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| Last Updated:: 01/09/2023


Coastal environment plays a vital role in nation's economy by virtue of the resources, productive habitats and rich biodiversity. India has a coastline of about 7,500 kms. The coastline of Tamil Nadu has a length of about 1076 kms constitutes about 15% of the total coastal length of India and stretches along  the Bay of Bengal, Indian Ocean and Arabian Sea. Tamil Nadu is one of the 29 states of India.  It is situated at the South Eastern extremity of the Indian Peninsula bounded on the north by Karnataka and Andhra Pradesh, on the east by Bay of Bengal, on the South by the Indian Ocean and on the West by Kerala. It has one of the longest coastlines in India with 13 coastal districts.
The coast of Tamil Nadu has three major ports, seven Government captive ports, and 16 non major ports, fishing harbors and a variety of coastal industries like nuclear and thermal power plants, refineries, fertilizers etc. The coast is also endowed with varied coastal habitats like mangroves, corals, seaweeds, sea grass beds, salt marshes, mudflats, sand dunes etc. The State also has a number of rivers, estuaries and lagoons. The rivers flow west to east towards the Bay of Bengal. Some of the important rivers are Cauvery, Vaigai, Tamiraparani, and Pennar. The River Cauvery forms the major estuary in Tamil Nadu and the minor estuaries include Vellar, Pazhayar, Adyar etc. The lagoons are Pulicat lake (South) and Muthupettai.
 The coastal areas are assuming greater importance, owing to increasing human population, urbanization and accelerated developmental activities. The coastal ecosystems are now highly disturbed and very much threatened, encountering problems like pollution, siltation and erosion, flooding, saltwater intrusion, storm surges and other activities due to ever expanding human settlements. These anthropogenic activities have put tremendous pressure on the fragile coastal environment. Tamil Nadu coast has been blessed with vital eco-systems and preservation and protection of the eco-system is vital for sustainable development.  
 Coastal length of Tamil Nadu
 Sl. No
Coastal Districts
Coastal length in km
Coastal Biodiversity in Tamil Nadu  
The marine biodiversity of Tamil Nadu is rich and varied. The coastline encompasses almost all types of intertidal habitats from hyper saline and brackish water lagoons, estuaries and coastal marsh and mud flats to sandy and rocky shores with varying degrees of exposure and widely varying profiles. Subtidal habitats are equally diverse.
Each local habitat reflects prevailing environmental factors and is further characterized by its biota. Thus the marine fauna itself demonstrates gradients of change throughout the Tamil Nadu coast. Among coastal wetlands, estuaries, mangroves and coastal lagoons are biodiversity rich areas, whereas the other brackish water habitats have only a few specialized species. It is well known that the reduction in number of species is greater in estuaries when compared to adjacent seas and in-flowing river systems.
It has been observed that as the distance increases from the sea, the number of species decreases. Salinity becomes the important regulating factor. However, much study is to be conducted in the estuaries, mangroves and coastal lagoons of Tamilnadu. 
Corals and coral reef associated organisms 
            Coral reefs are one of the important ecosystems in India. They form the most productive, dynamic ecosystem providing shelter and nourishment to thousands of marine flora and fauna. They are the protectors of the coastlines of the maritime states. They are well developed in warm, clear, shallow coastal regions where light is abundant.
Massive deposits of calcium carbonate that are secreted by the corals form the main girdle of the reef. Corals growth is greatly influenced by the presence of an algae called “Zooxanthellae” that provides a symbiotic relationship with the corals. The interaction of coral reefs with algae provides habitats for all the other reef associated organisms.
They protect shorelines from erosion and damage due to cyclone. The sand beaches around these coral reefs are also used as tourist spots which earns foreign exchange. These coral reefs are also called as marine biodiversity supporting many species of corals, fishes, crustaceans and many other animals and plants. Coral reefs are often termed as fragile ecosystems.
 If the present day human population does not coexist well with the coral reef ecosystem, there will be a decline in the coral reef biodiversity. The total area of coral reef in India is estimated to be 2,374.9 km2. In Tamil Nadu, the area estimate of coral reefs is represented in the Table.
  Estimates of Coral Reef in Tamil Nadu



