A mangrove refers to the tidal forest or individual plant or both1, 2. The term “mangroves” is used for intertidal plants and plant communities of the intertidal forest community called ‘Mangal’3. Different workers considered ‘mangrove’ to refer to plants growing in the highest and lowest tidal areas1,4-12. Mangroves are a taxonomically diverse group of salt-tolerant, mainly arboreal, flowering plants13. Mangrove are present around 118 countries and spread 137,760 km2 during the year 2000 in the tropical and subtropical regions of the world, Asia (43%) followed by Africa (21%), North and Central America (15%), Oceania (12%) and South America (11%). In the world 15 countries (Indonesia 22.6%; Australia 7.1%; Brazil 7.0%; Mexico (5.4%; Nigeria 4.7%; Malaysia 3.7; Myanmar 3.6%; Papua New Guinea 3.5%; Bangladesh 3.2%; Cuba 3.1%; India 2.7%; Guinea Bissau 2.5%; Mozambique 2.3% Madagascar 2.0% and Philippines 1.9% occupied 75%14. Total global mangrove areas ranges from 110,000 to 240, 000 km2 15,16.
They grow in extreme temperature, high salinity, high sedimentations, high tides and muddy anaerobic soils. Mangroves are an important ecosystem, contributing to energy flow between land and sea and also providing vital ecosystem services; including waste processing, coastal protection, biodiversity enrichment food production and recreation17,18. The mangroves also strongly influence the structure of neighboring marine communities by increasing the biomass of commercially important fish and invertebrates that spend part of their life cycles in the mangrove environment emphasizing the nursery function of mangroves19,20,21.
Tamil Nadu has an extensive coastline and a vast exclusive economic zone (EEZ) with Pulicat Lake in the north and Kanyakumari in the south. Mangroves have not been surveyed in all parts of Tamil Nadu, especially in estuarine systems. Hence, in the present study the mangroves and associates were surveyed along 56 estuaries of Tamil Nadu. For survey of many estuaries, the number mangroves species may increase.
Materials and Methods
A survey has been made during 2012-2014 on the true mangroves and their associates along 56 estuaries of Tamil Nadu (Fig. 2). The coastline was divided into five different groups such west coast of Tamil Nadu (3 estuaries), Gulf of Mannar (10 estuaries), Palk Bay (13 estuaries), South Coromandel coast (13 estuaries) and North Coromandel coast (16 estuaries). The mangroves and associate vegetation were identified following the standard references of10,18,22-25.Nomenclatures of the identified species were checked with the International Plant Names Index (IPNI). Species not recorded shows minus (-) symbol, present shows one plus (+) symbol, it means species available 1-3 sites; co-abundant shows two plus (++) symbol, it means species recorded 4-6 sites; abundant shows three plus (+++) symbol, it means species found 7-9 sites; dominant shows four plus (++++) symbol, it means species observed above 9 sites.
Results
A total of 39 species of mangroves and mangrove associate species were reported in 56 estuaries. The highest number of mangroves and associates (31) was observed in the North Coromandel coast, followed by Gulf of Mannar (23), South Coromandel coast (20), west coast of Tamil Nadu (19) and Palk Bay region (17).
A total of 16 mangroves belonging to 11 genera and 9 families were recorded along the Tamil Nadu coast. Fourteen mangrove species were observed in the North Coromandel coast, six species from South Coromandel coast, six species from the Gulf of Mannar, five species from West coast of Tamil Nadu, two species from the Palk Bay region. Nine of the 16 mangrove species belonged to two families: six in Rhizophoraceae and three in Avicenniaceae. Avicennia marina was the most dominant mangrove species in North Coromandel coast and co-abundant species in Gulf of Mannar, Palk Bay and South Coromandel coast. Bruguiera gymnorrhiza was only reportedin the Ariyankuppam and Thengathittu estuary of northern part of Coramandel coast and Avicennia alba was reported only in Palayakayal estuary of Gulf of Mannar coast. Among the mangrove plants, Rhizophora annamalayana, Bruguiera cylindrica, B. gymnorrhiza, Ceriops decandra, Lumnitzera racemosa and associate species Derris trifoliata, Xylocarpus mekongenesis, Thespesia populnea, Heritiera littoralis were noted as species specific to the North Coromandel coast (Table 2).
