Molluscs (oysters and clams): The diversity of molluscs from various parts of the world varies from 80,000 to 1,50,000. In India, malacological studies began in the early-20th century. The ZSI, Central Marine Fisheries Research Institute (CMFRI) and several maritime universities have contributed immensely to the knowledge of molluscan fauna. In India, 5100 species of molluscs have been discovered from freshwater (183 species), land (1487) and from marine habitats (3400) (Subba Rao, 1991, 1998 and 2000).
The Andaman and Nicobar have the richest molluscan diversity, with over 1000 species. The Gulf of Mannar and Lakshadweep have 428 species and 424 species respectively (ZSI, 2004). Eight species of oysters, two species of mussels, 17 species of clams, six species of pearl oysters, four species of giant clams, one species of window-pane oyster and other gastropods such as Sacred chank, Trochus, Turbo as well as 15 species of cephalopods are exploited heavily in the Indian seas.
Sea slugs (opisthobranchs) are shell less molluscs which are colourful and mostly found on Indian coral reefs. There are 388 species of sea slugs in India, 200 of which are found in the coral reefs of Andaman and Nicobar Islands alone.
A significant dietary component for the poor in coastal India, shell fish are an important raw material for mother-of-pearl and shell lime pottery glazes, besides jewellery and decorative art work. Shellfish are also used as a poultry feed additive, while the shells of certain species like Villorita cyprinoides and V. cornucopia are used as raw material in the cement and rayon industry. However, over exploitation of molluscs can affect ecosystems, since molluscs play an important role in the formation of organic detritus in estuaries.
Holothurians (sea cucumbers and starfish): So far, 777 species of sea cucumbers and starfish have been recorded, of which 300 species are from the Andaman and Nicobar (Sastry, 1998; James, 1986). Of the rest, Lakshadweep has 77 species and the Gulf of Mannar, 112 species. Economically, only 12 species are known to be of commercial importance in India. Of these, only three species (Bohadschia marmorata, Holothuria scabra and H. spinifera) are exploited in the Gulf of Mannar. All holothurians are now included under Schedule 1 of the Wildlife Protection Act, 1972.
Marine reptiles (sea snakes, turtles and crocodiles): Thirty-three species of marine reptiles including 26 species of sea snakes, five species of sea turtles and one species of saltwater crocodile Crocodylus porosus have been documented in India. The first study on sea turtles in the coastal Indian waters was done by Smith (1931). Seven species of sea turtles are found in the world’s warm oceans, of which five are reported in India. The Leatherback sea turtle, Dermochelys coriaceais is a rare species. The remaining four namely the Green turtle (Chelonia mydas), the Olive Ridley (Lepidochelys olivacea), the Hawksbill (Eretmochelys imbricata), and the Loggerhead (Caretta caretta) belong to a single family, Cheloniidae. All of these nest on beaches throughout India. Nestlings are often preyed upon by wild animals, and badly affected by natural calamities. Commercial activities and the building of chemical factories, luxury resorts and theme parks along beaches can also destroy nesting sites.
In India, all five known species of sea turtles are fully protected from hunting, killing and other forms of exploitation under the Indian Wildlife (Protection) Act, 1972 since September, 1977.
Seabirds: The marine ecosystem offers a variable feeding and breeding ground for many seabirds. Although not spectacularly diverse, seabirds are a regular feature of marine and estuarine ecosystems. Some species are exclusively dependent on coral reefs, while a few are generalists without much dependence on the same. In the Andaman and Nicobar islands, pelagic seabirds notably boobies (Sulidae), shearwaters (Procellariidae) and terns (Sternidae), rarely ever nest, although waders and other seabirds are found on or near coral reefs. These include sandpipers, oystercatchers, turnstones and plovers. Egrets and herons are also widespread, often feeding across the reef flat at low tide.
In the Gulf of Kachchh, pelicans and flamingos abound. Birds of prey such as ospreys and sea eagles are also occasional visitors. In the Gulf of Kachchh Marine Park, 123 species of waterfowl and 85 species of terrestrial birds have been reported. Waders uncommon to India such as knot Calidrisca nuta, eastern knot Calidris tenuirostris, curlew Numenius auquata, Whimbrel Numenius phaeopus and bar tailed godwit Limosal apponica are regular winter visitors here (Balachandran, 1995).
Whales, dolphins and dugong: Marine mammals are classified under three major groups: Cetacea (whales, dolphins and porpoises); Sirenia (manatees and dugong); and Carnivora (sea otters, polar bears and pinnipeds). The Indian seas support 33 species of marine mammals, of which five are baleen whales. As per sighting records, the Indian seas are home to 20 cetacean species and one sirenian (ZSI, 2012).
The sea cow, Dugong dugon, lives in the near shore waters of the Gulf of Mannar, Gulf of Kachchh and the islands of Andaman and Nicobar. All reported marine mammals are protected under the Wildlife (Protection) Act, 1972, though information on their distribution remains scanty.
Protected Marine Animals: As per available data, India is home to 6.43 per cent of global marine biodiversity. Over 1180 species of marine fauna are protected under different categories (Schedule I, II, III, IV) of government legislation, since natural populations are all in diminishing mode.