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Ecoregion Description
551: Cuanza
Major Habitat Type:
tropical and subtropical coastal rivers
Author:
Lucy Scott, South African Institute for Aquatic Biodiversity, Grahamstown, South Africa
Reviewers:
Paul Skelton, South African Institute for Aquatic Biodiversity, Grahamstown, South Africa
Countries:
Angola
Boundaries:
All the westward flowing rivers of Angola lie within this ecoregion. The coastal and escarpment rivers of western Angola contain a poorly known freshwater fauna that is suspected to be rich in species and to have a high number of endemics.
Drainages flowing into:
Atlantic Ocean
Main rivers or other water bodies:
The principal drainages, from north to south, are the M\'bridge, Loje, Dende, Bengo, Cuanza (Quanza), Cuvo, and Catumbela Rivers.
Topography:
This region covers a narrow coastal plain and a stepped escarpment rising to an altitude of over 1,000 m (Hughes & Hughes 1992).
Climate:
Precipitation increases from an annual average of 500 mm along the coast in central Angola to about 1000 mm in the central interior. The Benguela Current influences and reduces rainfall along the semi-arid coast. Temperatures remain relatively stable year-round with a mean annual temperature of about 20-22°C, although the average is higher in the coastal lowlands (Hughes & Hughes 1992).
Freshwater habitats:
The Cuanza River, over 970 km long, with its major tributaries the Lucala and the Luando, has the largest catchment (about 146,000 km2) of all the rivers in this ecoregion. As the river descends below the 1,000 m contour, it begins to develop a series of extensive swamps. Near the junction of the Luando and Cuanza Rivers is a large floodplain with tracts of permanent swamp and floodplains occur sporadically downstream from here until Dondo. Wetland vegetation includes Cyperus papyrus, Typha capensis, Phragmites mauritianus, and Echinochloa stagnina. Lakes and lagoon then occur adjacent to the river until it meets the Altantic Ocean, where there are extensive mangroves (Hughes & Hughes 1992; Dean 2001).
Terrestrial Habitats:
Cloud forests on the escarpment appear to be in part a southern extension of the central African rainforests as well as having distinct Afro-montane affinities. Inland, on the plateau, vegetation is predominantly miombo (Brachystegia / Julbernardia) woodland, containing an extensive network of grassy dambos. Dense gallery forests line the major watercourses. Rapids or falls occur in the mainstem of all of the large rivers throughout their descent down the western escarpment of Angola (Roberts 1975). Coastal savanna is the predominant vegetation on the coastal belt, although thicket is more common in the north (Stuart et al. 1990).
Fish Fauna:
Although the area is poorly known, richness and endemism among fish (and potentially other groups) is suspected to be high. No recent accounts are available and knowledge is based mainly on collections made by early expeditions (Nichols & Boulton 1927; Fowler 1930; Trewavas 1936; Ladiges 1964). At least 14 families of freshwater fish are represented in the ecoregion (Roberts 1975). Poll (1967) records about 109 freshwater fishes of which 40% percent are cyprinids and 17% cichlids (Poll 1967; Roberts 1975).
Description of endemic fishes:
Possibly as many as thirty endemics (27%) are known from this ecoregion but the real status is difficult to ascertain given the lack of comparative information from neighboring tributaries of the Congo and the Angolan reaches of the Cunene and the Okavango (e.g., see Greenwood 1984)(Greenwood P. H. 1984).
Other noteworthy aquatic biotic elements:
Aquatic frogs are relatively abundant in this ecoregion’s wetlands with over fifty species known, including the endemics Cuanza reed frog (Hyperolius punctulatus), H. cinereus, Bufo grandisonae, Congulu forest tree frog (Leptopelis jordani), Quissange forest tree frog (L. marginatus), and Rana parkeriana. Further studies would also expect to reveal new species and endemics.
