Coral Reef Degradation in the Indian Ocean
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CORAL REEF DEGRADATION IN THE INDIAN OCEAN Status reports and project presentations 1999 – 1 – CORAL REEF DEGRADATION IN THE INDIAN OCEAN Status reports and project presentations 1999 Published by CORDIO SAREC Marine Science Program Department of Zoology Stockholm University 106 91 Stockholm Sweden ISBN 91-630-8329-9 Maps by Jeanette Bergman Weihed, Tellurit Datorgrafik Produced by Niki Sporrong Enkla Ord, Uppsala Layout by Tryckfaktorn AB, Hans Melcherson Printed by Erlanders Gotab, 1999 – 2 – Foreword Corals as organisms and coral reefs as structures and threaten these peoples livelihoods and endanger a large ecosystems have fascinated scientists for centuries. proportion of the world’s coral reefs, especially those Charles Darwin became well-known among natural adjacent to human populations. In addition, thermal scientists long before the publication of The Origin of pollution from power plants and the chemical industry Species, partly because of his studies of coral reefs and has contributed to coral damage in some industrialised coral islands. Undoubtedly, this fascination for coral areas. reefs is a direct result of the tremendous diversity of When corals become stressed, a typical response is species, exemplified by the overwhelming number of “bleaching” and it occurs when the symbiotic algae are fish of all shapes and colours, that inhabit the world’s lost from the tissue of the coral polyp. For short periods, richest marine ecosystem. the polyp can survive without the algae, but unless the Fundamental to the existence of coral reefs is the situation that caused the bleaching improves and new symbiosis between the reef-building coral polyp and the algae are incorporated into the tissue, the coral will die. algae, known as zooxanthellae, that resides within the Once dead, the reef is rapidly overgrown by other types tissue of the polyp. From an ecological point of view, of algae and the reef framework is eroded through coral reefs provide opportunities to observe interactions, actions of boring organisms. In certain regions of the such as predation, competition and synergism, between world, intact coral reefs act as barriers that protect reef-dwelling organisms, which furthers our under- coastal areas from oceanic waves. When the reef frame- standing of community ecology. The formation of work is degraded, the reef is no longer able to prevent structures like reefs and islands of coral sand also the passage of oceanic waves and, as a consequence, provide prime examples of interaction between biology some islands and beaches may be severely eroded. and geology. The destruction of coral reefs can also result in Films depicting coral reef communities have become drastic changes in the fish populations associated with very popular with the general public. This has not only these ecosystems. When a reef is healthy, species of fish made coral reefs more attractive as tourist destinations, that eat coral are abundant. However, when a reef it has also increased the general awareness of how these becomes degraded and many of the corals die and ecosystems function and how important they are become overgrown by algae, corallivorous fish are globally. For the human inhabitants of coastal and replaced by fish that are algal grazers. If the reef island communities in tropical and subtropical regions degenerates further, reef dwelling species of fish may of the world, coral reefs provide the very basis for a disappear and be replaced by species that are pelagic. sustainable livelihood. However, activities such as Ultimately, biodiversity, in terms of species of fish, dynamite fishing, deforestation causing siltation, shellfish and other reef inhabitants, plummets. This intentional use or accidental spill of chemicals, intensive leads to a drastic reduction in the catch of desired reef- tourism and the capture and trade of ornamental fishes dwelling fish by local fishermen that use traditional – 3 – fishing methods. As a consequence, the food security of corals as to the nature of stability and sensitivity of those dependent on coral reef fisheries is compromised, complex ecosystems. Such knowledge may prove thereby increasing the risks of poverty. invaluable in achieving sustainable development in a There have been reports of coral bleaching in the world experiencing widespread climatic change. past. However, the magnitude of the 1998 coral bleach- This report provides timely and important informa- ing event, that resulted in massive death of corals in the tion on the extent of coral mortality throughout the Indian and Pacific Oceans and the Caribbean Sea, has Indian Ocean. The data contained within the report will never been reported before. Despite a strong correlation provide a valuable reference point that will enable us to with extreme temperatures, the exact causes of coral determine the environmental and socio-economic bleaching are not entirely clear. Therefore, it is impera- consequences of the 1998 bleaching event. The findings tive, because of the importance of coral reefs