philippines, Malaysia, Australia, India and Thailand.MANGROVES OF ODISHA
The Mangrove cover in India is about 3.3 % of worlds’ mangrove area and spread over an area of 4921 sq kms comprising 0.14% of countries total geographic area on its coastal states and islands in the Arabian Sea and the Bay of Bengal. ... Out of India’s total mangroves area very dense mangrove covers present over 1481 sq km, moderately dense mangrove 1480 sq km and open mangrove 1960 sq km.Mangrove cover of India for last one decade
The Sundarban on delta of the Ganges and the Brahmaputra of West Bengal accounts more than 40% of mangrove cover of India over an area of 2114 sq km. Gujrat has 2nd largest mangrove cover in the country over an area of 1140 sq km, followed by Andaman & Nicober Islands with of 617 sq km, Andhra Pradesh with 404 sq kms, Maharastra with 304 sq km and Odisha with 243 sq km of mangrove cover (FSI Report – 2017). In India the mangrove area is increasing over the years. ...Pi Chart showing mangrove cover in percentage state and UT wise.
The maritime state Odisha has a coast of 480 km long coast. The beach of Odisha coast has been broken by various river mouths putting water into the Bay of Bengal. The major rivers of Odisha such as The Mahanadi, the Brahmani, the Baitarani, the Subarnarekha form estuary on their mouth region before falling into the sea. Mangrove exists on these river estuaries from the time immemorial guarding the hinterland against various vagaries of nature such as tropical cyclone, tsunami etc. The coastal districts Baleswar, Bhadrak, Kendrapara, Jagatsinghpur, and Puri has conspicuous mangrove on coastal tracts. Kendrapara district has the maximum 197 sq km of mangroves cover. The Bhitarkanika National Park and Bhitarkanika Wildlife Sanctuary and buffer zone of Gahirmatha Marine Sanctuary encompasses maximum mangrove areas of this district providing protection. North to Bhitarkanika the mangrove areas of Bhadrak district lies on the sea front and some offshore islands. In Baleswar district the mangroves are found on the estuary formed on the mouth region of the Subarnarekha river and known as Bichitrapur mangroves. On the estuary formed by the Devi river in Jagatsinghpur mangroves are present. In Puri very small patches of mangroves are found in southern bank of the Devi river mouth and in Chilika.
| Districts | Very Dense Mangrove in km2 | Moderately Dense Mangrove in km2 | Open Mangrove in km2 | Total Mangrove Area in km2 |
|---|---|---|---|---|
| Baleswar | N/A | 1 | 4 | 5 |
| Bhadrak | N/A | 9 | 23 | 32 |
| Jagatsinghpur | N/A | 1 | 7 | 8 |
| Kendrapara | 82 | 83 | 32 | 197 |
| Puri | N/A | N/A | 1 | 1 |
| Total | 82 | 94 | 67 | 243 |
Although Odisha has less mangrove cover to West Bengal, Gujrat, Andhra Pradesh, Karnataka in Indian mainland, the mangrove diversity is highest. The Andaman and Nicobar Islands has a total of 38 true mangrove species belonging to 19 genera and 13 families whereas Odisha has 35 true mangrove species belonging to 20 genera and 14 families ( Ragavan et.al., 2016) highest in Indian main land. Chadha and Kar
Mangrove species richness Indian states and Union territory wise
Mangroves in Odisha has been concentrated in three major areas i.e. Bhitarkanika, Mahanadi Delta and Devi Estuary. Apart from these areas Subarnarekha mouth has some good chunk of mangrove stand and Chilika lake has newly planted mangroves on its mouth region although there were record of mangrove vegetation in past. ... During our study we found that Bhitarkanika has maximum mangrove diversity followed by Mahanadi delta and Devi Estuary. Bhitarkanika has 33 true mangrove species and more than 40 mangrove associates whereas Mahanadi delta has 29 true mangrove species and more than 20 mangrove associates. The Devi Estuary has 19 true mangroves and more 17 mangrove associates while Chilika Lake has only 6 true mangrove species which were planted.At present the mangrove cover is only one third of the past mangrove cover of 1930s (Das, 2010). There rampart cutdown of mangrove trees for human settlement expansion as well as industrial development on the coast was the main reason behind this decrease of mangrove cover. The removal of mangrove from the coast has made the human settlements in the hinterlands prone to natural calamities coming from sea.
