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Ecoregion Description
564: Coastal East Africa
Major Habitat Type:
tropical and subtropical coastal rivers
Author:
Dalmas Oyugi, National Museum of Kenya, Nairobi, Kenya; Michele Thieme and Ashley Brown, Conservation Science Program, WWF-US, Washington, DC, USA
Reviewers:
Lucy Kashaija, World Wildlife Fund – Tanzania Programme Office, Dar es Salaam, Tanzania
Countries:
Malawi; Mozambique; Tanzania
Boundaries:
This ecoregion, situated along the eastern coasts of Tanzania and Mozambique, extends from the Wami River basin southwards to the Luala River basin, directly above the Lower Zambezi basin [561]. The ecoregion includes Lakes Chilwa and Chiuta, the Ruaha/Rufiji, Ruvuma, and Lúrio Rivers, as well as other smaller coastal basins.
Drainages flowing into:
Indian Ocean
Main rivers or other water bodies:
From north to south, the major river drainages are the Wami, Ruvu, Rufiji (whose tributaries include the Great Ruaha, Kilombero, Luwego, and Mbarangandeu), Matandu, and Mbemkuru. The Wami River drains the Nguu, Nguru, Ukaguru and Rubeho Mountains of the ‘Eastern Arc’ mountain range. The shorter Ruvu River flows from the Uluguru Mountains onto the coastal plain. The Rufiji River, the largest in Tanzania, has several major tributaries, including the Ruhudji, with floodplains along the Kilombero Valley (up to 6,265 km2), the Great Ruaha, Njombe and Luwegu rivers. These rivers have their major headwaters in the Udzungwa and Mahenge Mountains of the Eastern Arc and the more southern Kipengere Range (Southern Highlands). The Rufiji is lined by a number of small temporary and permanent lakes that includes the Tangalala Lake Complex, a series of connected lakes (Manongi 1993). Larger rivers of northern Mozambique include the Ruvuma, Messalo, Lúrio, Mocubúri, Ligonha, and the Licungo, all of which drain the highland interior (900-2,500 m asl) to the coastal plain. The Ruvuma River is the third largest in Mozambique and has a catchment area of 155,400 km2 (Hughes & Hughes 1992). Swamps that line the lower reaches of the Ruvuma include the Nhica (75 km2), the Quitemba (25 km2), and the Miula (70 km2). Lake Nangade and several other oxbow lakes also occur in the river’s floodplain. Lakes Chilwa and Chiuta are shallow lakes at the headwaters of the Lugenda River, a tributary of the Ruvuma River. South of the Ruvuma, the Messalo, Montepuez, Megaruma, Lúrio, Mocubúri, and Monapo Rivers all have seasonal flows and most are lined by swamps. The lower courses of several of these rivers expand out into narrow, long lakes, such as Lake Biribizi on the Montpuez River (Hughes & Hughes 1992).
Topography:
In the Tanzanian portion of the ecoregion, rivers descend from the escarpments and highlands of the interior to the narrow coastal plain (15 km to 30 km wide).
Climate:
The climate is dominated by three features: the wet southeast trade winds off of the Indian Ocean, the southwest monsoon system from the Congo basin, and the northeast trade winds from Ethiopia and Somalia (Hughes & Hughes 1992). Rainfall is high (1,800-3,000 mm) in the highlands of this ecoregion, particularly in the Uluguru and Udzungwa Mountains in Tanzania, which are under the direct climatic influence of the Indian Ocean (Lovett et al. 1997) and in the Kipengere mountains where the Ruaha has its headwaters. Along the coast, rainfall is lower with an average of about 1,100 mm/year at Dar es Salaam, and an average of 800-900 mm in Mozambique (Hughes & Hughes 1992). Rains occur between January and October, depending on location within the ecoregion, with rains beginning later in the year, as one moves south. Rains occur in Tanzania between March and May and then begin again in October and November. Temperatures range from about 20o C to 32 o C along the coast in Tanzania to as high as 40o C in the south, although temperatures are significantly moderated by altitude and frosts can occur in the headwater mountains during the austral winter months (Hughes & Hughes 1992).
