The Western Indian Ocean is distinctive in terms of coral reefs. Its eastern boundary is marked by the Seychelles and the shallow Mascarene Ridge which extends down towards Mauritius. East of these is a considerable expanse of deep ocean separating the reefs of this region from those of the Maldives and Chagos. The region's southern margin are the oceanic waters to the south of Mauritius, Reunion and Madagascar, while on the continental coastlines of southern Mozambique and northern South Africa the gradual cooling of water temperatures is mirrored by a decrease in coral diversity. The growth of reefs ceases close to this international border. The northern edge of the region ends along the eastern coast of Somalia where coral growth again becomes highly restricted, here by cold water upwellings associated with regional patterns in oceanic currents.

The reefs on the mainland coast of Africa are predominantly fringing, closely following the coastlines of the mainland and islands on the continental shelf. Madagascar has some discontinuous fringing reef development, as well as some barrier reef systems off its west coast. The remainder of this region is dominated by oceanic islands. The northern Seychelles are actually a remnant of the continental crust, with high islands and fringing reef systems.

The reefs of this region have high levels of species diversity, and although they are similar to those of the Central Indian Ocean, there are distinctive and endemic species which have led to the recognition by some authors of a Western Indian Ocean center of diversity. Human populations along much of the coastline are rapidly increasing, mostly poor and heavily dependent on the adjacent reefs for food. Unfortunately there is little control over the utilization of these resources, either though traditional or formal management, and large areas of coral reef have been degraded by over fishing or destructive fishing practices. Growing interest in the reefs for tourism is leading to new pressures in some areas, however it is providing an economically powerful incentive for protecting reefs, and there is considerable potential for environmentally sustainable tourism developments.  

Kenya has fringing reefs are fairly well developed along the southern coastline, however, to the north, where there are large areas of loose sediment and significant freshwater influences (the Athi-Galana-Sabaki and the Tana rivers), levels of reef development are much lower. Patterns of biodiversity appear to follow patterns of reef development with generally higher diversity in the south. Active coral growth is not continuous along the fringing reefs, but is interspersed with extensive seagrass and algal beds. Important mangrove communities are also found on the leeward shores of the offshore islands and on their corresponding mainland coasts. There are also important nesting communities of terns and seagulls on a number of offshore islands, notably the barrier islands in Kiunga.

Coastal areas of Kenya are densely populated and there are large scale local and commercial fisheries. Exploitation of fish of all types is heavy and stocks in several localities are considered to be overexploited. A number of marine parks and preserves have been established where fishing is either prohibited or restricted to traditional, less destructive, methods. Protection of these areas has had clear impacts, with increases in fish abundance and diversity as well as live coral cover.

Tourism is a major industry in Kenya and diving is a popular activity on many of the southern reefs. Overexploitation is a continuing problem on Kenyan reefs, including illegal activities in protected areas, although policing is increasingly effective in places.

Southern Somalia
The coastline of southern Somalia in many ways continues the patterns of coral reefs found off northern Kenya. Fringing reefs are relatively well developed in the south and around the islands of the Bajuni Archipelago, but further north the diversity and abundance of living coral decreases, although fossil structures remain. Data on biodiversity are unavailable for southern Somalia but it is likely that the trend of decreasing diversity towards the north continues. Political instability in southern Somalia has prevented the gathering of information about the reefs or their utilization by local human populations for a number of years. There are currently no effective legal controls on the exploitation of natural resources, and these are clearly not a priority. In some areas natural resources may actually be protected by such instability, but over exploitation is likely to be an issue.

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Reef Base: Somalia

The Tanzanian coastline runs approximately north-south and is dominated by three large offshore islands, Pemba, Zanzibar and Mafia. Coral reefs are well developed in many places. Close to the mainland there are fringing and patch reefs along much of the coast to the north of the Pangani River, with a wide lagoon with only occasional patch reefs further south around Dar es Salaam.. Coral cover is highly varied, and in some areas, reefs are not actively developing. Coral diversity increases with distance from the coast and up to thirty-nine genera of coral have been reported from individual patch reefs off the Tanga coast. Offshore reefs are highly developed around the main three islands, their associated islets and the Songo Songo Archipelago in the south.