Mangrove associates (23 species) belonging to 21 genera and 17 families were recorded. The North Coromandel region and Gulf of Mannar were reported with more number of species (17 species), followed by Palk Bay (15 species), west coast of Tamil Nadu (14 species) and southern part of Tamil Nadu (14 species). Number of species were greatest in the in Chenopodiaceae family (5 species), Malvaceae family (3 species), and Convolvulaceae family (2 species). A terrestrial plant species, Calotropis gigantea was dominant in North Coromandel coast, abundant in South Coromandel coast and co-abundant in Palk Bay and Gulf of Mannar. Two mangrove associates Pongamia pinnata and Ipomoea pes-caprae were dominantin North Coromandel coast were observed as dominant species. Three associate species in Pongamia pinnata and Calotropis gigantea in South Coromandel coast and Citrullus colocynthis in North Coromandel coast were found as abundant - species (Table 3 & Figure 1).
Figure 1 Occurrence and distribution of mangroves and associates in Tamil Nadu estuaries during 2012-2014
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Mangrove associate plants were mostly found in all the sampling stations, but mangrove plants were noted only in a few stations. A mangrove species (Avicennia marina) and four associates (Thespesia populnea, Sesuvium portulacastrum, Calotropis gigantea and Citrullus colocynthis) were reported in all five groups of study areas. Three mangrove species (Avicennia officinalis, Rhizophora apiculata and R. mucronata) and nine associates (Catharanthus roses, Pongamia pinnata, Suaeda maritima, S. monoica, Salicornia brachiata, Clerodendrum inerme, Ipomoea pes-caprae, Cressa cretica, Spinifex littoreus, Casuarina equisetifolia) were present in four groups of study areas (Table 2 & 3).
Mangroves and its associates were more in Vellar (23 species), Coleroon (17 species), Manakkudy (14 species), Sethukarai (12 species), Punnaikayal (11 species) and Palayakayal (11 species). Two stations (Kallimedu, Arichandra nadhi) mangrove and its associates were totally absent. Less number of mangrove and its associates were reported in Nandalar (1 species), Thengapattinam (3 species), Thiruchendur (3 species), Valinokkam (3 species), Sundra Pandia Pattinam (3 species), Thiruchendur (3 species), Pattankadu Pattankadu (3 species), Mallipattinam (3 species), Rajamadam (3 species), Thirumalairajan aru (3 species), Cauvery-Poompuhar (3 species), and Kadilam (3 species). In the West coast of Tamil Nadu, Manakkudy have recorded more number of species (14 species) and less number of species (3 species) in Thengapattinam. In Gulf of Mannar more number of mangrove and its associates in Mannapadu (12 species), Punnaikayal (11 species), Palayakayal (11 species) and less number of species (3) in Thiruchendur and Valinokkam. In Palk Bay more numbe of species (7 species) was reported in Semangkottai and R. Pudupattinam and less number of species (3 species) in Sundra Pandia Pattinam, Pattankadu, Mallipattinam and Rajamadam. In South Coromandel Coast more number of species (10 species) was recorded in Mullai aru, Uppanar and Arasalar and less number of spcies (1 species) in Cauvery-Poompuhar. In North Coromandel Coast more number of species were reported in Vellar (23 species) during summer and less number species were recorded in Kadilam (3 species), Alampara kottai (4 species), Koovathur (4 species) and Cooum (4 species) (Figure 1).