Freshwater habitats:
The habitats in the ecoregion include forested headwater streams, medium-sized rivers and their tributaries, mangrove forests, estuaries, small lakes, permanent swamps, dambos, deltas, and seasonal floodplains. Lake Chilwa is a unique, closed system with extensive Typha swamps, saline waters, and highly variable lake extent and water quality.
Terrestrial Habitats:
Vegetation adjacent to and within the freshwater systems of this ecoregion consists primarily of a coastal mosaic including large areas of miombo woodland, coastal dry forest and coastal scrub, riparian and swamp forests, floodplain vegetation, and mangrove forests (Hughes & Hughes 1992; Hatton & Munguambe 1998; Burgess & Clarke 2000). Swamp and riparian forest trees include Pandanus rabaiensis, Baikiaea insignis, Syzygium cordatum, Ficus verruculosa, F. trichopoda, Voacanga thouarsii, Raphia farinifera,and Parkia filicoidea. Cyperus papyrus also grows in permanent swamps lining the rivers, often in association with Phragmites spp. and Nymphaea capensis (Hughes & Hughes 1992). Grasses such as Echinochloa pyramidalis, Cynodon dactylon, and Oryza spp. dominate many of the floodplains of the ecoregion, whereas hygrophilous (living or growing in moist places) grass species such as Andropogon schirensis, Digitaria milanjiana, Loudetia phragmitoides, and others dominate dambos (seasonally waterlogged, predominantly grass-covered, shallow depressions in the headwater zone of rivers that are generally less than 5 km2) within the ecoregion (Hatton & Munguambe 1998). Mangrove forests line river mouths throughout the ecoregion (Hughes & Hughes 1992; Kemp et al. 2000). The montane headwaters of the rivers in this ecoregion are clothed with montane cloud forests, which are rich in endemic species of plants and animals (Lovett & Wasser 1993; Burgess et al. 1998).
Fish Fauna:
Characins, anguillid eels, rivulins, cyprinids, gobies, and mochokids are the most speciose groups in the fresh waters of this ecoregion. The fauna of the Lakes Chilwa and Chiuta system is typical of the East Coast bioregion, including Barbus atkinsoni, B. zanzibaricus, Bagrus orientalis and Pareutropius longifilis.
Description of endemic fishes:
About thirty percent of the -nearly 100 described fish species are endemic. Among endemic fish, there is a radiation of the Aplocheilidae genus Nothobranchius, with nine endemics known from this ecoregion (Lévêque 1997). The Cichlid Haplochromis tweddlei is, as yet, known only from Lakes Chilwa and Chiuta and may be endemic to the larger Ruvuma system (Roberts 1975; Tweddle 1983).
Other noteworthy fishes:
The presence of the tank goby, Glossogobius giuris, in Lake Chiuta suggests there is (or historically was) no barrier to upstream movement of fishes in the Ruvuma/Lugenda River system. The absence in the Chilwa catchment of Chiuta species Mormyrus longirostris, M. cf. brevianalis, Labeo sp., B. orientalis and Synodontis sp. is probably related to a lack of a suitable habitat and historical access. The absence of G. giuris is less easy to explain as it can survive in saline conditions.
Other noteworthy aquatic biotic elements:
The mountain headwaters of this ecoregion are less well known. A rich frog fauna is dependent on the moist mountain conditions and includes a number of endemic species. Over sixty species of aquatic-dependent frogs are known from the mountainous region in southern Tanzania alone (includes the Kipengere, Livingstone and Udzungwa mountain ranges), seven of which are endemic. Several of these species are in the Hyperoliidae family, including Hyperolius kihangensis, known from swamps in the dense evergreen forests of the Udzungwas (Schiøtz 1999). The recently described Kihansi spray toad, Nectophrynoides asperginis, lives only in the fine mist created by the cascading waters of the Kihansi Falls in the Southern Udzungwa Mountains. Limited investigation has also shown that some of the ‘Eastern Arc’ Mountains of Tanzania contain an important assemblage of Odonata (dragonflies and damselflies) – including endemic species of the genera Umma and Chlorocnemis that are more commonly found in the Congo Basin (Clausnitzer 2001). The lowland coastal forests also support important dragonfly assemblages, including Coryphagrion grandis - a Gondwana relict species whose nearest relatives are found in Central and South America (Clausnitzer 2001).
