The Gulf of Mannar Marine National Park is a protected area of India consisting of 21 small islands and adjacent coral reefs in the Gulf of Mannar in the Indian Ocean. It lies 1 to 10 km away from the east coast of Tamil Nadu, South India for 160 km between Thoothukudi and Dhanushkodi. It is the core area of the Gulf of Mannar Biosphere Reserve which includes a 10 km buffer zone around the park, including the populated coastal area. The park has a high diversity of plants and animals in its marine, intertidal and near shore habitats. Public access inside the Park is limited to glass bottom boat rides
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 (23%) 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 belonging to the family Chaetodontidae, (butterfly fish); Parrotfish; Amphiprion spp (clown fish), Holocentrus spp (squirrel fish), Scarus spp (parrot fish), Lutjanus spp (snappers) and Abudefduf saxatilis (sergeant Major) are abundant.
A unique endemic species of Balanoglossus – Ptychodera fluva, a living fossil that links invertebrates and vertebrates, has been recorded only at Kurusadai.