Malagarasi - Moyowosi
Luc De Vos, National Museum of Kenya, Nairobi, Kenya
Major Habitat Type
Tropical and subtropical floodplain rivers and wetland complexes
Drainages flowing into
Main rivers to other water bodies
Three major rivers — the Malagarasi, Moyowosi, and Ugalla — flow onto the plateau and form the extensive swamps of this ecoregion. The Malagarasi, which flows onto the plateau from the northwest, has its headwaters in the hills (elevation about 1800 m) adjacent to Lake Tanganyika on the Burundi/Tanzania border. The Moyowosi River and its tributaries flow from the north and east. The Ugalla River, the main tributary to the Malagarasi, originates in the south of the ecoregion. The Malagarasi and the Ugalla are each about 500 km long and the Moyowosi is about 200 km long (De Vos & Seegers 1998).
Productive swamps cover large areas of the Malagarasi-Moyowosi ecoregion, which includes the Malagarasi river basin above Uvinza and the headwaters of the Rugufu and Luiche Rivers. These rivers and their tributaries flow onto a central plateau (1,000-2,000 m) and eventually drain into Lake Tanganyika . The majority of the ecoregion falls within northwest Tanzania and a small section extends into southeastern Burundi.
The Malagarasi drainage includes a large variety of biotopes, including swampy areas; small and medium-sized river channels with different bottom types and water chemistries; a large, slowly flowing large river with a few moderate rapids; and a large delta divided into two major branches (De Vos & Seegers 1998). On the upper Malagarasi and its headwaters, at altitudes of about 1,200 to 1,250 m asl, strips of permanent swamp intermittently line both banks. There is also a large swamp stretching from where the Nikonga and Kigosi Rivers meet the Moyowosi, continuing to where the Moyowosi joins the Malagarasi. The gradient of the Moyowosi River and its tributaries decreases as they reach the plateau, causing them to overflow their banks and divide into multiple channels. This permanent swamp zone is about 160 km long and up to 36 km in width, with an area of about 3,200 km2. During the wet season, about 2,500 km2 of inundated floodplain occurs on two tributaries of the Moyowosi, the Kigosi and Gombe Rivers. There are also about 1,800 km2 of floodplains and permanent swamps on the Ugalla River and its tributaries, the Ziuwe and the Wala (Hughes & Hughes 1992).
Vegetation varies with biotope. Papyrus (Cyperus papyrus) dominates the swamp vegetation, with Typha, Carex and other emergent vegetation also present. Grasses, such as Oryza spp. and Echinochloa pyramidalis, occur on the seasonal floodplains. Within the water column, species from the genera Potamogeton, Ceratophyllum, Chara, and Utricularia are common. Water lilies, water chestnut (Trapa), water fern (Azolla), and the Nile cabbage (Pistia) are also present (Beadle 1981).
On lands surrounding seasonal floodplains, Brachystegia spiciformis-Julbernardia globiflora miombo-woodland grows. Brachystegia microphylla is dominant on granitic outcrops present in the area (Institute of Resource Assessment 2002). Gallery forests with species such as Acacia spp., Borassus aethiopum, and Phoenix reclinata also occur along the headwater streams (Beadle 1981; Hughes & Hughes 1992).
Description of endemic fishes
Despite many connections to the Lake Rukwa system, nearly 15 per cent of the Malagarasi fishes are endemic to the system. The vast majority of endemics belong to the Cichlidae family, particularly to the riverine mouth-brooding goby cichlids of the genus Orthochromis. This genus has undergone a species radiation on the east side of the ecoregion, where it is represented by at least 8 species (De Vos & Seegers 1998). Orthochromis species are also found in drainages to the west of Lake Tanganyika (Congo drainage), which again indicates old contacts between the two systems. Other endemic Malagarasi cichlids belong to the genera Haplochromis, Oreochromis, and Serranochromis. Further endemic species belong to the catfish genera Clariallabes and Chiloglanis; the killifishes Aplocheilichthys and Nothobranchius; the cyprinids Opsaridium and Barbus; and the spiny eels Mastacembelus.
Other noteworthy fishes
Two lungfish species (family Protopteridae), fishes that have accessory organs for surviving periods of low oxygen, occur within the swamps of this ecoregion.
Justification for delineation
This ecoregion is defined by the Malagarasi-Moyowosi basin. The entire Malagarasi catchment drains an area of 130,000 km2 and includes the area from the mountains bordering Tanzania and Burundi through to the Malagarasi-Moyowosi swamps (Patterson & Makin 1998). The Malagarasi catchment composes about 30% of the Lake Tanganyika drainage basin, and the Malagarasi is Lake Tanganyika\'s largest affluent (De Vos & Seegers 1998). Two smaller affluents, the Luiche and Rugufu Rivers, also drain into Lake Tanganyika in Tanzania. The Malagarasi is flanked by these rivers, with the Luiche entering Lake Tanganyika about 30 km to the north and the Rugufu entering about 14 km to the south. Several shared ichthyofaunal elements suggest that these rivers were connected formerly with the Malagarasi, forming the Proto-Malagarasi (De Vos & Seegers 1998). Due to their shared ichthyofauna with the Malagarasi the headwaters of the Luiche and Rugufu Rivers are included within this ecoregion.
Level of taxonomic exploration
- Baker, N. E.;Baker, E. M. (2002) \Important Bird Areas in Tanzania: A first inventory\ (Dar es Salaam, Tanzania)
- Beadle, L. C. (1981). "The inland waters of tropical Africa" England: Longman Group Limited.
- De Vos, L. and Seegers, L. (1998). "Seven new Orthochromis species (Teleostei: Cichlidae) from the Malagarasi, Luiche and Rugufu basins (Lake Tanganyika drainage), with notes on their reproductive biology" Ichthyological Exploration of Freshwaters 9 pp. 371-420.
- De Vos, L., Seegers, L., Taverne, L., et al. (2001). "L'ichtyofaunde du bassin de la Malagarasi (système du lac Tanganyika): Une synthèse de la connaissance actuelle" Annls. Mus. r. Afr. Centr. (Zool.) 285 pp. 117-152.
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- Institute of Resource Assessment (2002) \Baseline Study of Lakes Sagara and Nyamangoma Wetlands and the surrounding Environment in the Malagarasi / Muyovozi Ramsar Site, Western Tanzania. Final Report prepared by: Institute of Resource Assessment (IRA) University of Dar es Salaam\ Dar es Salaam, Tanzania. Ministry of Natural Resources and Tourism - SIMMORS.
- Patterson, G. and Makin, J. (1998). The state of biodiversity in Lake Tanganyika: A literature review Chatham, UK: Natural Resources Institute.
- Seegers, L. (1996). "The fishes of the Lake Rukwa drainage, Annales du Musée royal de l’Afrique Central, Sciences Zoologiques, 287" Tervuren, Belgium:
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- Wetlands International (2002) \Ramsar Sites Database: A directory of wetlands of international importance\ "<"http://ramsar.wetlands.org/">" (2003)