This ecoregion’s riverine habitats provide good habitat for wetland birds. The productive swamps and floodplain lakes of the lower Ruvuma River provide extensive habitat for a rich avifauna, including large numbers of weavers. The Kilombero floodplain also provides habitat for the endemic Kilombero weaver (Ploceus burnieri), which breeds in extensive riverine swamps fringed with Phragmites mauritianus (Stattersfield et al. 1998; Baker & Baker 2001). Other important wetlands for birds within this ecoregion are Lake Tlawi, a high-altitude lake in the Mbulu Highlands, that supports a non-breeding congregation of Fulica cristata, the Rufiji delta that supports thousands of migrant waterbirds, and the Usangu flats along the Ruaha river that supports at least 418 bird species and congregations of Dendrocygna bicolor, Balearica regulorum, and Plectropterus gambensis (Baker & Baker 2001; Baker & Baker 2002). The Rufiji and several of its tributaries run through the large Selous Game Reserve in southeastern Tanzania. With its extensive rivers and streams, this reserve is expected to hold significant numbers of Gorsachius leuconotus, Ephippiorhynchus senegalensis, Scotopelia peli, and Rynchops flavirostris (Baker & Baker 2001).
The extensive marshes, Typha swamp, floodplain grasslands, open water, rice paddies, and man-made lagoons of the Chilwa-Chiuta system also provide habitat for many waterbirds (Dudley et al. 1979). Over 150 species of resident birds and 37 Palaearctic birds have been observed at Chilwa; of these species 22 are regular visitors from September to April (Dudley et al. 1979). The seasonal and long-term changes in lake level have major impacts on floodplain inundation and consequently on waterbird populations. The site holds populations of the vulnerable lesser kestrel (Falco naumanni), and the locally rare pallid harrier (Circus macrourus),and great snipe (Gallinago media).
Aquatic mammals that live in the ecoregion include marsh mongoose (Atilax paludinosus), African clawless otter (Aonyx capensis), and hippopotamus (Hippopotamus amphibius). Dugong (Dugong dugon), listed by IUCN as Vulnerable, can be found in the lower brackish reaches of some rivers in Mozambique, the southern Rufiji delta and perhaps also in southern Tanzania (Hughes & Hughes 1992; IUCN 2002).
Ecological phenomena:
BirdLife has identified Lake Chilwa as an important area for congregations of waterbirds. Significant populations of Egretta ardesiaca, Plegadis falcinellus, Platalea alba, Dendrocygna bicolor, Amaurornis flavirostra, Gallinula angulata, Porphyrio alleni, P. porphyrio, and Rynchops flavirostris have been documented on the floodplains of the lake (Dowsett-Lemaire et al. 2001).
Justification for delineation:
This ecoregion includes coastal basins from the Wami River in Tanzania to the Luala River in Mozambique and includes the Ruaha/Rufiji, Ruvuma, and Lúrio Rivers, as well as other smaller basins. The relatively depauperate freshwater fish fauna of the rivers of this coastal ecoregion has its greatest affinities with the Zambezi fauna (Bills 1997; Lévêque 1997). Many of these rivers may have been dry as recently as the last interpluvial, which accounts for their low species counts (Roberts 1975). The Tanzanian Shield rivers, meaning those rivers between the Athi basin in the Kenyan Coastal Rivers ecoregion [864] to the Zambezi in the Lower Zambezi ecoregion [866], at times converged due to fluctuations in sea level and may account for the similarity in fauna among many of the coastal rivers of the Eastern Coastal ecoregion (Lévêque 1997).
