Ecoregion Description

540: Upper Congo

Major Habitat Type:

tropical and subtropical upland rivers

Author:

Ashley Brown, Conservation Science Program, WWF-US, Washington, DC

Reviewers:

Uli Schliewen, Zoologische Staatssammlung München, Munich,Germany and David Kaeuper, United States Ambassador to the Repub

Countries:

Democratic Republic of Congo

Boundaries:

The Upper Congo ecoregion lies entirely within the Democratic Republic of Congo (DRC) and extends from the base of the Shaba Plateau to the Upper Congo Rapids [539]. 

Drainages flowing into:

Main rivers or other water bodies:

The upper course of the Congo River, called the Lualaba, is a large, slow-flowing river for most of its course, except when broken by the “Portes d’Enfer” (Gates of Hell) rapids in its upper reaches. This ecoregion’s most upstream point occurs where the Luvua River, a tributary to the Lualaba, exits Lake Mweru [806] and flows northwest to meet the Lualaba. At the confluence of the Luvua and Lualaba, the Lualaba River doubles in width and many elongate islands occupy the middle of the channel. About 100 km downstream, the Lukuga River, which drains the overflow from Lake Tanganyika, enters the Lualaba (Bailey 1986). The Lukuga is more heavily mineralized than the Lualaba and Luvua rivers, but small relative discharge has a minor effect on the Lualaba’s water chemisty. Below the Lukuga confluence, the river begins its descent of 135 m over a distance of 880 km, beginning with the “Gates of Hell” at Kongolo, a 50-km series of rapids stretching from Kimbombo to Kindu (Bailey 1986). Here, the gorge narrows to 200 to 600 m wide as the river flows over the rapids. Below these rapids, the river broadens to 2 to 3 km and swells with inputs from the Elila, Ulindi, and Lowa tributaries, each descending from eastern highlands and together contributing between 2,000 and 5,000 m³ per second of water (Bailey 1986; Hughes & Hughes 1992). The upper course of the Lomami River, which joins the mainstem Congo further downstream in the Cuvette Centrale [537], drains a substantial area within this ecoregion. Similarly, the Lindi River is largely contained within this ecoregion but its confluence with the Congo is technically within the Cuvette Centrale ecoregion [537]. 

Topography:

The Lualaba in this ecoregion starts at an elevation of about 800 m asl and flows northwards through savanna into the central equatorial plain, where it gradually descends to the Upper Congo Rapids [861] at about 500 m asl (Marlier 1973; Bailey 1986; Library of Congress 1993).

Climate:

he climate of the ecoregion is tropical and very wet, especially near the equator. Rainfall increases along the length of the Lualaba as it flows north towards the equator. Rainfall is 1,400 mm per year near Kasonga, shortly downstream of where the Luama joins the Lualaba.  It increases to 1,700 mm per year further north near Kindu, and increases to over 2,000 mm per year approaching Kisangani. There is no distinct dry season in this region. October is the wettest month, and December, January, and February are the driest. Temperatures vary little, and mean annual temperature for most of the Democratic Republic of Congo is 24^o C (Hughes & Hughes 1992).

Freshwater habitats:

The Lualaba experiences a bimodal flood regime in its northern reaches near the equator.  However, some tributaries remain unimodal, including the Elilia and the Ulindi Rivers. The Lowa is irregular, tending towards bimodality with maxima occurring from April to May and again from November to December (Marlier 1973). Riverine forests and swamps border the slow-flowing reaches (Hughes & Hughes 1992). 

Terrestrial Habitats:

The terrestrial landscape through which the Lualaba flows undergoes a transition from savanna in the south to high equatorial forest in the north. Acacia caffra is common in riparian vegetation, and Nymphaea spp. lives in open waters. The Lualaba is lined by Cyperus papyrus and Typha domingensis, as well as Pycreus mundtii and Paspalidium geminatum. Aeschynomene elaphroxylon and Hibiscus diversifolius comprise areas of swamp woodland (Hughes & Hughes 1992).

Fish Fauna:

The alternating rapids and slow-flowing waters of the Upper Congo support a rich aquatic fauna, despite the low primary productivity of some areas. Over 150 fish species and 6 endemics are known from this ecoregion. It is likely that new surveys in this ecoregion would reveal new species and more endemics. Dominant families include Alestiidae, Cyprinidae, and Cichlidae. 

