Distribution of coral reefs

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4.5.1 Distribution of coral reefs

Hamilton 1975 collected, described and illustrated 88 species of scleractinian corals in East Africa. Hamilton and Brakel 1984 reported that the Region has 140 known species belonging to 55 genera 88 species belonging to 34 genera found in the Dar es Salaam area alone. In general, the exposed windward reef slopes were dominated by acroporids and pocilloporids in the turbulent upper zone and by poritids and faviids in the lower zone. Acropora and Galaxea clavus dominated sheltered reef slopes, while Pocillopora, Porites, Psammocora, and Pavona dominated reef flats. More recently, distribution studies in southern Tanzania have identified 51 scleractinian coral genera Horrill and Ngoile, 1992; Darwall et al., 1996; Guard et al., 1997, Darwall et al., 2000. Again, Acropora was found to dominate the shallow, sheltered inner reefs. In the Songo Songo Archipelago, Galaxea dominated many patch reefs, while two particular patch reefs, Poiasi and Pwajuu, were completely dominated by the fungiid Halomitra pileus . This species was also found to dominate an entire 200-m section of an outer reef adjacent to Msamgamku, Mtwara. Muhando 1995 found the dominant coral genera on reefs off Fumba Peninsula near Menai Bay in southwestern Zanzibar to be Acropora, Montipora, Porites, Millepora, Lobophyllia, Echinopora, and Favia. Along Tanga Region, there is 407 km of coastline, of which, 199 km are broken by bays and estuaries. Of the unbroken 208 km, 97 km 47 is bordered by 41 distinct sections of coastal fringing reef. In addition, there are 55 patch reefs, of which, 30 are outer patch reefs adjacent to the continental shelf and 25 are inner patch reefs located in near shore waters where water depth is less than 25 m. In total, there are 96 reefs in Tanga, having a total of 376 km of reef edge Horrill et al., 2000. Just north of Dar es Salaam city there is a series of reefs known as the Dar es Salaam Marine Reserves System which includes Bongoyo, Pangavini, and Mbudya Islands, which are surrounded by fringing reefs, and the patch reefs, Fungu Yasin and Fungu Mkadya Kamukuru, 1997. There is a number of other smaller patch reefs in the vicinity. Just south of Dar es Salaam city there are sections of fringing reef, particularly on the headlands ras in Swahili. There are also three chartered patch reefs as well as a number of other unchartered and unnamed reefs. Further north of Dar es Salaam, there are a number of patch reefs off the coast of Mbweni. Near Bagamoyo, there are stretches of fringing reef as well as several offshore patch reefs. Unguja Island, one of the two main islands of Zanzibar, is surrounded by scattered coral development. Along the northern, eastern and southern sides of the Island, there is a fringing reef, which is interrupted by Chwaka Bay. In addition, there are reef formations near Mnemba, a small island to the northeast, Leven Bank to the north and Bedford Bank to the south. On the western side of Unguja, there are a number of islands and patch reefs between Ras Nungwi and Menai Bay Horrill et al., 2000. Pemba, the second of the two main islands of Zanzibar, is estimated to have 1100 km of reef, representing 45 of the coral reefs of Tanzania. Coral growth has been observed as deep as 64 m. Misali Island, a small island on the western side of Pemba, has reefs of very high diversity of coral and fish species Horrill et al., 2000. In southern Tanzania, there are numerous patch reefs and fringing reefs around islands in the Mafia and Songo Songo Archipelagos. There are also numerous reefs along the Mtwara coastline.

4.5.2 Coral recruitment