Boundaries

One perennial river, several temporary rivers, isolated oases, and saline lakes are among the few water bodies in the xeric, depauperate Sahara. Less than 100 mm of rain falls each year in much of this desert-covered ecoregion, which extends from the northwestern coast of Egypt, across Libya and Algeria through the northern portions of Mali and Mauritania, and ends at the Atlantic Coast in Western Sahara (Morocco) (Hughes & Hughes 1992). The Sahara encompasses much of the Sahara Desert and includes the southern portion of the Atlas Mountains.

Freshwater habitats

Oueds or wadis, defined as stream beds that are usually dry but flow periodically during the rainy season, drain the mountains of the Sahara. This ecoregion contains the Oued Saoura, the largest temporary river of the Sahara and an extension of the Oued Guir system, which originates in the Moroccan Atlas and flows southeast. During large floods, it has been reported that the Oued Saoura will flow some 500-700 km into the desert (Hughes and Hughes 1992). In the extreme west of the ecoregion there are no permanent streams and drainage courses are almost always dry (Dumont 1987). Temporary watercourses of note in the west include the Oued Draa, Oued Rheris, Oued Guier, and Oued Sassaf. Ephemeral streams also drain the highlands of the southern tip of Tunisia, flowing toward chotts (shallow irregularly flooded depressions) in the north. These watercourses include the Wadi al Farigh, Wadi al Hamin, and Wadi ash Shu’bah. Pools that are left behind when rivers stop flowing are called gueltas. The Gueltas of Ziza are located in the center of the ecoregion and include a one inside a volcanic crater. These gueltas receive their water from the oueds of the Ziza Mountains (Hughes and Hughes 1992). Three gueltas, Issakarassene, Afilal and Vallée d’Ihierir, are Ramsar sites in Algeria.

Numerous temporary pans, pools, sebkhets, and chotts are also scattered across the ecoregion, and are especially prevalent near the coast where rainfall is higher. A sebkhet (or sebkha, sabkhat) is a large, shallow depression that holds water seasonally, though sometimes for over a year. Unlike sebkhets, chotts are irregularly flooded and may not be flooded every year (Davies & Gasse 1987). Large western sebhkets include Sebhket Agsumal in Western Sahara (Morocco) and Sebkha Iquetti, Sebhka Oumm Ed Drous Telli, and Sebkha Oumm Ed Drouse Guebli in Mauritania. In the center of the ecoregion in Algeria lie the Tidihelt Depression, which includes Sebkha Azzel Matti, Sebkha Mekerrhane and numerous chotts. Many chotts, oases, and semi-permanent lakes dot the landscape in the east. Near the coast in Libya lie two large sebkhets, Sabkhat Al Ghuzayytt and Sabkhat al Qunayy. In Egypt, the Siwa Depression contains about a dozen lakes on its floor. These lakes fluctuate seasonally and sometimes dry up. The nearby Qattara Depression also contains four semi-permanent saline lakes (Hughes and Hughes 1992). 

Several subterranean basins occur beneath the Sahara Desert. Water from rainfall quickly seeps down through porous rock, filling the renewable underground aquifers (Beadle 1981). Artesian wells take advantage of these waters. The Nubian Sandstone Aquifer, a nonrenewable resource (i.e., fossil water or ancient reserves of underground water), covers an area greater than 2.5 million km² and underlies most of Egypt, Eastern Libya, northern Sudan, and northern Chad. The rate of total extraction from the Nubian Sandstone Aquifer is about 1,030 Mm³/yr in Egypt, 850 Mm³/yr in Libya, and 405 Mm³/yr in Sudan (Centre for Environment and Development for the Arab Region and Europe 2001).

Much of the aquatic vegetation in the ecoregion is halophytic. Plants from the halophytic Chenopodiaceae and Saliciornicaceae families line the saline sebkhats and Halocnemum strobilaceum is the most common plant in the saline chotts (Hughes and Hughes 1992). In western Algeria, Halopeplis amplexicaulis is a pioneer plant often found on the salt banks of inland lakes (Tremblin 2000). Salt pans in the north of Libya support halophytic Juncus, Limonium, Salicornia, Sarcocornia, and Suaeda. Phragmites australis, Typha capensis, and Cynodon dactylon all grow along the Oued Saoura. In the central portion of Algeria, filamentous green algae as well as stands of Typha capensis and less often Phragmites australis grow in gueltas. Oases support species that grow directly in pools and swamps, such as Juncus spp., Phragmites australis, Ceratophyllum demersum, and Potamogeton spp. Chara sp., a stiff, attached macrophyte, grows in the Siwa and Quattra Depression lakes (Hughes and Hughes 1992). Two oases at Adrar, Algeria, Ouled Saïd and Tamentit, support more than one hundred varieties of date palm (Phoenix dactylifera) (Boumezbeur 2002).

Terrestrial habitats

Overall, richness of the aquatic fauna of the Sahara is low, although fish richness and endemism are both relatively high considering the scarcity of permanent water bodies. There are about 40 fish species known from this ecoregion, about 20 of which are endemic. 

The fish species that inhabit the waters of this ecoregion are adapted to the range of habitats and temperature extremes of its waters. The cooler waters of the mountains support Cobitidae and Salmonidae, families whose distributions are generally found in more northern latitudes. Cobitis maroccana is a short-lived species that occurs in watercourses with little current, and Salmo trutta is a coldwater species (FishBase 2001). At the other extreme, within the alkaline chotts that experience high temperature variability, species from the Lebias genus are probably the only permanent residents (Roberts 1975). The eggs of Lebias fasciatus are able to develop in the absence of water, in the sand or humid mud (LeBerre 1989).

Justification for delineation

This ecoregion follows Doadrio (1994)(Doadrio 1994) in extending the Maghreb ichthyofaunal province southward to include the desert regions up to the Ahaggar Mountains. The freshwater fauna of this ecoregion contains elements of both Palearctic (i.e. the fish families Cobitidae, Salmonidae) and Afro-tropical origin, and the two ecoregions together form their own bioregion. However, the ephemeral nature of the waters of this ecoregion has led to the survival of fewer species than in the neighboring ecoregion. The ecoregion is delimited by the Atlas Mountains in the north and the Ahaggar Mountains in the south.

Level of taxonomic exploration

Good