Discussion
Chapman3 recorded 90 species, Saenger et al26 83 species, UNDP/UNESCO27 65 species and Tomlinson10 reported 46 species. In Eastern Australia, 27 species of mangroves have been recorded by Jones28 55 species by Walsh29 and 45 species by Bunt et al30. Total of mangrove species in difference countries (Indonesia 45 species; Malaysia 40 species; India 39 species; Thailand 34 species; Singapore 31 species; Myanmar 28 species; Bangladesh 24 species; Sri Lanka 23 species; Maldives 13 species; Mozambique 9 species; Tanzani 9 species; Kenya 9 species; Madagascar 9 species; Seychelles 8 species; Pakistan 8 species; Mauritius 3 species) recorded31. In India, 39 mangroves under 19 genera and 14 families along with 86 mangrove associates under 73 genera and 44 families have been reported31, 82 species of mangroves have been found distributed in 52 genera and 36 families32 and 50-60 species are recorded by Blasco6. Untawale33 has recorded 33 mangrove species from West coast, and 60 species from Ganges, Brahmaputra, Mahanadi, Godhavari, Krishna and Cauvery. From Sundarbans, 36 species have been reported34. A comparative analysis of the list of mangrove species was given by Untawale35, Banerjee & Rao36, Deshmukh & Mahalingam37, Chaudhuri & Choudhury38, Satyanarayana et al39 and Ramasubramanian et al40, which indicates a total number of 34 true mangrove species in the mangroves of India, including both east and west coasts and Andaman and Nicobar islands. Kathiresan18 has recorded 36 species of mangroves under 19 genera and 14 families in east coast of India, while 25 species of mangroves under 14 genera and 9 families in west coast of India, and 36 species under 18 genera 14 families in Andaman and Nicobar Islands18. Highest mangrove species were reported in Odisha (101 species), followed by Sundarbans (92 species) and Andaman & Nicobar (91 species), whereas Gujarat is represented with lowest diversity of 36 species18. The mangrove wetlands of Orissa has 31 species36, while Sundarbans of West Bengal has 24 species, similar to Andaman and Nicobar Islands38. Nine true mangrove species and ten associates have been identified in Kundapura area of Karnataka41. Mangroves in Tamil Nadu have been recorded with different number of species:14 species37,40, 16 species31. In Pichavaram area of Tamil Nadu is recorded with 13 true mangrove tree species and 73 other vegetation42. The present study registered 16 mangroves and 23 mangrove associates along the 56 estuaries of Tamil Nadu coast (Table 1 & 2).
Table 1 Name of estuaries in the collections sites of five divisions
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Table 2 Occurrence and distribution of mangroves species in 56 estuaries of Tamil Nadu during 2012-2014
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Table 3 Occurrence and distribution of Mangrove Associates in 56 estuaries of Tamil Nadu during 2012–2014
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Table 4 Occurrence and distribution of Mangroves and associates in 56 estuaries of Tamil Nadu
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Families such as, Plumbaginaceae, Avicenniaceae, Arecaceae and Pellicieraceae contain only mangrove species. Two orders Myrtales and Rhizophorales contain 25% of all mangrove families. In the present study 40% of mangroves species from Rhizophoraceae family and 20% species in Avicenniaceae family were reported (Table 1 & Figure 2), while 20% of mangrove associate species were reported in Chenopodiaceae family and 12% of species in Malvaceae family (Table 2 & Figure 1). Mangrove species such as Pemphis acidula is endemic to island of Gulf of Mannar of Tamil Nadu. Scyphiphora hydrophyllacea is restricted to Godavari mangroves of Andhra Pradesh, while Nypa fruticans is present only Sundarbans of West Bengal and Andaman and Nicobar Islands31. Xylocarpus species are reportedly restricted to Andaman and Nicobar Islands, Sundarbans, Mahanadi delta, Andhra Pradesh and Pichavaram43-47. Similarly, during the present study a mangrove species (Bruguiera gymnorrhiza) was noted only in Ariyankuppam and Thengaithittu estuary of North Coromandel coast and Avicennia alba from Palayakayal estuary of Gulf of Mannar region (Table 1) and two mangrove associates (Acrostrichum aureum and Fimbristylis ferruginea) were reported in the Manakkudy estuary (Table 2).
Figure 2 shows the collection sites of estuaries of Tamil Nadu
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Acknowledgement
We are thankful to the authorities of Annamalai University for providing facilities and to the University Grants Commission (UGC), New Delhi for financial support under CPEPA programme.
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