Bhitarkanika
The mangrove ecosystem of Bhitarkanika has been notified as Bhitarkanika Wildlife Sanctuary which covers an area of 672 km2. The sanctum sanctorum of Bhitarkanika Wildlife Sanctuary is designated as Bhitarkanika National Park with an area of 145 km2 of pristine mangroves. This stretch of mangrove is relatively well preserved and protected. In Bhitarkanika, the mangrove formation is seen along the creeks, channels and islets. ... The floral diversity of Bhitarkanika includes a total of 302 plant species belonging to 80 families, 93 plants are monocotyledon belonging to 18 families and 209 plants are dicotyledons belonging to 62 families (Banerjee, 1984). Chadha and Kar (1998) has recorded 71 numbers of mangrove and associate species.Generally, the two-storey system is observed in this mangrove forests since the ground flora is very poor. The dominant mangrove taxa constituting the top canopy are Rhizophora spp., Bruguiera spp., Sonneratia spp., Avicennia spp., Excoecaria agallocha, Heritiera spp., Cerbera odollam, etc. Soneratia apetala and Avicennia spp. are gregarious and luxuriant, colonising the banks of river and creeks. Xylocarpus granatum is sometimes observed in this habitat. Pongamia pinnata is also found in abundance, usually away from the water bodies. Phoenix paludosa, Thespesia populnea and Tamarix troupii in the peripheral regions where tidal inundation is irregular. In Bhitarkaika Forest Block, on elevated regions where tidal inundation is irregular there top canopy is formed by Diospyros malabarica. The second storey is composed of the shrubby elements and under-trees such as Brownlowia tersa, Kandelia candel, Lumnitzera racemosa, Ceriops decandra, Cynometra iripa, Clerodendrum inerme, Aegiceras corniculatum, Caesalpina crista and Hibiscus tiliaceus. These elements flourish where there is tidal influence as well as a high degree of salinity. B. tersa is plentiful along the fringes of water bodies and remains half-submerged in water. Like-wise, Rhizophora spp. trees with their interwoven knee roots are observed in the muddy flats. In the terrestrial and swampy areas (Flagellaria indica, Salvadora persica, Salacia prinoides, Azima tetracantha, Phoenix paludosa, etc. are quite common. Common climbers of this mangrove forest are Derris trifoliata, Derris scandens, Finlaysonia obovata, Sacrolobus globosus, Pentatropis capensis and Mucuna gigantea, etc. The ground flora which is very rare in Bhitarkanika mainly compose of Suaeda spp., Sesuvium portulacastrum and Salicornia brachiate. Mostly these species occur as indicator of degraded mangrove and accompany with dieback of top storeyed and mid storeyed mangrove tress. The elevated areas surrounded by the mangroves which are not inundated by tidal water regularly and have sandy soil have terrestrial plant such as Manikara hexandra, Ficus retusa, Ficus religiosa, Ficus virens, Toddalia asiatica, Ixora arborea, Zyziphus oenopila etc.
Among the creeks usually on the rear edge where salinity is low due to higher amount of freshwater inflow Acrosticum aureum and Acanthus ilicifolius are seen in close association. The spiny element Caesalpinia crista is also not uncommon in such localities. The ground flora is rather very poor. Usually in the muddy flats, Myriostachya wightiana is found in pure formation. Porteresia coarctata is also found in patches on creek banks. Other notable herbaceous elements are Suaeda maritima, S. nudiflora, Salicornia brachiata, etc. Tylophora tenuissima, Fimbristylis spp. etc. are found in more dry and elevated areas.
The offshore islands on the periphery of Bhitarkanika such as Kanika sands, Babubali, Mahakurdia and riverine island Kalibhanjadia has rich mangrove diversity.
Mangroves are highly site specific. The terrine of Bhitarkanika is crisscrossed by a number of creek and rivers with varied distance from sea and elevation subjected the mangroves with varied degree of tidal inundation, salinity and silt deposition rate, providing a great number of plant habitats. On suitable ground different mangroves form different communities based on their requirements. These some plant communities formed solely by single species or single genus forming pure patches. Examples of such communities are Avicennia community, Avicennia-Excoecaria community, Excoecaria community, Heritiera community, Phoenix community etc.
