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Ecoregion Description
515: Ashanti
Major Habitat Type:
tropical and subtropical coastal rivers
Author:
Ashley Brown and Michele Thieme, WWF-US, Conservation Science Program, Washington, DC, USA
Reviewers:
Christian Lévêque, Centre National de la Recherche Scientifique (CNRS), Paris, France
Countries:
Ghana; Ivory Coast
Boundaries:
This ecoregion is located in Ghana’s previously forested southwestern corner and a small portion of Côte d’Ivoire’s southeast.
Drainages flowing into:
Atlantic Ocean
Main rivers or other water bodies:
From west to east, the main rivers of the ecoregion are the Bia, Tano, Ankobra, and Pra (called the Ofin in its upper course). The lower course of the Tano River inundates 75 km2 of forested swamps before flowing into the Aby lagoon complex (Hughes & Hughes 1992). The Bia River also feeds into this complex. Lake Bosumtwi (38.5 km2), an endorheic crater lake created by a meteor impact approximately one million years ago, lies in the northeastern corner of the ecoregion (John 1986; Turner et al. 1996).
Climate:
In this tropical, wet ecoregion, the length of the rainy season varies along the coast. In the west, near Axim, the rainy season lasts for most of the year and only August is dry, whereas in the east it is bimodal. Precipitation averages about 2,125 mm per year in the west and decreases moving east, from 1,625 mm per year at Cape Three Points to less than 800 mm at the eastern edge of the coast. The primary rainy season east of Cape. Three points lasts from March to July, with rain continuing to a lesser degree from October to November (Hughes & Hughes 1992). Mean temperatures along the coast in the southeastern portion of the ecoregion average about 24o C in the coolest month and 27 o C in the warmest month. Evaporation in the ecoregion can be extremely high, at 1,630 mm per year near Axim and increasing to 2,058 mm in the east (Hughes & Hughes 1992).
Freshwater habitats:
The relatively short rivers of this ecoregion descend gradually from historically forested lowlands into coastal lagoons and swamps.
Terrestrial Habitats:
Moving from north to south, semi-deciduous, moist evergreen, and wet evergreen rainforest forms the natural vegetation, but these now occur in patches due to clearance for agriculture. Along the coast, mangroves line river mouths, especially in the southwestern half of the ecoregion (Hughes & Hughes 1992; Sayer et al. 1992).
Fish Fauna:
The fish fauna is comprised of characids, cichlids, cyprinids, rivulines, and mormyrids; bagrid, mochokid, and clariid catfishes; and a few freshwater pipefish and clupeids. About ten percent of the 105 fish species in the ecoregion are endemic.
Description of endemic fishes:
There are several fish with highly restricted distributions within the ecoregion. Endemic cichlids such as Chromidotilapia bosumtwensis live only in Lake Bosumtwi (FishBase 2001), while Limbochromis robertsi is only known from the Pra River. The spiny eel, Aethiomastacembelus praensis, is restricted to the upper reaches of the Pra River (Teugels et al. 1988).
Other noteworthy aquatic biotic elements:
Several endemic frogs live in or along the forested and mangrove-lined streams of this coastal ecoregion. Fourteen percent of the 55 frog species are also endemic. Most endemic frog species are from the Phrynobatrachus genus. This ecoregion is particularly rich in molluscs, with twenty-one species present, although none are endemic.
Along the coast and in the north of the ecoregion several wetlands serve as breeding and resting grounds for waterbirds. In the Owabi Wildlife Sanctuary in the north, duck species such as Anas querquedula can be found in large numbers, especially during times of drought in Sahelian wintering grounds (Wetlands International 2002). Other aquatic birds present in this sanctuary include jacanas (Jacanidae), pygmy geese (Nettapus auritus), goliath herons (Ardea goliath), and several species of herons (Ardeidae). Approximately 23,000 waterbirds from 27 species inhabit the Muni lagoon in the southeast (Wetlands International 2002).
Justification for delineation:
This ecoregion is defined by the previously forested Ashanti region of Ghana, which probably, with the Eburneo ecoregion [514], remained during dry climatic phases and acted as an aquatic refuge (Hugueny & Lévêque 1994). The fish fauna of this ecoregion is primarily Nilo-Sudanian, with a portion of the fauna of limited distribution to the Ashanti and Eburneo [514] ecoregions. Examples of such species include Marcusenius furcidens, Citharinus eburneensis, and Synodontis bastiani.
Level of taxonomic exploration:
Good
References/sources:
FishBase (2001) "Search FishBase" <http://www.fishbase.org/search.cfm>(2001)
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.
John, D. M. (1986). "The inland waters of tropical West Africa" Stuttgart, Germany: E. Schweizerbart'sche Verlagsbuchhandlung.
Sayer, J. A., Harcourt, C. S., et al. (1992) The conservation atlas of tropical forests: Africa. London, UK: IUCN.
Teugels, G. G., Lévêque, C., et al. (1988). "Etat des connaissances sur la faune ichtyologique des bassins côtieres de Côte d'Ivoire et de l’Ouest du Ghana" Revue d’Hydrobiologie Tropicale 21 221-37.
Turner, B. F., Gardner, L. R., et al. (1996). "The geochemistry of Lake Bosumtwi, a hydrologically closed basin in the humid zone of tropical Ghana" Limnology and Oceanography 41(7) 1415-1424.
Wetlands, International (2002) "Ramsar Sites Database: A directory of wetlands of international importance" <http://www.wetlands.org/RDB/Ramsar_Dir/_COUNTRIES.htm>(2003)
