Boundaries

This ecoregion is delineated based on the basins of the coastal lakes that occur along the Red Sea from the Gulf of Tadjoura at the border with the Horn ecoregion [883] north to the Nile Delta [524]. The ecoregion extends as a narrow strip along the shore of the Red Sea from Egypt to Djibouti for some 2,000 km. The lowest depression on earth (the Dallol depression) is found in this ecoregion. The depression extends from about 80 m to 160 m below sea level (Wood & Talling 1988). The ecoregion is xeric and experiences high air and water temperatures, to which the fauna are adapted, and includes fresh, brackish, and saline waters.

Topography

The plain is low and flat, but the topographic monotony is interrupted by a number of dry riverbeds and isolated hills.

Freshwater habitats

Lake Abhe, located at 240 m above sea level on the border between Ethiopia and Djibouti, is at the terminus of the Awash River. It is the largest of the lakes in the ecoregion, covering a surface area of 350 km². It is a saline lake (160 g per liter) of moderate depth (maximum depth 37 m).

Lake Afdera, located 12.6oN and 41oE at an altitude of 80 meters below sea level, sits within a depression that currently experiences volcanic and tectonic activities (Williams et al. 1977). Hot springs flow into the lake and are the only source of water other than scanty precipitation. Average annual rainfall is only about 100mm (Wood & Lovett 1979). This saline lake has a surface area of 70 km² and a maximum depth of about 80 m (Wood & Talling 1988). The midday air, lake, and spring water temperatures in November have been recorded at 40oC, 33oC, and 50oC, respectively (Getahun & Lazara 2001). Unlike the other southern saline lakes in Ethiopia (Lakes Abiata, Shala, Chitu and Metahara), the pH of Lake Afdera is low and in the acidic range.

Lake Asale is found at an altitude of 155 m below sea level. The surface area is 55 km². The maximum depth is 40 m, and the salinity is high (276.5 g per liter). Located only 10 km from the Red Sea and at an altitude of 155 m below sea level, the lake receives seawater through seepage. The predominance of chloride in Lake Asale creates an extremely high salinity. No data are available as to its biodiversity.

Description of endemic fishes

Although little studied, these lakes are suspected to host a few endemic fishes. For example, in Lake Afdera there is one endemic monotypic fish genus, Danakilia franchettii (Trewavas 1983), and one endemic species, Lebias stiassnyae (Getahun & Lazara 2001).

Justification for delineation

The coastal lakes of this ecoregion are believed to have been formed as an extension of the Red Sea, and hence the fauna is more related to that of the Red Sea and the Mediterranean than to the southern lakes of the Rift Valley. The fish fauna is of marine origin. Lebias dispar, which is common in Lake Afdera, for example, is found in the Red Sea and the Mediterranean. Danakilia franchetti from Lake Afdera is also believed to be closely related to a species, Iranocichla hormuzensis, on the Arabian Peninsula in southwestern Iran (Trewavas 1983).

Level of taxonomic exploration

Poor. Very little is known about this ecoregion in general and about the saline lakes and their fauna, in particular. Except for sporadic sampling, there have not been any thorough ecological or biological studies of the lakes in this ecoregion. The endemic fishes from Lake Afdera were collected from a small segment (about 100 m² area) at the shore where one of the hot springs joins the lake. It is not known whether these fishes live in the pelagic zone or along the shores where other springs join the lake. The exact number of springs joining the lake is not also known. Although Lake Afdera is reported to be biologically unproductive (Wood & Talling 1988), no mention has been made as to the extent of its life forms (microbial, phytoplankton, zooplankton, and others).