The park is part of the 140 km long and 25 km wide Mannar barrier reef. It lies between 8° 47' to 9° 15' N latitude and 78° 12' to 79° 14' E longitude. The 21 islands vary from 0.25 ha to 130 ha.. Total area of the islands is The islands Tuticorin group: Vaan, 16.0 ha Koswari, 19.50 ha Vilanguchalli, 0.95 ha, now 1 m below mean low tide level as a result of excessive coral mining. Kariyachalli, 16.46 ha Vembar group:
Uppu Thanni, 22.94 ha, elevation 4 m
Puluvini Challi, 6.12 ha, elevation 5.5 m
Nalla Thanni, 101.00 ha, elevation 11.9 m Kilakarai group:
Kurusadai, 65.80 ha was recently populated. Its surrounding shallow waters harbour three species of seagrass that are found nowhere else in India. Representatives of every animal phylum known are found on this island.
Shingle, 12.69 ha, elevation.6m Tidal amplitude in the area is about.5m. There were two more islands named Pandayan and Punnaiyadi at that were destroyed for construction of the new Tuticorn Port facilities.
Flora and fauna
The park includes estuaries, mudflats, beaches and forests of the near shore environment. It also includes marine components such as coral reefs, seaweed communities, sea grasses, salt marshes and mangroves. Flora – Mangroves dominate the intertidal zones of the park islands. They consist of species of the genera Rhizophora, Avicennia, Bruguiera, Ceriops and Lumnitzera. Mangroves: . The introduced tree genus Prosopis is dominant on land in all the islands. The flowering herb Pemphis acidula is the only endemic plant species. 12 species of sea grass and 147 species of seaweeds were recorded. This vegetation provides important feeding grounds for the vulnerablemarine mammal, the dugong, endangeredgreen turtles and vulnerable olive ridley turtles. Sea grasses: Fauna Vertebrates The dugong, a vulnerable marine mammal, is the flagship mammal of the park. It is an important habitat for the cetaceans: Indo-Pacific bottlenose dolphin, finless porpoise, spinner dolphin, common dolphin, Risso's dolphin, melon-headed whale, and dwarf sperm whale. Larger whales include sperm whale, minke whale, Bryde's whale, sei whale, and critically endangered species including humpback whale, fin whale, and blue whale. About 510 of the 2,200 fin fish species in Indian waters are found in the Gulf, making it the most highly diverse fish habitat in India. Coral associated ornamental fishes of the family Chaetodontidae, parrotfish, Amphiprion spp., Holocentrus spp., Scarus spp., Lutjanus spp. and Abudefduf saxatilis are abundant. A unique endemic species of Balanoglossus – Ptychodera fluva, a living fossil that links invertebrates and vertebrates, has been recorded only at Kurusadai. Invertebrates Four species each of shrimp and lobster, 106 species of crab, 17 species of sea cucumber, and 466 species of mollusc including 271 gastropods, 174 bivalves, 5 polyplacophorans, 16 cephalopods and 5 scaphopods, 108 species of sponge, and 100 species of echinoderm occur in the Gulf. The coral fauna includes 106 species from 30 genus of hermatypes and 11 species from 10 genus of ahermatypes, including 13 new species, giving a total of 117 species from 14 families and 40 genus. The reefs in this area are narrow fringing reefs located 150 to 300 m. from the shore of the islands and patch reefs rising up from depths of 2 to 9 m. and extending up to 2 km. long and 50 m. wide. Large areas of these reefs are in generally poor condition due to destructive human activities of the 150,000 persons living along the coast. Nutrient and other pollution loads are high due to agriculture, deforestation, industry, urbanization and septic pollution. It appears that the coral reefs of the Gulf of Mannar Marine National Park seem to be healthy and in good condition, despite high rates of sedimentation and other threats. However, live coral cover is only about 35%. Various algae cover much of the dead coral. Stony coral species of families Poritidae and Faviidae constitute the dominant reef builders here. Coral reefs near some of the islands have been heavily damaged by exploitation as raw materials for industrial ventures such as cement industries, brick manufacture, masonry work and lime kilns. Though legal quarrying of the reefs is now stopped, up to 250 m3/day of reef were destroyed for many years.
Habitation
The islands are uninhabited except for Krusadai, Musal and Nallathanni islands where antipoaching sheds are operating. Along the coast near the park there are about 125 villages which support about 100,000 people who are mainly Marakeyars, a local community principally engaged in fishing.
Habitat Degradation
Experts say that Vaan Island, one of the four islands of the Tuticorn group, has split in two and if immediate efforts are not taken then the island would soon vanish under the sea. Vaan Island, which is the southernmost of the 21 islands in the Gulf of Mannar, was initially spread across 16 hectares, but had shrunk alarmingly by around 10.3 hectares to its current 5.7 hectares in less than three decades. According to J K Patterson Edward, director of Suganthi Devadasan Marine Research Institute, Tuticorin,"Rampant coral mining by people of the fishing villages along the coast is the main cause of the devastation to the island. Coral mining was banned in 2005, but the damage had already been done." Two of the 21 islands have already submerged around a decade ago.
Visitor information
Glass-bottomed boats available at Mandapam cater to tourists visiting the area. Access to the islands is prohibited. The nearest railway stations are at Mandapam and Tuticorin.