The coastal population in Tanzania is very large, mostly concentrated in Tanga, Zanzibar, Dar es Salaam and Mtwara. Rapid population growth along the coasts, combined with poverty and poor management and understanding of coastal resources, has led to the rapid and extreme degradation of coral reefs and other coastal communities along large sectors of the coast. Fishing is a critical activity, and over fishing is a problem on most reefs, and has been exacerbated by destructive fishing practices. Most notable among these are the various seine-net fishing techniques in which a small mesh net with a weighted foot rope is dragged along the bottom, either onto a beach or into a boat. Dynamite fishing was also once widespread, but its use had been drastically reduced throughout the country following a nationwide campaign in 1996-97. This involved major community-driven action which included naming culprits, but also an amnesty for all those who surrendered their dynamite and made a public statement not to re-offend. Coral mining is another destructive activity which is also widespread along the entire coast. In 2000 it was estimated that 1500 tons of coral were being mined every year from the Mikindani Bay area in southern Tanzania alone. Some twelve percent of Tanga's reefs are believed to be totally destroyed, largely through destructive fishing, and a further sixty-four percent  are in poor to moderate condition.

The is only primary sewage treatment in Zanzibar Town, and little or no treatment on any of the mainland coast. Tourism is a growing and important sector of the economy, but there are few environmental controls and there may be increasing impacts on the reefs. Nevertheless, tourism is also providing impetus for further reef protection measures in a number of areas. The Chumbe Island Coral Park provides the best example of "low impact" tourism in the region, and tourism here provides support not only for reef management, but also for an important education program with schools and local communities in Zanzibar.

Although a number of marine reserves were designated in 1975 none of these was fully implemented. Subsequent legislation under the Marine Parks and Reserves Act in 1994 rectified this situation and there are now five marine reserves and two marine parks designated under this act. The latter are large areas, incorporating reefs and other ecosystems, with zoning systems and focused towards sustainable use

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Reef Base: Tanzania

Mozambique has a long coastline facing the Mozambique Channel and Madagascar. Fringing reefs are common along the northern coastline away from river mouths and around the offshore islands, with mangroves and patch reefs on the western shore and simpler reef profiles along exposed eastern shores. The central section of the coastline has been called the swamp coast and is dominated by river sediments. These prevent major reef developments, while there are extensive mangroves inshore. Further south again, reef development is limited, but there are true reefs as well as rocky structures with coral communities around both the Bazaruto and Inhaca Islands.

Of note, probably the largest remaining population of dugongs is found in the Bazaruto Archipelago, estimated at 150 individuals in the early 1990's but thought to have declined to 60-80 animals by 1999.

Mozambique also has a large coastal population and a majority of these people moved to urban areas during the civil unrest which ended in 1992. These urban centers are a major source of considerable pollutants to nearby coastal waters as most sewage is untreated. Away from these urban areas much of the coastline is dominated by slash and burn agriculture, which releases sediments and nutrients into nearby waters with devastating effects. Tourism is growing, particularly in the south, and is generally considered detrimental to the environment, especially vehicular based or camping-based tourism from South Africa which brings few benefits to the country,  and may lead to unsustainable levels of recreational fishing and damage to turtle nesting beaches. Efforts to develop coastal resorts have also been poorly controlled to date, although this may be changing. Most reef-based tourism operates around the Bazaruto Archipelago and there is evidence of significant damage to reefs caused by divers and boats.

Mozambique does have many reefs which have escaped heavy human impact, however this also is changing  and quite rapidly in some areas. There are only two protected areas which incorporate reefs, and while there are active management measures in place at these sites, there are no immediate proposals for any protected areas on the important reefs north of the country.

South Africa has three main areas that have reef communities, although these are not considered to be true coral reefs. These are the northern, central and southern reef complexes. Diversity is lower than the reefs of the more northern countries, with only forty-three species of scleractinian coral recorded. Large numbers of divers visit the reefs, with over 90,000 recreational dives per years, mostly visiting the Two Mile Reef in the central complex. Lying offshore, these areas are not threatened by terrestrial sources of pollution or sedimentation, and they are protected within the St. Lucia Marine Reserve (a part of the wetland park).

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Reef Base: Mozambique
World Wildlife Fund "Expeditions in Conservation-Mozambique"

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Madagascar is one of the world's largest island. Along with the Indian sub-continent it was separated off the rest of Africa during the Jurassic, and was then separated from the Indian sub-continent during the late Jurassic/early Cretaceous. There are clear differences between the physical conditions and resulting ecological communities on the east and west coasts.

