The Gulf of Mannar ( ) is a large shallow bay forming part of the Laccadive Sea in the Indian Ocean with an average depth of . It lies between the southeastern tip of India and the west coast of Sri Lanka, in the Coromandel Coast region. The chain of low islands and reefs known as Ram Sethu (aka Adam's Bridge), which includes Mannar Island, separates the Gulf of Mannar from Palk Bay, which lies to the north between India and Sri Lanka. The estuaries of Thamirabarani River and Vaippar River of South India and the Malvathu Oya (Malvathu River) of Sri Lanka drain into the Gulf. The dugong (sea cow) is found here. Conservation Marine sanctuary Located on the southeastern tip of the subcontinent, the Gulf of Mannar is known to harbour over 3,600 species of flora and fauna, making it one of the richest coastal regions in Asia. Around 117 hard coral species have been recorded in the Gulf of Mannar. Sea turtles are frequent visitors to the gulf as are sharks, dugongs, and dolphins. However, the combined effects of 47 villages, with a total population of around 50,000 has meant that overharvesting of marine species has become a problem. The decline of fish populations has been accompanied with reducing numbers of pearl oyster, gorgonian coral, and acorn worm. Local fishermen rely on the reef to feed their families, but destructive fishing methods combined with the stress of pollution and coral mining have meant both nearshore and offshore catches have decreased. Endangered species include dolphins, dugongs, whales and sea cucumbers. In 1986, a group of 21 islets lying off the Tamil Nadu coast between Thoothukudi and Dhanushkodi was declared the Gulf of Mannar Marine National Park. The park and its 10 km buffer zone were declared a Biosphere Reserve in 1989. Biosphere reserve The Gulf of Mannar Biosphere Reserve covers an area of 10,500 km2 of ocean, 21 islands and the adjoining coastline. The islets and coastal buffer zone include beaches, estuaries, and tropical dry broadleaf forests, while the marine environments include seaweed communities, sea grass communities, coral reefs, salt marshes and mangrove forests. In May 2019, The National Centre for Coastal Research, an institute under the Ministry of Earth Sciences of India, which has a field research station in the Gulf of Mannar region, found an alarming pattern of bleaching in the reefs in Mandapam, Kilakarai and