for the of the report provide an important contribution to the food security and economy of human populations in design of future initiatives to alleviate ecological and tropical coastal and island communities of our globe, socio-economic impacts of coral bleaching. The COR- that understanding the reasons for coral bleaching be DIO program fulfils an important role and merits full given the highest priority. Furthermore, there are support. general lessons to be learned from this mass mortality of ARNE JERNELÖV Secretary General, FRN (The Swedish Council for Planning and Co-ordination of Research) INDU HEWAWASAM Environmental Specialist, World Bank ANDERS GRANLUND Head of Division, Sida (Swedish International Development Co-operation Agency) GÖRAN A. PERSSON Director, MISTRA (Foundation for Strategic Environmental Research) LARS KRISTOFERSON Secretary General, WWF-Sweden – 4 – Table of contents EXECUTIVE SUMMARY ARTICLES ON THE SCOPE OF CORDIO Remote sensing as a tool for assessing reef damage 67 RATIONALE Coral bleaching effects on reef fish communities and fisheries 71 STATUS REPORTS FROM DIFFERENT REGIONS Rehabilitation of degraded coral reefs 78 Coral reef ecosystems in South Asia 11 Socio-economic aspects of the 1998 coral bleaching Status report India 25 event in the Indian Ocean 82 Coral mortality in the Chagos Archipelago 27 Sustainable energy and wastewater treatment as alternative/ Status report Kenya 33 sustainable livelihood for costal communities 86 A preliminary assessment of coral bleaching LIST OF CORDIO PROJECTS 1999 in Mozambique 37 Assessment of the extent of damage, socio-economics East African region 93 effects, mitigation and recovery in Tanzania 43 South Asia region 96 Influence of coral bleaching on the fauna Central Indian Ocean islands 98 of Tutia Reef, Tanzania 48 Consequences of the 1998 coral bleaching event for the islands of the Western Indian Ocean 53 APPENDIX Status report Mauritius 60 Meeting agenda 103 Status report Socotra Archipelago 63 List of participants 105 – 5 – Executive Summary The reports in this volume summarize the extent of INDIAN OCEAN ISLANDS damage to the coral reefs of the Indian Ocean caused by • Coral mortality ranged from 50–90% over extensive the elevated temperatures in 1998. Most of the reports areas of shallow reefs in Seychelles, Comoros, also contain information on the status of reefs 6 to 12 Madagascar and Chagos. In some areas (around months after the events of 1998, thus describing the fate Mahe, Seychelles), mortality was close to 100%. of dead corals, the first signs of recovery in some areas, • By the end of 1998, algal turf covered coral reefs and the secondary damage to other organisms depend- throughout much of the region. ent on the reef, such as fish. A brief summary of the • Monitoring of potentially toxic, epiphytic dinoflagel- results is given here. lates has shown drastically increased concentrations in areas with dead corals. • By early 1999, much of the dead coral in Chagos was EAST AFRICA reported to be eroded to rubble, preventing recoloni- • Several areas suffered very high coral mortality. For sation. In Socotra Archipelago, coral rubble has been example, surveys in Kiunga and Malindi (Kenya), washed ashore and can be found in piles on the beach. Misali and Mafia (Tanzania), and Pemba and • Preliminary assessments of the reef fish communities Inhacca (Mozambique) showed that 90–100% of the in Chagos indicate that abundance and diversity have corals died after exposure to water temperatures that decreased to less than 25% of their former levels. exceeded 32°C, mainly in March and April 1998. The mortality of corals culminated around mid- SOUTH ASIA REGION May. In some areas, however, corals continued to die • Bleaching was reported down to a depth of 40 m in until October. Sri Lanka and 30 m in Maldives, as a result of water • Following the event in 1998, coral cover appears to temperatures of approximately 35°C during the have been reduced to between 10 to 50% of previous period April to June, 1998. levels in most areas along the coast of Kenya, • In Sri Lanka and Maldives, nearly 90% of the corals Tanzania and northern Mozambique. In some areas died in many areas. In the Hikkaduwa and Bar reefs the reduction is greater, i.e. up to or above 90%. of Sri Lanka, close to 100% of the corals died, and by • Initial investigations indicate that fish communities the end of 1998, these reefs were covered by thick associated with coral reefs were affected by the coral algal turf. In May 1999, large areas of reefs in mortality and that, in general, herbivorous species Maldives showed few signs of recovery. increased while corallivorous species decreased. • In India, surveys indicated mortality between 50 and • In most affected areas, the cover of algal turf on 90% in the reefs in Gulf of Mannar, Andaman bleached and dead reefs increased significantly. On Islands and Lakshadweep. Kenyan reefs, for example, algal cover in many areas • Assessments of the reef fish communities showed increased up to 200% as a result of the newly availa- drastic reductions in butterfly fish numbers in Sri ble substrate.