In Bhitarkanika there some plants were earlier reported but during our study from 2013 to 2018 we are unable to locate Sonneratia griffithi, Acanthus volubilus, Lumnitzera littorea, Tamarix ericoides. The plant claimed to be endemic to Bhitarkanika, Heritiera kanikensis is also not found and on literature survey if is found that Kathirsen (2010) has claimed nonexistence of such species in Bhitarkanika. In this website we have described 33 true mangrove species and 46 mangrove associate species following the APG III system of flowering plant classification present in Bhitarkanika national Park.
Mahanadi Delta
The Mahanadi delta is a species rich mangrove ecosystem of the country. Paradeep, Jambu, Batighar, Kharnasi and Hukitola offshore island have mangrove cover. Presence of a number of meandering interconnected creeks, water channels, islands and islets with regular tidal flush and continuous discharge of sufficient amount of fresh water throughout the year create suitable niches for the development of luxuriant mangroves. ... Total mangrove cover in Mahanadi delta is 45 km 2 of which 27 km 2 mangrove area is included in the buffer zone of Gahirmatha Marine Sanctuary. Twenty-nine true mangrove species and more than 30 mangrove associates have been reported so far from Mahanadi delta by various workers Two mangrove species of Mahanadi delta are at elevated threat of extinction globally; Sonneratia griffithi is critically endangered (CR), and Heritiera fomes is endangered (EN) as per IUCN Red List. Apart from these two elevated threatened mangroves Phoenix paludosa, Brownlowia tersa, Aegialitis rotundifolia and Ceriops decandra are listed as near threatened (NT) in Red List (Polidoro B A, 2010) which are present. During our study of last five years we are unable to locate Sonneratia griffithi in Mahanadi delta. The southernmost distribution of Heritiera fomes is Hikitola island in Indian sub-continent. The vegetation in the Mahanadi delta is denuded due to the construction of Paradeep Port (1965) and the Paradeep Phosphate factory and construction of residential complexes and other industrial complexes. Many species have been wiped out and some are on the verge of extinction. The list of mangrove and associate species present in Mahandi delta id given in Table X.X.In the Devi estuary, a good patch of mangrove forests is observed. The top canopy consists of A. officinalis, S. apetala, B. gymnorhyza, E. agallocha, K. candel and C. decandra, etc. The second storey consists of shrubby elements like A. corniculatum, A. ilicifolius, Dalbergia spinosa, P. paludosa, T. troupii, H. tiliaceus, C. inerme, etc. In the mud-flats, P. coarctata and M. wightiana are gregarious. The notable climbers are D. scandens, Derris trifoliata. Among the sand dunes C. crista, S. littoreus, Solanum trilobatum, Ipomea pes-caprae, Sesuvium. portulacastrum etc. are worth mentioning.
Devi Estuary
In the Devi estuary, a good patch of mangrove forests is observed. The top canopy consists of A. officinalis, S. apetala, B. gymnorhyza, E. agallocha, K. candel and C. decandra, etc. ... The second storey consists of shrubby elements like A. corniculatum, A. ilicifolius, Dalbergia spinosa, P. paludosa, T. troupii, H. tiliaceus, C. inerme, etc. In the mud-flats, P. coarctata and M. wightiana are gregarious. The notable climbers are D. scandens, Derris trifoliata. Among the sand dunes C. crista, S. littoreus, Solanum trilobatum, Ipomea pes-caprae, Sesuvium. portulacastrum etc. are worth mentioning.
Bichitrapur Mangroves
The Subarnarekha estuary is endowed with a few species of mangroves such as A. alba, A. officinalis, A. marina, A. corniculatum, E. agallocha, R apiculata, R. mucronata, S. apetala and A. illicifolius etc.
Chilika
In the past, the margin of the Chilika lake and the undisturbed islands like Badokuda, Sanokuda, Ghantasila, etc. were endowed with the unique eco-system of mangroves. ... But in the course of time, the mangroves have been replaced by tidal scrub jungles and only some mangrove associates are present due to the change of the eco-climatic conditions coupled with the ruthless cutting of trees by the local inhabitants to cater for their various needs. The vegetation is totally devoid of the true mangrove species and only a few associates are encountered in the denuded regions. Recently in past one decade, there efforts were taken to reintroduce by plantation of R mucronata, R. apiculata, A. alba and A. marina in Chilika, particularly in the mouth region of outer channel.