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

mersas are known to serve as nursery areas for these species of shrimp (BRANFORD, 198l), andprobably do so in many areas of the Indian Ocean.Amongst fish the tiny Aphanias dispar is ubiquitous and very abundant in such lagoons inmany parts of the Indian Ocean, while commercial species characteristic of such habitats includeespecially mojarra (Gerridae), silversides (Atherinidae), grey mullet (Mugilidae) and juvenile emperors(Lethrinidae). As concluded by BARNES (1980), many of the most abundant lagoonal species appearto consume detritus, benthic algae and epiphytes rather indiscriminately, a generalisation that appliesnot only-to the fish but also to most molluscs, annelids and nektonic prawns.The significance of hypersaline conditions in limiting both primary and secondary productivityalso has been demonstrated in several other recent studies. PRICE (1982) described that within theArabian Gulf, the abundance of zooplankton is lower within embayments and is inversely correlatedwith salinity, and KAPETSKY (1981) has described how in Bardawil lagoon (on the EgyptianMediterranean coast) amelioration of hypersaline conditions, through maintaining continuousconnections with the sea, led to an increase in fish stocks.In general, however, there appear to have been few intensive studies of such enclosed baysand lagoons within the Indian Ocean, and in particular no extensive survey of their occurrence andsignificance throughout the region. Such survey work may be an important priority in view of the factthat such lagoon areas are especially subject to impact from various developments. They are especiallyliable to be affected by construction work because they can be potential harbours or boat channels, orare easily infilled; they are also attractive locations for the siting of private residences or commercialbuildings, and serve as a natural focus for recreational developments. They are also particularlysusceptible to pollution because of their reduced water circulation, so that pollutants discharged intothem tend to concentrate there. Besides industrial discharges, private houses clustered around a creektend to be built, in the absence of any regulations, so as to discharge their sewage and waste into thecreek, a practice that easily can result in local eutrophication. The many impacts that can affect a singlecreek or lagoon have been documented in various studies (e.g. BELLAN, 1972).CONCLUDING REMARKSIt is very apparent that critical habitats within the Indian Ocean are being subjected to anincreasing variety and seventy of impacts as a result of the increased pace of industrial and municipaldevelopment and the pressures of a greatly increased human population. Much of the damage to thesehabitats is direct damage or destruction to which these habitats are especially susceptible because oftheir coastal and near-shore shallow water locations. In fact, a recent review has concluded (UNEP,1985) that at the present time the impact on Indian Ocean habitats and resources due to pollution is asyet generally limited and confined to local areas, whereas, by contrast, the loss and destruction ofcritical habitats is now so extensive that, combined with widespread overfishing, during the last ten tofifteen years the potential fisheries yield of the region may have decreased by as much as 20%. Giventhe increasing food shortages in countries bordering the Indian Ocean, it must be considered an urgenttask to halt and reverse this acceleration in destruction of the region's renewable resources.A first step in this direction, save in countries such as Indonesia and Saudi Arabia where suchaction is already being taken, must be a survey of the occurrence, extent and significance of each ofthese critical marine habitats. This may be accomplished for some habitats in association with regionalprojects sponsored by the international agencies (UNESCO, UNEP and IUCN). Such survey workmust then lead to the development of an integrated coastal zone management plan. Through suitablecoastal zoning, areas of productive habitat can be guarded against unnecessary destruction by plannersor devefopers who may not realise their critical role in maintaining their country's renewable resources.183