 Category Tamil Nadu



Reef flat



Sand over reef



Reef vegetation



Vegetation over sand











In TamilNadu, the coral reefs are distributed along the Gulf of Mannar, Palk Bay and at restricted places in Chennai, Pondicherry and Cuddalore. The reef formation of southeast coast of India along the Tamilnadu coast is scattered between 79° to 79°9’E to 8°45’ to 9°11’N covering nearly 21 islands from Tuticorin to Rameswaram.
Though the reefs are mostly of fringing types around the islands, it is discontinuous barrier, termed as ‘Mannar Barrier’. The fringing reefs around the islands normally have a lagoon of 100-150 m wide and 1-2 m deep. The dominant genera include Acropora, Montipora and Pocillopora among the ramose forms.
Massive forms are represented by Porites, Favia, Favites,Goniastrea, Platygyra and rarely SymphylliaCyphastrea and Leptastrea are very common on all reef habitats of this area. The foliaceous forms are Echinoptera, Lamellosa and Montipora foliosa in Gulf of Mannar. In Palk Bay, the reef extends along the shore from Mandapam eastward along the shores of Rameswaram island interrupted only at Pamban pass.
Corals are found on reef rocks and no consolidated reef flat is seen. Zonation is indistinct. The siltation especially during monsoon along the inshore region is reported to have marked impact on the distribution of corals on the reef.
Mangroves in Tamil Nadu 
  • Mangroves are of great ecological and economic significance and are among the most productive ecosystems. 
  • Because their high rate of production of organic matter, the mangrove are able to sustain a diverse community of organisms, ranging from bacteria to fishes, birds and mammals. 
  • Tamilnadu has two major mangrove forests. 
  • The Pichavaram mangrove is located 200km south of Chennai covering an area of 1,100 ha. The whole mangroves consist of 51 small and large islands and are bathed with seawater during high tide and freshwater from irrigation channels during low tide. 
  • The Muthupet mangrove forest which spreads over an area of approximately 6,800 ha. of which only 77.2 ha. (4%) is occupied by well grown mangrove and the remaining 96% of the area is covered by poorly grown mangrove vegetation, situated near Point Calimere on the southeast coast of the peninsular India.
  • The Pichavaram and Muthupet mangrove ecosystems embrace a heterogeneous mixture of plants and animals. 
  • The aquatic fauna comprises of juveniles and adults of finfishes, shrimps, mollusks, crabs and benthic invertebrates. About 13 species of true mangrove species are present in Pichavaram. 
  • The Rhizophora annamalayana has been described as a hybrid between Rhizophora stylosa and Rhizophora apiculata.
  • The distribution of various species of mangroves in Shingle, Krusadai, Poomarichan, Manoliputti, Manoli, Musal (Hare), Mulli, Poovarasanpatti, Anaipar, Upputhanni,Kasuwar, Valai, Appa, Nallathanni, Karaichalli, Van Tivu, Thalaiyari, Vallimunai, Puluvunnichalli and Vilanguchalli islands of Gulf of Mannar revealed dominant species of Avicennia marina, Rhizophora mucronata, Bruguiera cylindrica, Ceriops decandrus, Lumnitzera racemosa, Exoecaria agallocha and Suaeda spp. 
  • The Pichavaram mangroves are an important breeding and nursery area for many fishes, crustaceans and the waterfowl population. 
  Sea grass and seaweeds in Tamil Nadu:
         Sea grasses occur in the intertidal and midtidal zones of shallow and sheltered areas of sea, gulf, bays, backwaters and lagoons. They are submerged monocotyledonous plants and are adapted to the marine environment for the completion of their life cycle under water. They form a dense meadow on sandy and coral rubble bottom and sometimes in the crevices under water.
Sea grasses are involved in cycling of nutrients. They provide food, shelter for diverse organisms and act as a nursery ground for many fishes of commercial importance and play a vital role in the fisheries production of the region.
Among the 6 Indian genera of sea grasses, 11 species are recorded from Palk Bay of Tamil Nadu. Of the 11 species, Cymodocea serrulataHalophila ovalisHalodule pinifolia and Syringodium isoetifolium are predominantly distributed. Halodule wrightii occur only in Akkalmadam in Rameswaram. 13 species of seagrasses under 6 genera occur in the Gulf of Mannar region.
Enhalus acaroides, Halophila ovalis, Halophila ovata, Halophila beccari, Halophilastipulacea, Thalassia hemprichii, Cymodocea serrulata, Cymodocea rotundata, Halodule uninervis, Syringodium isoetifolium are some of the seagrasses available inthe Gulf. Thalassia and Syringodium are dominant in the areas of coral reefs and coralrubbles whereas others are distributed in muddy and sandy soils. The uniqueecological importance of the sea grasses is the conservation of rare and endangeredanimals like marine turtles, dugongs and some echinoderms.
 Seaweeds are marine plants belonging to lower Cryptogams. They are one of the commercially important marine living renewable resources. They occur in the intertidal, shallow and deep waters of the sea up to 150 m depth and also in estuaries and backwaters.
These are large and diversified groups with size ranging from single cell such as Chlamydomonas to several meters in length (Macrocystis). The four classes of seaweeds are Chlorophyta (green algae), Phaeophyta (brown algae), Rhodophyta (red algae) and Cyanophyta (blue-green algae).