Description of endemic fishes:

Three cyprinid barbs (Barbus marmoratus, B. nigrifilis, B. papilio), one claroteid catfish (Amarginops platus), kneriiids (Parakneria thysi), one mochokid catfish (Chiloglanis marlieri), and a cichlid (Tylochromis elongatus) are considered endemic.

Other noteworthy aquatic biotic elements:

The ecoregion has an extremely rich mollusc fauna, with 42 species recorded, 22 of which are endemic. Most of the endemic species are from the Thiaridae family. Members of the genus Cleopatra usually can be found in small, slow-flowing or stagnant water bodies. Lanistes nsendweensis is found among rocks beneath falls as well as in forest streams (Brown 1994). 

Bird species present in the ecoregion include the Goliath heron (Ardea goliath) and the pink-backed pelican (Pelecanus rufescens) (Hughes & Hughes 1992). The ecoregion also hosts a rich mammalian and herpetofauna. The aquatic genet, Osbornictis piscivora, is poorly known but is confined to the Congo Basin (Kingdon 1997). Other wetland mammals include Hippopotamus amphibius and several species of otters (Aonyx capensis, A. congicus, and Lutra maculicollis).  Two species of crocodile, the Nile crocodile (Crocodylus niloticus) and the slender-snouted crocodile (C. cataphractus), are also present (Riley & Huchzermeyer 1999). Over 30 species of frogs are known from the ecoregion with three of these being endemic or near-endemic (Hyperolius diaphanus, H. frontalis, and Afrana amieti).

Justification for delineation:

This ecoregion extends from the outlet of Lake Mweru downstream to the Upper Congo Rapids ecoregion [539] and is distinguished by an endemic mollusc fauna and believed to harbor a largely undescribed endemic fish fauna. Because rapids isolate the upper Congo fish fauna from the rest of the Congo River system, many fish species of the Cuvette Centrale [537] are not found in the Upper Congo (Banister 1986; Lévêque 1997). Several fish of the Nilo-Sudanian bioregion occur in the upper Lualaba that are not found in the main Congo River channel, as they are confined by the rapids at Portes d’Enfer. These species include Polypterus bichir, Ctenopoma muriei, Oreochromis niloticus, and Ichthyborus besse (Beadle 1981). Debate continues over the origin of these Sudanian species in the upper Lualaba (Lévêque 1997). The upper Lualaba also shares a substantial number of species with the Zambezi River (Poll 1976; Lévêque 1997).

Level of taxonomic exploration:

Poor. Surveys have not been conducted in this ecoregion in many years such that recent data is lacking. Much historic data on fish and aquatic invertebrates remain uncatalogued.

References/sources:

Bailey, R. G. (1986)"The Zaire River system" In Davies, B.R.;Walker, K.F. (Ed.). The ecology of river systems. (pp. 201-214) Dordrecht, The Netherlands: Dr W. Junk Publishers.

Banister, K. E. (1986)"Fish of the Zaire system" In Davies, B.R.;Walker, K.F. (Ed.). Ecology of river systems. (pp. 215-224) Dordrecht, The Netherlands: Dr W. Junk Publishers.

Beadle, L. C. (1981). "The inland waters of tropical Africa" England: Longman Group Limited.

Brown, David (1994). "Freshwater snails of Africa and their medical importance" London, UK: Taylor & Francis.

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.

Lévêque, C. (1997) Biodiversity dynamics and conservation: The freshwater fish of tropical Africa. Cambridge, UK: Cambridge University Press.

Library of, Congress (1993) "Country studies: Zaire" <http://lcweb2.loc.gov/frd/cs/kmtoc.html#km0006>(2001)

Marlier, G. (1973)"Limnology of the Congo and Amazon rivers" In Meggers, B.J.;Ayensu, E.S.;Duckworth, W.D. (Ed.). Tropical forest ecosystems in Africa and South America: A comparative review. (pp. 223-238) Washington, DC, USA: Smithsonian Institution Press.

Poll, M. (1976). "Poissons.Exploration du Parc National de l’Upemba" Fondation pour favoriser les Recherches Scientifiques en Afrique 73 1-127.

Riley, J.,Huchzermeyer, F. W. (1999). "African dwarf crocodiles in the Likouala swamp forests of the Congo basin: habitat, density, and nesting" Copeia 199(2) 313-320.