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

Mining of Reef RockMining of reef rock from active reefs for road building, construction and lime production hascaused extensive damage to reefs, especially in India, Lakshadweep, Sri Lanka, and to a lesser extentin countries of the eastern Indian Ocean. For example, in India fifty boats were engaged in quarryingthe reef in Palk Bay, and by 1973 much of the reef had already been destroyed (PILLAI, 1973);extensive quarrying occurs at many sites in the Gulf of Mannar, at one site alone 30 boats removing30,000 m3 of reef per year (VENKATARAMANUJAM et al., 1981).Dynamiting and Other Destructive Fishing Met:iodsThe use of dynamite to kill and collect reef fish is not uncommon in countries from Egypt toKenya and Tanzania to Sri Lanka. It is even prevalent in various protected areas; for example, damageto the Tarutai National Park in Thailand (ALEXANDER, 1983) is attributed in part to fish blasting.Dynamiting not only kills numerous non-commercial fish, but destroys the coral environment whichprovides food and shelter for the fish, thus reducing or eliminating the possibility of subsequentcatches.Six further impacts may be noted as having caused significant damage to some Indian Oceanreefs, and may also be emphasized because of the damage they are known to have caused in other coralregions.Tourists and VisitorsThe extent of damage to reefs and reef communities by souvenir collection and other touristactivities is increasingly appreciated, and within the Indian Ocean has been especially noted in Kenya,Sri Landa and Egypt. Such damage has been a major impetus for the establishment of marine parksand reserves (see BJORKLUND, 1974), since without control tourists or souvenir merchants collectcorals and shells (JOHANNES, 1975; WELLS, 1981) and corals may be damaged by looking forshells or by trampling by fishermen or visitors. Significant coral damage also may be caused by theanchors of visiting boats (DAVIS, 1977). Visitors also may affect the abundance of important fishspecies by excessive spearfishing, thus competing with local fishermen, as well as potentially alteringthe ecology of the reef. Similar in nature are the effects of excessive collection of aquarium fish,recognised as a particular problem in Sri Lanka. Such over-exploitation can deplete considerably thepopulations of a variety of fish species (LULOFS, 1973; LUBBOCK and POLUNIN, 1975).Over-Exploitation of Food SpeciesIncreasingly reef fish and reef animals in many areas are being over-fished and over-exploited.Without controls the number of commercial fish species taken from reefs on over-populated tropicalshores has led to a decrease in yield below that which, in theory, could be sustained (JOHANNES,1981). Many other edible or semi-edible reef animals are being collected to near extinction, includingmany molluscs, especially giant clam (Tridacna spp.) and conch (Lambis spp.), echinoids andholothurians, crabs, crayfish and other crustzea.Oil PollutionThe effects of oil pollution on corals was recently reviewed by LOYA and RINKEVITCH(1980). It was initially thought that corals were relatively unaffected by oil pollution, and, followinglarge oil spills reefs, they were found to be significantly less impacted than other tropical marinecommunities (RUTZLER and STERRER, 1970; SPOONER, 1970). However, it appears that theextent of damage depends on the circumstances. Large spills can float over sublittoral reefcommunities and any toxic chemicals diffusing below the surface layer are soon dispersed.171