In India, so far 650 species of marine algae with a maximum of 320 species of Rhodophyta followed by 165 species of Chlorophyta and 150 species of Phaeophyta have been recorded. Out of these, Tamilnadu has the maximum (302 species).
A total number of 147 species of algae comprising 42 species of green algae, 31 species of brown algae, 69 species of red algae and 5 species of blue green algae distributed in Gulf of Mannar islands. The agar yielding seaweeds are being harvested since 1966 from Gulf of Mannar islands, along the coastline from Rameswaram to Tuticorin and Sethubavachatram area in Palk Bay.
The following economically important species were recorded in Gulf of Mannar islands. Gelidiella acerosa, Gracilaria edulis, G.follifera, Gracilaria sp., Hypnea sp. Acanthophora,Sargassum sp., Turbinaria sp., Cystoseira trinodis and Hormophysa triquetraUlva sp., Enteromorpha, Caulerpa, Codium, Hydroclathrus, Halimeda, Padina, Chondrococcus and Laurencia
Gulf of Mannar Biosphere Reserve (GoMBR): 
The Gulf of Mannar in the southeast coast of India extends from Rameswaram in the north to Kanyakumari in the south. It has a chain of 21 uninhabited islands stretching from Pamban to Tuticorin to a distance of about 140 km along the coast. The islands occur at an average distance of 8-10 km from the mainland.
The Government of Tamil Nadu in 1986 declared the 21 islands and surrounding shallow coastal waters as Marine National Park for the purpose of protecting marine wildlife and its environment. The Gulf of Mannar Biosphere Reserve was set up in 1989 by Government of India covering 10,500 area between Rameshwaram and Kanniyakumari. 
 The Gulf of Mannar is endowed with rich biodiversity as it includes diverse nature of ecosystems like coral reefs, rocky shores, sandy beaches, mud flats, estuaries, mangrove forests, and seaweed and sea grass beds. It was once considered as “Biologists’ paradise” for its rich biological treasure with over 4200 species of flora and fauna.
 The coral mining until 2005, destructive fishing practices like inshore trawling, shore seine operation and trap fishing, seaweed collection, industrial and domestic pollution, bio-invasion and developmental activities caused severe damage to key habitats like coral reefs and sea grass beds, resulting unstable substratum and loss of biodiversity. About 32 reef area and over 22 sea grass bed area have been degraded in Gulf of Mannar.
Different types of reef formation have been observed in Gulf of Mannar i.e. fringing reef, patchy reef and coral pinnacles. The major coral genera include Acropora, Pocillopora, Montipoora, Turbinaria, Echinopora, Favia, Favites, Goniastrea, Leptastrea, Leptoria, Platygyra, Goniopora, Porites, Merulina, Symphyllia, Galaxea, pavona, Coscinaria, Psammacora etc.
 Mangroves are salt tolerant forest ecosystems, which support fisheries and protect the coastal zones, thus helping the marine coastal economy and environment. They are ecologically sensitive. 9 species and 7 associated species were found in Gulf of Mannar.
 The roots of mangrove plants have the unique habit of moving towards gravity. The leaf litter from plants, fall on the sea water nourish the water and increase its nutrient content. This excess nutrient is food for fish fry that hatch there. Some of these plants have medicinal value.
 Government has taken several initiatives to restore and conserve the island ecosystem and its biodiversity through various rehabilitation programmes. Several rehabilitation works are being implemented by various Government departments like Tamil Nadu Forest Department, Department of Environment, and GoMBRT etc.,
 Through SDMRI which has taken up such research activities since 2002 and also standardized the low-tech and low-cost methods. Coral rehabilitation in 2 degraded reef area was done in four islands by Tamil Nadu Forest Department (TNFD) during 2008-09; in 1 degraded area in two islands by Gulf of Mannar Biosphere Reserve Trust (GOMBRT) during 2008; 1 area in one island during 2012-13 by GIZ and Tamil Nadu Environment Department (TNED); and 2 area in two islands by TNFD during 2013-14
 Sea grass rehabilitation was done in 1 degraded area in one island by GIZ and TNED during 2012-13 and 1 area in Tuticorin coast by IUCN during 2014 (A pilot scale artificial reef programme was implemented near Vaan Island in April 2014 by GOMBRT through SDMRI not only to protect the island from erosion but also to increase the biodiversity, in particular the fishery production.
 The intervention in the form of coral rehabilitation along with other conservation initiatives by the Tamil Nadu Forest department involving SDMRI resulted in the increase in live coral cover about 6%. The vast coral recruitment over 20% degraded reef area helped in healthy coral reef cover along with associated biodiversity.
 Government has also implemented programmes to build capacity among frontline forest staff to protect the island resources. Several officials and field staff from Forest Department have been trained in SCUBA diving to assess and monitor the coral reef and sea grass areas and also help to protect the resources. 
Ramesh R., Nammalwar P.and. Gowri V. S., 2008. The Database on Coastal Information Of Tamilnadu, Environmental Information System (ENVIS) Centre Department Of Environment, Government Of Tamilnadu Chennai. Tamil Nadu Forest Department .