Several wetlands and floodplains in the ecoregion hold congregations of waterbirds that occur in numbers that are at least nationally significant. These include Quiçama, Mussulo, and the Luando Strict Nature Reserve. Among the waterbirds found at these Important Bird Areas are the globally threatened Grus carunculatus and Phoenicopterus minor (Dean 2001). In addition, there are about twenty aquatic molluscs known from the waters of this ecoregion. About one-quarter of these species are shared with those of the Lower Congo ecoregion [822].
Several aquatic-obligate mammals are known from the rivers and streams of this ecoregion, including the West African manatee (Trichechus senegalensis), giant otter shrew (Potamogale velox), and the African water rat (Colomys goslingi) (Kingdon 1997).
Justification for delineation:
The fish faunas of the rivers of this ecoregion are poorly known, however, it appears that they have greater affinity with the fauna of the Southern West Coastal Equatorial bioregion than with the Congo or Zambezi bioregions. The Cuanza ecoregion is considered its own distinct bioregion because the Zambezian fauna is absent or poorly represented and there are a number of endemic species described (Trewavas 1936, 1973; Roberts 1975). The Cichlidae and a number species from other families in the upper Cuanza River are related to species from the Zambezi and Cunene River basins (Trewavas 1973). The earlier Vernay Angola Expedition (Nichols & Boulton 1927) and Gray African Expedition (Fowler 1930) also record a number of species from the upper reaches that are distinctly Zambezian, thus, the upper Cuanza basin has been included in the Zambezian Headwaters ecoregion [555].
Level of taxonomic exploration:
Poor. This is a critical ecoregion for major collection effort and study, as it is very little known scientifically. The faunas and ecological functioning of the aquatic systems in the region are in need of investigation, and a significant amount of further study is needed before the degree of biological distinctiveness can be determined in this area.
References/sources:
Dean, W. R. J. (2001)"Angola" In Fishpool, L.D.C.;Evans, M.I. (Ed.). Important bird areas in African and associated islands: Priority sites for conservation. (pp. 71-91) Newbury and Cambridge, UK: Pisces Publications and Birdlife International.
Fowler, H. W. (1930). "The fresh-water fishes obtained by the Gray African Expedition 1929. With notes on other species in the Academy collection" Proceedings of The Academy of Natural Sciences of Philadelphia 82 27-83.
Greenwood, P. H. (1984). "The haplochmine species (Teleostei, Cichlidae) of the Cunene and certain other Angolan rivers" Bulletin of the British Museum (Natural History) 47(4) 187-239.
Hughes, R. H.,Hughes, J. S. (1992). "A directory of African wetlands" Gland, Switzerland, Nairobi, Kenya, and Cambridge, UK: IUCN, UNEP, and WCMC.
Kingdon, Jonathan (1997). "The Kingdon field guide to African mammals" San Diego, CA, USA: Academic Press.
Ladiges, W. (1964). "Beiträge zur zoogeographie und oekologie der süsswasserfische Angolas" Mitt. Hamburg Zool. Mus. Inst. 61 221-272.
Nichols, J. T.,Boulton, R. (1927). "Three new minnows of the genus Barbus, and a new characin from the Vernay Angola Expedition" American Museum Novitates 264 1-8.
Poll, M. (1967). "Contribution à la faune ichthyologique de l´Angola" Lisbon: Diamang.
Roberts, T. R. (1975). "Geographical distribution of African freshwater fishes" Zool. J. Linn. Soc. 57 249-319.
Stuart, S. N., Adams, R. J., et al. (1990) Biodiversity in Sub-Saharan Africa and its islands: Conservation, management and sustainable use, Occasional Papers of the IUCN Species Survival Commission No. 6. Gland, Switzerland: IUCN.
Trewavas, E. (1973). "A new species of cichlid fish of rivers Quanza and Bengo, Angola, with a list of the known Cichlidae of these rivers and a note on Pseudocrenilabrus natalensis" Fowler. Bull. Br. Mus. Nat. Hist. (Zool.) 25 27-38.
Trewavas, E. (1936). "Dr Karl Jordan’s expedition to South-West Africa and Angola: The freshwater fishes" Novitates Zoologicae 40 63-74.
