139736eo.pdf (20MB) - Japan Oceanographic Data Center

INDIAThe coral reef formations in India are restricted to the atolls of the Laccadive Archipelago, andto the fringing and patchy reefs located in the Gulf of Kutch along the northwestern coast, the PalkBay and Gulf of Mannar on the southeastern coast and the Andaman and Nicobar islands in the Bay ofBengal. SEWELL (1932) related the absence of coral reefs from a major part of the Bay of Bengal andthe subcontinental coasts of India to the large influx of freshwater and silt from the major rivers of thearea. Further, SEWELL (1935) suggested that the presence of high levels of nitric acid in the GangesRiver, especially during the monsoon season, could discourage the growth of corals in the Bay ofBengal. More recently, PILLAI (1967, 1969a, 1969b, 1971a, 1971b, 1971c, 1972) made a valuablecontribution to the knowledge of corals around India; there appears to be no work on the Scleractiniafrom the Gulf of Kutch" (PILLAI, 1971a).MAHADEVAN and NAYAR (1972), as well as VENKATARAMANUJAM et al. (1981),discussed the exploitation and utilization of corals in the Gulf of Mannar and Palk Bay for making limeas building material and for road construction. RAJENDRAN and DAVID (1972) estimated the extentof coral reefs in and around some of the islands in the Gulf of Mannar, while MERGNER andSCHEER (1974) described the physiographic zonation and ecological conditions of some coral reefs insouthern India.Gulf of Mannar and Palk BayThe coral reefs of this area are of the fringing or patchy type, thriving in shallow waters eithernear the shores of the mainland or encircling a few islands. PILLAI (1971a), referring to the reefs ofthe area, stated that " ...shallow waters with muddy or sandy surroundings considerably restrict thegrowth of corals and at present the reefs seem to be in a state of deterioration".Running almost parallel to the coast of South India in the Gulf Mannar are 21 islands oflimited extent lying between 8'47'N - 9'15'N latitude and 78'12'E - 79'14'E longitude. Many ofthese islands have well-developed fringing reefs of varying sizes located 100 to 150 m from theshoreline. In addition to these islands, coral reefs occur around Rameswaram Island, the largest islandin this group. One reef starts from north-northeast shore of Rameswaram, runs around Devil's Pointparallel to the shore and extends up to Mandapam in the Palk Bay (MAHADEVAN and NAYAR,1972). This reef, which is located 300-600 m offshore, has a 1-2 m deep (at low tide) sandy lagoonwhich is generally devoid of any coral (PILLAI, 1971a). Most of the recent investigations on the coralreefs of Palk Bay and Gulf of Mannar have been carried out on these reefs.PILLAI (1972) recorded 110 hermatypic coral species belonging to 25 genera and 7ahermatypic corals belonging to 7 genera from Mandapam area. From Tuticorin in the Gulf ofMannar, he recorded 16 hermatypic coral species belonging to 14 genera. All these species have beencollected from shallow waters not deeper than 2 m at low tide. The deeper waters are yet to beinvestigated.The Gulf of Mannar appears to be a unique zone with regard to the variety of fishing activities.MAHADEVAN and NAYAR (1972) stated that ".. . the nature of the sea-bottom in the inshore area ofthis zone supports certain fishing occupations which are not met within most other zones of the Indiancoast. These are the chank fishing, pearl oyster fishing and coral quarrying. The fishermen find asteady income in bringing coral stones or coral blocks broken by them from the shallow areasadjoining many small islands between Tuticorin in the south and Pamban at the head of the Gulf '. TheGulf fishermen also exploit the coral reefs from Palk Bay. Of the many coral species that occur in thearea, only a few species such as Acropora formosa, Porites compressa, P. solida, P. somaliensis,Favia vdenciennesii and Tubjpora spp. are exploited for commercial purposes (PILLAI, 1967:. A.formosa fragments, popularly called 'challi', are collected extensively for manufacturing lime, whileother corals such as the massive Porites sp. and Favia valenciennesii are collected for other purposes.VENKATARAMANUJAM et al. (1981) estimated that at Tuticorin alone some 30,000 cubic meters(approximately 15,000 tons) of coral stones are landed every year. PILLAI (1971a) indicated thatcoral quarrying has resulted in large scale destruction of these reefs and their associated fauna. Hestated further, that ".. . some of the islands in the Gulf of Mannar are almost completely exploited,157