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1954) and 7,300 g C m-2 yrl (GORDON and KELLEY, 1962) have been determined for coral reefareas in the Indian and Pacific Oceans, but generally the gross productivity appears to fall within therange of 2,000-5,000 g C m-2 yr-l (see LEWIS, 1977). Estimates vary with the type of reef areaunder investigation, the methods used, and the assumptions made in the calculations.The corals themselves are partly responsible for the high primary productivity of reefs due tophotosynthesis occurring in their symbiotic zooxanthellae (YONGE, 1940, 1963). Corals have beenfound to fix carbon at rates equal to between 800 and 4,000 g C m-2 yr1 (KANWISHER andWAINWRIGHT, 1967). But also important, and perhaps frequently of greater magnitude, is theproductivity of the algal “lawn”, composed of diatoms, filamentous green algae and small red algae,that colonises most of the rocky surfaces of the reef in shallow water (DAHL, 1974; WALKER,1981). Such algal turf communities frequently occupy as much of the surface area of the reef as do thecorals, and it has been found (JOHANNES et al., 1972; SMITH and MARSH, 1973) that the primaryproductivity of reef areas occupied by algal turf is higher than that of adjacent areas dominated bycorals.The algal turf is intensively grazed by various types of fish, especially by surgeonfishes(Acanthuridae), parrotfishes (Scaridae), damselfishes (Pomacentridae) and blennies (Blennidae), aswell as by echinoids (sea-urchins)(RANDALL, 1961; BAKUS, 1966; DART, 1972; VINE, 1974;OGDEN and LOBEL, 1978), and this accounts both for the low standing crop in relation to turnoverand productivity, and the relatively high biomass of grazing species on the reef (RANDALL, 1963;HOBSON, 1974). The coral, however, remains critical to the fish production of the community bothin being responsible for the formation and maintenance of the shallow water substrata on which thealgal turf develops, and in providing the habitat complexity which may allow dense populations ofprimary and secondary consumers to survive despite an abundance of predatory species (COLLETTEand TALBOT, 1972; SMITH and TYLER, 1972; CROWDER and COOPER, 1979; SAVIN0 andSTEIN, 1982). Thus both coral and algal components contribute to the high primary productivity.As a consequence of this high primary productivity the standing crop of fish on reefs mayreach 5-15 times that in productive North Atlantic fishing grounds, and twice that for managedtaliperate lakes (STEVENSON and MARSHALL, 1974). It is su gested that maximum fish harveststhat can be sustained from coral reefs are probably 10-20 mt km- 5 . However, because of the patchynature of the reef habitat and its tight recycling of nutrients, total catches may not be as high as in majorfisheries in temperature and upwelling regions of the world’s oceans. Nevertheless, as pointed out byGOMEZ (1980), the importance of coral reefs as providers of fish and shellfish for home consumptionand local markets is probably underestimated.Besides their significance to fisheries, reefs are of considerable actual or potential value in anumber of other ways. They have proved invaluable for education and science, providing a suitablehabitat in which to study scientific problems of much wider significance. As a result of their highdiversity - individual reef sites may harbour as many as 3,000 different species of animal andplant - reefs represent a major genetic resource. Many reef animals have been found to containpharmacologically active compounds which may be of medical value or lead to advances in medicalresearch (CIERESZKO and KARNS, 1973; RUGGIERI, 1976). And other reef species may provevaluable for transplantation, exploitation or use in the development of mariculture (HESLINGA,1980).Also, coral reefs are generally regarded as being of considerable economic and social value forrecreation and tourism. The need to protect reef areas used by a developing tourist industry hasgenerally been accepted as a major impetus towards the establishment of marine parks and reserves,and such reserves have now been established in a wide variety of countries (see BJORKLUNG, 1974;OLINDO and ASAVA, 1975; ROBINSON et al., 1981; PERTET, 1982). Clear benefits have beenrecorded in, for example, the Netherlands Antilles (Bonaire Marine Park), Seychelles (Anne NationalMarine Park), Fiji (Tai Island) and Kenya (Malindi and Watamu Marine National Parks) (SALM,1983). Benefits are not easily quantified, and relevant data not generally available, but as an example,in 1981 there were 1,322,300 visitors to the Buck Island Reef National Monument in the U.S. VirginIslands (U.S. NATIONAL PARK SERVICE, 1981). Many Indian Ocean protected reef areas mustalso receive tens of thousands of visitors each year. Even where international tourism for leisure orwater sports may not be significant, reefs clearly have considerable recreational potential for the localpeople, and as standards of living continue to rise, demand for more sophisticated pastimes, such assnorkelling and diving will probably increase.168