River basins containing the highest species richness across the five taxonomic groups (freshwater fish, molluscs, aquatic plants, dragonflies and freshwater crabs) were identified by mapping species distributions to create the corresponding distribution maps. A small number of Data Deficient species could not be mapped and were, therefore, excluded from the analysis.
The most important areas that can be highlighted as having the highest numbers of freshwater assessed species are: The Middle and High Atlas, and the Riff mountains to the northeastern lowlands and estuaries of Morocco ( 67% of the dragonflies found in the region, 56% of the aquatic plants, 24% of the freshwater molluscs, 6% of the fish and 33% of the crabs), Subtropical Numidia at the eastern Mediterranean coast of Algeria and Tunisia, including the surrounding areas from Kabylia to Kroumirie (63% of the dragonflies, 51% of the aquatic plants, 33% of the crabs, 15% of the freshwater molluscs and 5% of the fishes), and the Nile River basin in Egypt, predominantly the Lower Nile (67% of the crabs, 34% of the dragonflies, 33% of the aquatic plants, 24% of the molluscs and 24% of freshwater fish).
Distribution of river basins according to the level of biodiversity they contain in fish, molluscs, odonata, aquatic plants and freshwater crabs
On the western side of the Mediterranean basin, the Mediterranean and Northern Atlantic coasts of Morocco, as well as the Riff and parts of the High and Middle Atlas Mountains, are the most important areas in terms of the number of freshwater threatened species present (53% of the regionally threatened freshwater taxa are present). More to the east, the areas that reach a similar level of species richness are the east of Algeria (Numidia), and the north of Tunisia (Kroumirie, north of the Medjerda river) (25% of the threatened taxa), in addition to the Egyptian Nile River Basin (13% of the threatened taxa) on the eastern side of the region, with Lake Nasser just downstream (that is located outside the study region).
Distribution map showing concentrations of threatened species of the fish, molluscs, odonates and aquatic plants taxonomic groups
Most northern African endemic species are located in the Middle and High Atlas and, generally to a lower degree, in the Betico-Rifan arc in Morocco, the Kabylia–Numidia region in Algeria and the Kroumiria Mountains in Tunisia (54% of the freshwater species endemic to the northern Africa region are present in these areas together).
Distribution map showing areas of high endemicity of the fish, molluscs, odonates, aquatic plants and freshwater crabs
The River Nile basin stands out for being the region where more northern African species have gone extinct. In total, 28 species have been recorded as Extinct or Regionally Extinct in this area, including 23 freshwater fish, 3 odonata and 2 molluscs.
Distribution map showing areas of high number of Extinct or Regional Extinct species of freshwater fish, molluscs and odonates