Level of taxonomic exploration:
Poor
References/sources:
Baker, N. E.,Baker, E. M. (2002) "Important Bird Areas in Tanzania: A first inventory". Dar es Salaam, Tanzania. Wildlife Conservation Society of Tanzania.
Baker, N. E.,Baker, E. M. (2001)"Tanzania" In Fishpool, L.D.C.;Evans, M.I. (Ed.). Important bird areas in Africa and associated islands: Priority sites for conservation. (pp. 897-945) Newbury and Cambridge, UK: Pisces Publications and BirdLife International (Birdlife Conservation Series No. 11).
Bills, R. (1997) "Freshwater of the Moebase region and their fish communities. Environmental impact assessment of the proposed TIGEN sands mineral mine, Zambezia Province, Mozambique". Grahamstown, South Africa. Coastal Environmental Services.
Burgess, G. H.,Franz, R. (1989)"Zoogeography of the Antillean Freshwater Fish Fauna" In Woods, C.A.;Sergile, F.E. (Ed.). Biogeograpy of the West Indies: Patterns and Perspectives. (pp. 263-304) Boca Raton, FL, USA: CRC Press.
Burgess, Neil D.,Clarke, G. Philip (2000) Coastal forests of eastern Africa, IUCN Forest Conservation Programme. Gland, Switzerland: IUCN.
Clausnitzer, V. (2001). "Notes on the species diversity of East African Odonata, with a checklist of species" Odonatologica 30(1) 49-66.
Dowsett-Lemaire, F., Dowsett, R. J., et al. (2001)"Malawi" In Fishpool, L.D.C.;Evans, M.I. (Ed.). Important bird areas in Africa and associated islands: Priority sites for conservation. (pp. 539-555) Newbury and Cambridge, UK: Pisces Publications and BirdLife International (Birdlife Conservation Series No. 11).
Dudley, C. O., Stead, D. E., et al. (1979)"Amphibians, reptiles, mammals and birds of Chilwa" In Kalk, M.;McLachlan, A.J.;Howard-Williams, C. (Ed.). Lake Chilwa: Studies of change in a tropical ecosystem, Monographiae Biologicae 35. (pp. 247-273) The Netherlands: Dr. W. Junk.
Hatton, J.,Munguambe, F. (1998) "The biological diversity of Mozambique". Maputo, Mozambique. Ministry for the Coordination of Environmental Affairs.
Hughes, R. H.,Hughes, J. S. (1992). "A directory of African wetlands" Gland, Switzerland, Nairobi, Kenya, and Cambridge, UK: IUCN, UNEP, and WCMC.
Kemp, J., Hatton, J. C., et al. (2000). "East African marine ecoregion: Reconnaissance synthesis report" Tanzania: WWF.
Lévêque, C. (1997) Biodiversity dynamics and conservation: The freshwater fish of tropical Africa. Cambridge, UK: Cambridge University Press.
Lovett, Jon C., Hatton, John, et al. (1997). "Assessment of the impact of the lower Kihansi hydropower project on the forests of Kihansi Gorge, Tanzania" Biodiversity and Conservation 6(7) 915-933.
Manongi, F. J. (1993)"River basin planning and management of wetlands" In Kamukala, G.L.;Crafter, S.A. (Ed.). Wetlands of Tanzania: Proceedings of a seminar on wetlands of Tanzania, Morogoro, Tanzania. Gland, Switzerland: IUCN.
Roberts, T. R. (1975). "Geographical distribution of African freshwater fishes" Zool. J. Linn. Soc. 57 249-319.
Schiøtz, A. (1999) Tree frogs of Africa. Frankfurt, Germany: Edition Chimaira.
Stattersfield, A. J., Crosby, M. J., et al. (1998). "Endemic bird areas of the world: Priorities for biodiversity conservation" Cambridge, UK: BirdLife International.
Tweddle, D. (1983). "The fish and fisheries of Lake Chiuta" Luso: J. Sci. Tech. (Malawi) 4(2) 55-81.
