Status of Coral Reefs of the World 2000

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Status of Coral Reefs of the World: 2000 GEOGRAPHY, ENVIRONMENT AND POLLUTION Because of the north-south orientation of East Africa, there is a strong temperature gradient in the coastal waters of this region with a peak in the mid-latitudes of approximately 4-15 o S (southern Kenya to northern Mozambique), and lower temperatures to the south and north. This geographic variation had a particularly strong influence on the health and status of reefs during 1998 when the region experienced the major El Niño climate event. The East African coast is strongly influenced by river discharges and high nutrient levels, which affects coral reef distribution at both regional and local scales. Large expanses of the central Mozambique coast (800km) are devoid of reefs due to discharges from the large Limpopo and Zambezi rivers. Many fringing reefs have breaks opposite short coastal rivers that empty through deep mangrove creeks. The few measures of nutrient concentrations show high levels compared to other reefs systems, which are consistent with low levels of water clarity due to increased plankton and sediment loads. Information on coral reef status along the Indian Ocean coast of Somalia is poor, though patch reefs are known to extend to Mogadishu. It is likely that reefs do extend as far as the Horn of Africa, with expansion of many reef organisms onto the Socotra Archipelago (see Chapter 3). South Africa The coral reefs and coral communities of South Africa lie between 26-27 o S. These are the most southerly reefs in the western Indian Ocean. They are generally deep (below 8m), offshore, have high energy banks, and normal temperatures ranging from 22-26 o C to 29.5 o C. The reefs grow on a narrow continental shelf only 2-7km wide, which is remote from major human populations. The principal use of the reefs has been for game fishing and diving. Mozambique The 2,700km coastline extends from 26 o S to 12 o S, encompassing a full spectrum of reef types from the high latitude reefs of South Africa to the fringing and island reef complexes along the Mozambique-Tanzanian border where the South Equatorial Current meets the 66
Status of Coral Reefs in East Africa African coastline and splits north and south. The main reef system stretches for 770km from the Rovuma River in the north, to Pebane in the south (17 o 20’S). Smaller isolated reefs are dispersed along the 850km southern coast from Bazaruto Island to Ponta do Ouro (26 o 50’S). Mozambique’s coastal population was estimated at just over 6.66 million people (42% of the total) in 1997. Artisanal and commercial fishing, and tourism are the dominant uses of coral reefs in Mozambique. Tanzania Two thirds of the 1000km coastline supports fringing and patch reefs on a narrow continental shelf. The main areas of reef growth are along the islands of Unguja (Zanzibar), Pemba and Mafia, and the mainland coast at Tanga, Pangani, Dar-es-Salaam Mkuranga, Lindi and Mtwara. Tanzania’s coastal population was estimated at 8 million people in 2000, and is concentrated in the districts around the capital Dar es Salaam. Coral reef use is varied, with fishing and tourism supporting local and national economies. Kenya A continuous fringing reef dominates the southern 200km of Kenya’s coast. The fringing reefs in the north are more patchy with influences from river discharges and influenced by colder water from seasonal upwelling of the Somali current system. Kenya’s coastal population in 2000 has been estimated to reach 2 million people, concentrated around the main port of Mombasa. As with Tanzania, reef-based fishing and tourism are important components of the coastal economy. PRINCIPAL THREATS AFFECTING CORAL REEFS: 1998-2000 El Niño There was a strong south-north gradient in the extent and impacts of the El Niño bleaching event of 1998, which elevated normally warm local temperatures. Coral bleaching and mortality started in the south in late February to early March 1998, and finished in May in the north, directly corresponding to the ‘movement’ of the sun as it passed through the Inter- Tropical Convergence Zone. There were dramatic losses of coral cover (summarised below). After 1998, there were significant increases in fleshy, turf, calcareous and coralline algae growing on the newly dead coral surfaces on all reefs, which in turn was influenced by an abundance of herbivorous fish populations. The algae grew larger and more rapidly in areas where there were large reductions in herbivore fishes due to over-fishing. These coral to algal community shifts happened less in protected fish reserves. Non-reef building coelenterates (cnidarians), including anemones, corallimorphs and soft corals were also heavily damaged by bleaching and mortality on many reefs through East Africa. Changes in coral eating animals were minor, but there were some increases in herbivore populations, such as on Mafia Island. • South Africa: The bleaching threshold for corals was exceeded for both hard and soft corals, but it was not excessive. Most corals on the reefs grow at 12m or deeper, which may have protected them from warmer temperatures in surface waters. Soft corals are more prevalent on shallow reef tops, with more conspicuous bleaching. 67
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FOREWORD Over the past few years, I
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CONTENTS COUNTRIES, STATES AND TERR
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COUNTRIES, STATES AND TERRITORIES A
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Countries, States and Territories T
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EXECUTIVE SUMMARY CLIVE WILKINSON T
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Executive Summary CORAL BLEACHING I
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Executive Summary South Asia Most r
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Executive Summary parts of Fiji and
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8. STATUS OF CORAL REEFS OF EAST AN
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Status of Coral Reefs of East and N
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9. STATUS OF CORAL REEFS OF AUSTRAL
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Status of Coral Reefs of Australasi
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10. STATUS OF CORAL REEFS IN THE SO
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Status of Coral Reefs in the Southw
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11. STATUS OF SOUTHEAST AND CENTRAL
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Status of Southeast and Central Pac
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12. STATUS OF CORAL REEFS OF AMERIC
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Status of Coral Reefs of American S
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15. STATUS OF CORAL REEFS IN THE NO
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Status of Coral Reefs in the Northe
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17. STATUS OF CORAL REEFS IN THE EA
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Status of Coral Reefs in the Easter
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18. STATUS OF CORAL REEFS IN SOUTHE
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Status of Coral Reefs in Southern T
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19. SPONSORING ORGANISATIONS, CORAL
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Sponsoring Organisations, Coral Ree
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LIST OF ACRONYMS AGRRA AIMS ASEAN B
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