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

Very little information is available on the utilization and cause of damage to the coral reefs inthe Central Indian Ocean. Other than the Hikkaduwa Marine Sanctuary on the southwestern coast ofSri Lanka, which was declared in 1979, and the recently declared Pirotan Island Marine Park in theGulf of Kutch in India, no other marine sanctuaries, reserves or parks exist in the Central IndianOcean. And even the Sri Lanka sanctuary has experienced difficulty in implementation of regulations,mainly because of socio-economic considerations. Currently, moves are underway to rectify some ofthe problems. ,The known distribution of the major coral reefs in the Central Indian Ocean are given in Figure1, and various areas are discussed in the following paragraphs.MALDIVE ISLANDSThe Maldive Archipelago, situated southwest of India, consists of 22 atolls (PILLAI andSCHEER, 1976) with about 1800 small islands, extending 764 km in a north-south direction. Thenorthern limit is Ihavandiffulu Atoll (7'05'N, 72"55'E), while Addu Atoll - one of the mostscientifically studied atolls - is located at the southern tip (0"40S, 73"lO'E). The atolls of Maldivesare distinguished by "faros" or small atoll-shaped reefs round their rims. Microatolls and patchreefs/knolls are also well documented in the Maldives. Although most of the Maldivian coral reefs areyet to be investigated, they are still the best-known coral reefs in the Central Indian Ocean.Investigations on the coral reefs of Maldives date back to Moresby's expedition to the atollsduring 1834 to 1836. However, these reefs were first studied in detail during Stanley Gardiner'sexpedition to the islands during 1899-1900 (PILLAI and SCHEER, 1976). The results of hisexpedition were published in two volumes (GARDINER, 1903-1906) containing elaborate discussionson the reef formations of Maldives and Laccadives, and systematic analysis of the zoological andbotanical specimens collected. Gardiner was followed by Alexander Agassiz, who spent two monthsmising through the archipelago in 1901-1902 (AGASSIZ, 1903). However, his work is consideredless scientifically valuable than that of Gardiner (STODDART, 1966).DERANIYAGALA (1956) made a collection of specimens from the Maldivian reefs in 1932for the Colombo Museum. This was followed by John Murray Expedition, led by R.B. SeymourSewell (1933-1934), which conducted gravity surveys and deep soundings in the Maldives andpublished physiographic descriptions of Addu and Goifurfehendu Atolls (SEWELL, 1936).Although several subsequent expeditions visited the Maldives, no major contributions weremade to the knowledge of the corals and coral reefs of these islands until the 'Xarifa' Expedition led byHans Hass in 1957. Based on the work done in Addu Atoll during this expedition, HASS (1962,1965) formulated a new hypothesis on atoll formation. PILLAI and SCHEER (1976) described andsummarized the geographical distribution of 143 species of hermatypic corals belonging to 49 generaand 4 ahermatypic corals belonging to 3 genera collected during this expedition. They also listed atotal of 241 species of corals belonging to 75 genera from the Maldives together with their knownoccurrence at the various atolls.A subsequent major study the reefs of the Maldives was made in 1964 by a team of scientistsfrom the University of Cambridge led by D.R. Stoddart. STODDART (1966) studied thegeomorphology of Addu Atoll and zonation of corals (STODDART et al., 1966; DAVIES et al., 197 1;STODDART, 1972), coral fauna (WELLS and DAVIES, 1966; CLARK and DAVIES, 1966) andother aspects of the Maldives. PURDY (1981) discussed the possible evolution of the Maldive Atollsbased on a combination of seismic stratigraphy and the results of a single well.The Maldive reefs have a high diversity of coral species, with a total of 241 species of hardcorals belonging to 75 genera (PILLAI and SCHEER, 1976). Available information indicates thatmany of the reefs studied in the Maldives are in a fairly good condition, with a live coral cover ofbetween 70-80 percent for Addu Atoll, 40-70 percent for Rasdu Atoll, 60-90 percent for FadiffoluAtoll and 20-50 percent for Ari Atoll (SCHEER, 1974). There is no mention of any human or otherfactors contributing to the deterioration of the Maldivian reefs. Although coral rock is used in someislands as building material and some reefs have traditionally been exploited for fish and shells, noimpact of these activities on the coral reefs has been recorded at these islands. Sporadic use ofexplosives to catch fish is apparently carried out in some islands.156