The east coast is steep, and in places, mountainous. This is matched by a steeply shelving bathymetry and narrow continental shelf. The central and southern sections of this coast are dominated by vast sandy beaches and barrier islands and there is no offshore development. Further north the coastline becomes more complex, with a number of embayments and rocky headlands as well as offshore islands. There are a number of emergent fossil reefs along the more northerly sections of this coastline, and active coral growth is also widespread in the north, often growing on fossil structures offshore, although not always contributing to active reef development. There is a submerged and fragmented barrier reef described off Toamasina, although the recent status of this is unclear. Discontinuous fringing reefs also occur off the coast around Foulpoint and Mananara, Nosy Boraha (Saint Marie Island) and the Masoala Peninsula.

The west coast of Madagascar consists of a wide coastal plain, with numerous rivers, and also a wider continental shelf. This coast is swept by the northward flowing currents of the Mozambique Gyre and is further affected by large tidal ranges. Reef development is extensive in both the northern and southern parts of this coast. The southernmost reefs are offshore around Banc de l'Etoile and Nosy Manitsa. There are extensive fringing reefs along much of the coast north of Androka as far as Cap St. Vincent, varying between 500 meters and a few kilometers offshore, and separated from the shore by a generally narrow channel. Around Tulear a more complex system of offshore reefs is present, with shoreline fringing communities, a series of inner lagoon reefs , and a well developed barrier reef -the Grand Recif -which runs continuously for eighteen kilometers. Between the Baie des Assassins and Morombe a sequence of reefs, many with associated sand cays, has developed offshore, forming a fragmented barrier reef system. This same barrier system reappears north of the Mangoky Delta with a series of submerged banks and emergent reefs with sand cays. Along most of the central section of the west coast there is no reef development, probably due to the sediments discharged from the rivers. Offshore, however, there are reefs towards the edge of the continental shelf associated with the Iles Barren and the Banc du Pracel, although these main poorly documented. In the northeast, fringing reefs appear along the coast and the offshore islands, notably Nosy Be and the Mitsio and Radama Archipelagos, although their distribution is discontinuous around the many rivers and bays. On the outer edge of the continental shelf  in the far north, there is another series of raised banks, actually forming a near continuous ridge which my be the remains of a large barrier reef system. Coral cover is reported to be very high along the outer slopes, heavily dominated by formations of the sheet coral Pachyseris speciosa.

Most research has been centered around Nosy Be in the north and Tulear in the south, and very little is known about the intervening reef areas. Some 130 species of scleractinian coral and 700 fish species have been recorded on the reefs off Tulear, but it has been estimated that there may be 200 coral species and 1500 fish species in the whole country. Along the western coastline, mangroves form a major community and seagrasses are widespread, often forming the dominant communities in the channels behind fringing reefs.

For its size, Madagascar is relatively sparsely populated, with the estimated population just over 15,000 persons. The majority of coastal population is concentrated on the eastern coast, while the western coast is less developed, aside from the larger cities of Tulear and Mahajanga. It is this west coast, however, that also supports the majority of fishing and tourism-based activities. Artisanal fishing is a critical activity, accounting for an estimated fifty-five percent of all fisher production from an estimated 1,250 fishing villages operating over 20,000 small vessels (pirogues, mostly without engines). Reef-associated species are heavily relied upon, accounting for
 forty-three percent of total production. It remains a largely traditional fisher, although there are increasing numbers of migrant fishermen who do not observe local customs or taboos. Larger scale commercial and export fisheries make up the reminder, and together with aquaculture, provide critical foreign exchange earnings. Tourism is another important and relatively rapidly developing activity, with at least fifty percent of arrivals visiting the coast.

One of the greatest threats to Madagascar's reefs is silt from inappropriate land use practices. Most of Madagascar's land area has been converted from natural systems and soil erosion affects nearly eighty percent of the island, with massive sedimentation offshore. Urban and industrial waste is poorly controlled and a problem near major cities. Over fishing may be significant -fishing levels have greatly increased in recent years and there is evidence of reduced yields. Despite the considerable potential for ecotourism most developments seem to have been poorly planned and contribute to pollution, while also causing conflicts with local fishing communities. There is only one marine protected area with coral reefs, the Mananara Marine National Park on the northeast coast which incorporates three coral islets, including Nosy Antafana. This site has two rangers and there is some community involvement in its management. There are also a number of proposals for new parks.

