North Africa Freshwater Crabs

Although poor in water resources, the North Africa region shows a good representation of aquatic and wetlands habitat and monitoring freshwater basins is important to prevent the loss of these ecosystems. Freshwater carb species have been identified as one of the priority taxa indicators for the overall conservation status of wetland ecosystems.

The North Africa region from Morocco to Egypt is home to three species of crabs belonging to two different families: Potamidae and Potamonautidae. The Potamidae is the largest of all freshwater crab families, and the only North Africa representative of this group is the Algerian River Crab (Potamon algeriense), found in the temperate rivers of Maghreb and in seasonally freshwater bodies. The Potamonautidae is a predominantly Afrotropical family present in North Africa with two species: the Nile River Crab (Potamonautes niloticus) and Berard’s River Crab (Potamonautes berardi), inhabiting and never leaving the Nile River system. Although the low crab species richness and diversity reported in North Africa is based on a large number of specimens’ records, further research is necessary to better understand the actual distribution of these species.

Conservation status

All three species of freshwater crabs in North Africa are found in more than one country and are classified as Least Concern, only one (Potamon algeriense) being endemic to the region.

The number of crab species in each regional Red List Category in the northern African region

Case Studies

Algerian River Crab (Potamon algeriense)

Algerian River Crab’s distribution includes Morocco, Algeria and Tunisia, being the only species endemic to the Maghreb of North Africa. The species can also be found at high altitudes in the Middle Atlas, a region rich in water resources originating rivers that drain into the Mediterranean Sea and the Atlantic Ocean. Although present population levels are estimated to be stable, the geographical distribution appears to be discontinuous and fragmented and may be cause of concern for the future stability of some isolated subpopulations. Water diversion, drainage, habitat disturbance and pollution are the main threats affecting populations near centres of human concentration.

Nile River Crab (Potamonautes niloticus)

It is a large river crab endemic to the Nile River basin completely dependent on aquatic habitats. The species never leaves the water and it has never been found outside the Nile system, occurring in the River itself and in its major channels, lowland tributaries, and in the lakes associated with the basin. Although benefitting from wide distribution, an estimated stable population size, and lacking known widespread threats, crab populations may be under threat from rapid anthropogenic changes in the future.

Berard’s River Crab (Potamonautes berardi)

The species is quite common although its distribution is strictly limited to the Nile River basin. It is in fact widely distributed throughout the river and its tributaries in Egypt and further to the South. Its wide distribution and the estimated stability of its population size, made it to be listed as a not threatened species. In spite of this, although widespread threats to the species are actually not known, crab populations may be under threat from rapid anthropogenic changes in the future and could also suffer from over-harvesting in Lake Victoria.

 

The three freshwater crab species inhabiting North African basins: Potamon algeriense, Potamonautes niloticus, Potamonautes berardi

Species richness

Of the three species assessed in this study, only one occurs exclusively in North Africa (Algerian River Crab’s), being the other two on the northern end of a wider distributional range that extends into Egypt. The taxonomy diversity of the region is lower than that of the Mediterranean region as a whole (12 species), and lower than the whole of the rest of continental Africa (120 species) and Madagascar (14 species). Although this fact is due to the low availability of permanent surface water in the region (as the number of species here found is considered typical of such arid ecosystems), further exploration is needed throughout North Africa. Until now, no species of freshwater crabs are known to have gone extinct (Extinct or Extinct in Wild).
 

Distribution map of the freshwater crabs P. bernardi, P. niloticus and P. algeriensis in the northern African
region.

Main threats

Threats to crabs in North Africa freshwater ecosystems include habitat destruction driven by increasing agriculture and industrial development, the alteration of fast flowing rivers for the creation of hydroelectric power plants, and the drainage of wetlands for farming and other uses. Excessive water abstraction and sedimentation associated with farming activities are also decreasing habitat quality. The appropriate management of water resources in the future should ensure the survival of these species.
 

Conclusions and conservation recommendations

  • The region’s freshwater crab fauna does not appear to be in immediate trouble when compared with other assessed freshwater groups of the region, such as fish, molluscs, and dragonflies. These species have in fact proved to be relatively tolerant to changes in land-use affecting freshwater ecosystems. However, even species assessed as not threatened could suffer catastrophic declines.
  • Significant areas of the region remain insufficiently explored. There is a need for surveys to refine species distribution, define specific habitat requirements, describe population levels and trends, and identify specific threats to North Africa’s freshwater crab fauna.
  • Further sampling efforts may also lead to the discovery of other crab freshwater species inhabiting the region.

Students from the Sciences Faculty of the Cadi Ayad University studying the biodiversity of a stream in Morocco (educational ecoservice).