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).

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). 

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.

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. 

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