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Reef Base: Madagascar


There are a number of small oceanic islands lying between Mozambique and Madagascar. The most important of these are the four large volcanic islands of the Comoros Archipelago situated at the northern entrance to this channel.  Mayotte, the easternmost of the islands, is a collectivite territoriale under French control, while the remaining islands form the Federal Islamic Republic of the Comoros. Mayotte is geographically the oldest and is surrounded by a wide lagoon which reaches some seventy meters in depth before a barrier reef some 3-15 kilometers offshore. The remaining islands are surrounded by fringing reefs.

Mayotte's reefs are relatively well studied, and harbor more than 200 species of coral. Fisheries and tourism are important activities, with some 3,600 fisherman and 9,000 visitor arrivals per year in the late 1990's. Two protected areas have been established, although these only cover some two percent of the total area of the lagoon. A comprehensive management plan for the lagoon was under development in 2000.

Comoros is densely populated  and is one of the world's poorest countries. Deforestation and conversion of land to agriculture are creating massive problems of soil erosion, which is affects large areas of reefs offshore through siltation. Reef walkers by fisherman gathering octopus and small fish is also causing some degradation of reef flats, and blast fishing is reported to be a problem on Mwali.

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The Seychelles is a large archipelagic island in the Western Indian Ocean. The 115 named islands and atolls together with their associated reef systems can be clearly divided into tow distinct regions: the high islands to the north and the low coralline islands spread over wide areas to the south and southwest.

The Seychelles Bank lies at the northernmost point of the Mascarene Ridge and is a large, shallow area of water, mostly above a depth of 100 meters. In its center are a number of high islands of continental origin which are surrounded by widespread but discontinuous fringing reefs. The low coralline islands to the south and west of the Seychelles Bank fall into a number of geographic groups and the reefs in these outer island areas are highly varied, and include true atolls, submerged or partially submerged atolls, and platform or bank structures. The Seychelles lies in an area of relatively high faunal diversity and some 101 hermatypic coral species and 920 fish species have been listed.

The reef fauna is fairly typical of the Western Indian Ocean, and human impacts on the reefs are varied, but clearly significant in the high islands. Most of the national fish consumption is of nearshore fishes, a large population of which are reef associated. The reefs of the Seychelles are therefore highly utilized, and there are clear examples of over fishing. In the southern islands however, fishing pressure is relatively low.

There is a clear awareness of environmental issues at the governmental level and efforts are being made to improve sewage treatment in some areas that have problems. A number of marine protected areas have been established and active management is underway. A good example of this enlightened policy is the remote island of Aldabra that has long been recognized for its unique flora and fauna and is well protected, with a research station and permanent staff.

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Reef Base: Seychelles

The Mascarene islands of Mauritius, Rodrigues and Reunion are all of volcanic origin and show a clear sequence of reef development.
Mauritius is almost completely encircled by fringing reefs, with substantial lagoon and barrier reef development on the east and southeast coasts. The lagoons are dominated by algae, but with some areas of seagrass. Rodriques is the oldest of the volcanic islands and has a highly developed reef structure, although a true barrier reef has not formed. The island is completely encircled by reefs, with wide shallow reef flats extending out from the shore.

Many of the reefs around Mauritius have been degraded by human activities, and problems include high levels of sedimentation and pollution arising from the clearance of forest and subsequent agricultural runoff. Further pollution comes from domestic and light industry, and coastal development spurred by tourism. By contrast, the island of Rodriques remains relatively undeveloped, with a small human population. Overall, the reefs here are in relatively healthy condition.

Reunion, a territory of France, has only a few fringing reef communities restricted to its leeward western shores, although corals are found growing directly on volcanic substrates in the southeast. The reefs here have been well studied and an estimated 1,000 species of fish are found in the surrounding waters, including 250-300 reef-associated species and 140 coral species. The majority of people on Reunion live close to the coast and have had a major impact on it. Over exploitation of coastal fishes has been occurring for some time, and destructive fishing practices have been reported.  Pollution and coastal development have also impacted the reefs of Reunion and efforts are underway to reduce impact, including implementing tighter controls of land-based sources of pollution.

Most of the reefs are formally protected within a marine park, which had eleven park rangers in 2000. The area incorporates a number of fishing reserves, while consideration is being given to the designation of nature preserves or other additional forms of protection within park boundaries.

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Extracted and adapted from The World Atlas of Coral Reefs, by Mark D. Spalding, Corinna Ravilious and Edmund P. Green, published by the University of California Press . For more complete and in-depth coverage of the topics presented in this webpage, I recommend highly purchasing a copy of this beautifully illustrated book. Just click on the University of California Press link above to do so.