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Ecoregion Description


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Species Richness


# of Endemic Species


Threats

527: Western Red Sea Drainages

Major Habitat Type:

xeric freshwaters and endorheic (closed) basins

Author:

Abebe Getahun, Department of Biology, Addis Ababa University, Addis Ababa, Ethiopia

Countries:

Djibouti; Egypt; Egypt, Administered by Sudan; Eritrea; Ethiopia; Sudan

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.

Main rivers or other water bodies:

The only perennial river in the ecoregion is the Awash River, which arises in central Ethiopia, crosses the rift valley, and drains into Lake Abhe. The lakes in this region include Lakes Abhe, Afambo, Afdera, Asale, Bario, and Gamari. There are hot springs flowing into some of the lakes (e.g., Lake Afdera). Lakes Abhe, Afambo, Bario, and Gamari are adjacent to one another and interconnected, since they are the ending for the Awash River; whereas Lakes Afdera and Asale are located further north in the Dallol depression.

Topography:

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

Climate:

Dry conditions prevail over the Red Sea coast and rainfall is extremely variable both in quantity and in timing. Occasionally cyclonic storms of Mediterranean origin enter the Red Sea, and their effects are felt in the east of the ecoregion along the coast. These storms originate when relatively cold air from the highlands meets warmer air over the Red Sea. On the coastal plains maximum rainfall occurs in December-February, and the annual rainfall is less than 300 mm (Westphal 1975). Mean temperatures for the hottest months are 30-35oC, and the humidity is high (Orme 1996).

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.

Fish Fauna:

Due to the high salinity of the inland lakes within this ecoregion, the fauna that inhabit them are adapted to both fresh and salt waters (e.g., the cichlid fish Danakilia franchettii). There are also hot springs flowing into Lake Afdera. Water from the hot springs dilutes the salinity of the lake, and most of the fish inhabit the area at the junction of the lake and the hot springs.

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).

Other noteworthy aquatic biotic elements:

Large numbers of Palearctic migrant birds visit the woody vegetation around Lake Abhe and adjacent lakes. The site is believed to hold more than 20,000 waterbirds annually. Some of these birds are white-faced tree duck (Dendrocygna viduata), white pelican (Pelecanus onocrotalus), squacco heron (Ardeola ralloides), cattle egret (Bubulcus ibis), little egret (Egretta garzetta), and marabou (Leptoptilos crumeniferus). Many Palearctic species also visit the site as an important staging point on their migration route to and from the Arabian Peninsula, both in autumn and in spring, including Basra reed warbler (Acrocephalus griseldis) (Ethiopian Wildlife and Natural History Society 1996, 2001). About 16,000 non-breeding Phoenicopterus ruber and 600 P. minor have been observed on the Djibouti side of the lake (Magin 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).

References/sources:

Getahun, A. (1998)"The Red Sea as an extension of the Indian Ocean" In Sherman, K.;Okemwa, E.N.;Ntiba, M.J. (Ed.). Large marine ecosystems of the Indian Ocean: Assessment, sustainability, and management. (pp. 277-281) Cambridge, MA, USA: Blackwell Science.

Getahun, A.,Lazara, K. J. (2001). "Lebias stiassnyae: A new species of killifish from Lake Afdera, Ethiopia (Teleostei: Cyprinodontidae)" Copeia 1 150-153.

Magin, G. (2001)"Djibouti" In Fishpool, L.D.C.;Evans, M.I. (Ed.). Important bird areas in Africa and associated islands: Priority sites for conservation. (pp. 233-239) Newbury and Cambridge, UK: Pisces Publications and Birdlife International.

Orme, A. R. (1996)"Coastal environments" In Adams, W.M.;Goudie, A.S.;Orme, A.R. (Ed.). The physical geography of Africa. (pp. 238-266) Oxford, UK: Oxford University Press.

Trewavas, E. (1983). "Tilapiine fishes of the genera Sarotherodon, Oreochromis and Danakilia" London: British Museum (Natural History).

Westphal, E. (1975). "Agriculture systems in Ethiopia. Joint publication of the College of Agriculture, Haile Selassie I University, Ethiopia and the Agricultural University, Wageningen, The Netherlands"

Williams, M. A. J., Bishop, P. M., et al. (1977). "Late quaternary lake levels in southern Afar and the adjacent Ethiopian Rift" Nature 267 690-693.

Wood, C. A.,Lovett, R. (1979). "Rainfall reliability in Ethiopia, Tables and maps" SINET: Ethiopian Journal of Science 2 111-120.

Wood, R. B.,Talling, J. F. (1988). "Chemical and algal relationships in a salinity series of Ethiopian inland waters" Hydrobiologia 158 29-67.

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