Water temperature is rather constant through the year, averaging 26–28 °C in summer and 25 °C in winter. Salinity is 34‰ (parts per thousand) in the center and northern part and up to 35.5‰ in the south. The coasts are sandy and the deeper parts covered insilt. There are numerouscoral reefs in the sea, such as theLakshadweep islands which are made up ofatolls and contain 105 coral species.[1][4][5]
TheGulf of Mannar is known for itspearl banks ofPinctada radiata andPinctada fucata for at least two thousand years.Pliny the Elder (23–79) praised thepearl fishery of the gulf as the most productive in the world.[6][7] Although extraction of natural pearls is considered too expensive in most parts of the world, it is still conducted in the gulf.[8][9] Also collected in large numbers areShankha mollusks (Xancus pyrum)[8] whose shells are used as aritual and religious object. Other mollusks of the sea[10] are either too scarce or not popular in Indian society and therefore have no commercial value.[11]
Another traditional occupation in the Laccadive Sea is fishing. The annual fish catch is 2,000 to 5,000 tonnes from the Lakshadweep islands, which is mostly constituted by tuna (about 70%) and shark.Perches,halfbeaks,Carangidae,needlefish and rays are also caught near the reefs.Shrimp,Achelata[1] and small fish, such asSprattus,Pomacentridae andApogonidae are widely used as a bait by the Laccadive islanders.[12]
With about 3,600 species of flora and fauna, the Gulf of Mannar is regarded as one of the richestmarine biological resources in the world. Of these 3,600 species, 44 are protected, 117 are corals, 79 crustaceans, 108 sponges, 260 mollusks, 441 fin fishes, 147 seaweeds and 17 mangroves.[13] In 1986, a group of 21 islands and nearby waters with a total area of 560 km2 were declared as theGulf of Mannar Marine National Park. The park and its buffer zone were designated as aBiosphere Reserve in 1989. TheGulf of Mannar Biosphere Reserve covers an area of 10,500 km2 of ocean, islands and the adjoining coastline, and is the largest such reserve in India. Most of its area is restricted for outsiders and the access of boats is subject to strict rules,[14] but local people continue fishing activities which they crucially depend on. About 150,000 people live in the buffer zone, and more than 70% of them depend on the coastal marine resources. There are about 125 fishing villages with 35,000 active fishers and 25,000 divers forsea cucumbers in the area, about 5,000 women collect seaweed.[15][16] About 106,000 tonnes of fish were produced in the gulf in 2006, mostlyoil sardines (Sardinella longiceps), lessersardines(Sardinella spp.),ponyfish (Letognathus sp.),mackerel,penaeid shrimp,perches,squid (Sepioteuthis arctipinni), deep-sealobster (Puerulus sewelli),crab (Varuna littorata),skates andsting rays.[11][17] The seaweed collection aims at shallow-water speciesGelidiella acerosa (marikozhundu passi),Gracilaria edulis (Agarophytes,Kanchi passi),Sargassum spp. (kattakorai),Turbinaria (Alginophyte,Pakoda passi) andUlva lactuca, and is conducted between October and March. Because of National Park related restrictions, the production of seaweeds declined from 5,800 tonnes (dry weight) in 1978 to 3,250 tonnes in 2003.[18]
