Ecoregion Description

512: Southern Upper Guinea

Major Habitat Type:

tropical and subtropical coastal rivers

Author:

Ashley Brown and Michele Thieme, Conservation Science Program, WWF-US, Washington, DC

Reviewers:

Christian Lévêque, Centre National de la Recherche Scientifique (CNRS), France

Countries:

Guinea; Ivory Coast; Liberia

Boundaries:

The Southern Upper Guinea ecoregion covers nearly all of Liberia, a portion of southern Guinea and part of western Côte d’Ivoire and is defined by the basins of the Mano, Lofa, St. Paul, St. John, Cestos, and Cavally rivers. The relatively short, partly torrential rivers and streams of this ecoregion support a highly endemic freshwater fish and crab fauna (Hugueny & Lévêque 1994).

Drainages flowing into:

Atlantic Ocean

Main rivers or other water bodies:

Major rivers of the Southern Upper Guinea ecoregion include the Mano, Lofa, St. Paul, St. John, Cestos, and Cavally. 

Topography:

Most rivers of the ecoregion originate in the Wologisi Range in the north or the Nimba Range in the southern highlands (500 to 1,000 m asl) and flow relatively short distances to the ocean. The upper courses of the rivers, which are slowly eroding the plateau region, are rocky and torrential (Lévêque et al. 1990). The relief along the coast is relatively steep and cataracts abound in the courses of the rivers. The Mano River, for example, encounters over 15 waterfalls throughout its lower course (Hughes & Hughes 1992). 

Climate:

The climate of Southern Upper Guinea is hot and humid. The ecoregion receives high levels of rainfall—over 4,000 mm along the coast and about 2,000 mm inland. Rain falls an average of 180 days per year, mainly from April/May to October. River discharges peak in September/October while low levels occur in February/March. Temperatures throughout the ecoregion average 24^o C in the coolest month and 27^o C in the warmest month (Hughes & Hughes 1992).

Freshwater habitats:

There are few floodplains in this ecoregion, though near the mouths of the rivers swamps and mangrove forests occur. 

Terrestrial Habitats:

Historically, the upper and middle reaches of the rivers flowed through moist lowland forests that were evergreen towards the coast and semi-evergreen further inland.

Fish Fauna:

The rivers and streams of Southern Upper Guinea are rich in aquatic fauna, including 151 species of fish. Many fish of Southern Upper Guinea possess adaptations for life in swift rivers with rocky bottoms. Species of the Amphiliidae family, with elongated and humped forms, can resist currents and stay on the river bottom (Welcomme 1985). Amphilius spp. cling to the substrate using stiff pectoral spines and a sucker-like mouth, whereas Chiloglanis spp. and Labeo spp. possess buccal suckers (Lévêque et al. 1990, 1992). 

Description of endemic fishes:

About one-fifth of the 151 fish species are endemic, with high levels of endemism within the Cyprinodontidae, Cyprinidae, and Cichlidae families. 

Other noteworthy fishes:

Some genera recorded in Upper Guinea bioregion are also represented in the Lower Guinea and Congo bioregions but have never been found in between: Doumea, Paramphilius, Microsynodontis, Parailia, Ichthyborus and Caecomastacembelus. Some species are also common to Upper and Lower Guinea and Congo: Mormyrus tapirus, Isichthys henryi, Papyrocranus afer,and Xeosmystus nigri (Lévêque et al. 1990). These occurrences support the view that Upper Guinea was a refuge zone for fish during dry climatic periods. 

Other noteworthy aquatic biotic elements:

Several rare mammal species inhabit Southern Upper Guinea. The vulnerable pygmy hippopotamus (Hexaprotodon liberiensis) survives in some of the remaining forested areas (East 1999). The hippopotamus (Hippopotamus amphibius) and the vulnerable West African manatee (Trichechus senegalensis) also live in the rivers of this ecoregion (IUCN 2002). Several smaller mammals depend on the short, swift rivers for feeding. For example, the African water rat (Colomys goslingi) feeds on aquatic insects, crustaceans, and other invertebrates and the endangered, endemic Mt. Nimba otter shrew (Micropotamogale lamottei) feeds on crabs, fish, and insects in streams (Kingdon 1997; IUCN 2002). 

Habitat partitioning has occurred among the three species of crocodiles that inhabit the ecoregion. Nile crocodiles (Crocodylus niloticus) live in the mangrove swamps and river-mouths. Slender-snouted crocodiles (C. cataphractus) live in larger rivers that run through rain forest, and dwarf crocodiles (Osteolaemus tetraspis) live in forested small streams (Kofron 1992).

Several bird and frog endemics inhabit Southern Upper Guinea. The endangered rufous fishing owl (Scotopelia ussheri) is largely restricted to the rain forests of this ecoregion, although small populations may also survive elsewhere in Côte d’Ivoire (Fry et al. 1988). Eleven of 52 frog species are endemics, with the majority of endemics in the Phrynobatrachus genus. Many Phrynobatrachus species migrate between different habitats to avoid desiccation (Rödel 2000). 

Justification for delineation:

Southern Upper Guinea is part of the Upper Guinea bioregion, which is characterized by a distinct ichthyofauna that includes many endemics. This high endemism is likely the result of long-term geographic isolation and stable and wet climatic regimes. The Guinean range is an impassable barrier to the dispersal of fish from the Upper Guinean streams to Nilo-Sudanian basins. Rapids and waterfalls within individual basins have likely served as additional barriers (Lévêque et al. 1990; Lévêque 1997). Different ecological conditions (forested Upper Guinean streams versus savanna Sudanian streams) also potentially contributed to the species divergence (Hugueny & Lévêque 1994). It is hypothesized that the relatively high endemism may also be due in part to the forested rivers of this ecoregion acting as a “refuge” for aquatic fauna during dry climatic periods (Lévêque 1997).

Level of taxonomic exploration:

Fair

References/sources:

East, R. (1999) Antelopes: Global survey and regional action plans. Gland, Switzerland and Cambridge, UK: IUCN/SSC Antelope Specialist Group.

Fry, C. H., Keith, S., et al. (1988). "The birds of Africa, Volume III" London: Academic Press.

Hughes, R. H.,Hughes, J. S. (1992). "A directory of African wetlands" Gland, Switzerland, Nairobi, Kenya, and Cambridge, UK: IUCN, UNEP, and WCMC.

Hugueny, B.,Lévêque, C. (1994). "Freshwater fish zoogeography in West Africa: Faunal similarities between river basins" Environmental Biology of Fishes 39 365-380.

Kingdon, Jonathan (1997). "The Kingdon field guide to African mammals" San Diego, CA, USA: Academic Press.

Kofron, C. P. (1992). "Status and habitats of the three African crocodiles in Liberia" Journal of Tropical Ecology 8(3) 265-273.

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

Lévêque, C., Paugy, D., et al. (1990) The fresh and brackish water fishes of West Africa, Vol. 1. Paris: ORSTOM-MRAC.

Welcomme, R. L. (1985). "River Fisheries, FAO Fisheries Technical Paper, No. 262" Rome, Italy: FAO.