North Africa Freshwater Molluscs

Freshwater habitats and biodiversity are recognized to be under serious threat at global level. Monitoring freshwater basins is therefore important to prevent the loss of these ecosystems and freshwater mollusc species have been identified as one of the priority taxa indicators for the overall conservation status of wetland ecosystems.

A total of 155 North African freshwater and brackish molluscs have been assessed in the two distinct biogeographic areas: the Palearctic northern African region (also called “Maghrebian-Egyptian region”) and the Afrotropical northern African region. In total, 118 and 51 mollusc species are native to the Maghrebian-Egyptian and the Afrotropical regions respectively. Although many taxa were excluded from the assessment for taxonomic uncertainty, molluscs here included provide a good picture of molluscan biodiversity across the region.

The Siwa Oasis in Egypt

Conservation status

Among the 155 freshwater molluscs species evaluated, 42.5% are threatened with extinction, with 17.4% classified as Critically Endangered, 19.4% as Endangered and 8.4% as Vulnerable. Almost a quarter of these species (22.6%) has been classified as Least Concern, and 17% as Data Deficient. There are 17 species considered as Regionally Extinct in North Africa, with 15 endemic to the region. Analyzing separately the Palearctic and Afrotropical freshwater molluscan conservation status, the percentage of threatened species differs dramatically, with the former having values quite higher than the latter (55.8% and 7.7% respectively). In addition, the classification as “Data Deficient” differs in biogeographic regions; whereas in the Afrotropical region a species so classified might still be present but the lack of data makes its taxonomic status doubtful, in the Palearctic region some of the species so classified are only known from the original 19th century description, with their current presence and range unknown.
 

The number of mollusc species in each Red List category in the northern African region

Species richness

Palearctic region
In the Palearctic region the highest number of species is recorded in the Middle Atlas (39%). The species richness shows in fact a gradual decline from the west to the east, the richest community occurring in the region of Atlantic meseta and mountains, which receives the highest level of water precipitation. The causes of this decline are clearly linked to anthropogenic factors such as pollution and overexploitation of surface and ground waters. The comparison between the distribution pattern of the total species richness and the species richness of threatened species does not show marked differences in this part of the region. The number of the species considered or to go extinct is most likely underestimated here, as many Data Deficient and Critically Endangered species may also be extinct by now.

Afrotropical region

In the Afrotropical region the highest species richness is found in the Egyptian Nile where 39 species are present. Beyond the borders of the Nile, the Sahara begins and the species richness decreases to fewer taxa, and never more than 5. The number of threatened species in this region is very low, as low is the amount of Data Deficient cases. Only a single species (Chambardia letourneuxi) results to be extinct, with the causes of this extinction unknown.
 

Distribution of all, threatened and andemic taxa.

Endemic species

The number of endemic species in the Palearctic area of North Africa is quite high. The Atlantic and Mediterranean region in the Maghreb has revealed to be a true malacological hotspot with a surprisingly high quantity of endemic molluscs both in surface and in underground waters. Here the number of species with restricted ranges in surface waters has its highest level in the Moroccan rivers running towards the Atlantic. On the contrary, the amount of endemism in the Afrotropical part of North Africa is quite low, with only one species (Gyraulus ehrenbergi) in the Egyptian Nile system.
 

Main threats

The main threats to the conservation of freshwater molluscs in North Africa are the increasing periods of droughts, water abstraction, pollution, salinization of freshwater, molluscicides (confined to Egypt), habitat loss due to the construction of physical barriers, and species collection.

  • The overuse of underground waters has resulted in a rise of underlying saline waters and a decrease of freshwater levels. This phenomenon is particularly severe in Maghreb, being this region unique for the diversity of subterranean mud snails, and in Libyan Arab Jamahiriya where the whole shallow coastal aquifer has now become saline. Moreover, pollution due to industrial and urban agglomerations affects both Maghrebian surface and underground waters.
  • The erection of dams, on the other hand, doesn’t appear to adversely affect North African mollusc species. The Egyptian Nile freshwater malacofauna seems to be even positively impacted by the Aswan Dam as it regulates the water volume and diminishes the sediment carried by the river. However, a future problem caused by the Dam may be the shrinkage of the Delta, as consequence of the erosion.
  • The introduction of alien species does not seem to constitute a threat to indigenous species, though extinction by over-collecting may pose a threat in synergy with other dangers, particularly if collectors’ interests in freshwater molluscs keep rising. 

Water pollution in wetland areas as a result of detergents used for washing clothes (Morocco)

Water pollution in wetland areas as a result of detergents used for washing clothes (Morocco)

Photo: Laila Rhazi

Conclusions and conservation measures

  • The present IUCN study has revealed that the species richness of north-western Africa has been severely underestimated. A large number of species are on the verge of extinction and further research is needed to ascertain the status of all species.
  • Freshwater resources in the region are being severely depleted and both surface and ground waters are being polluted. Increasing aridity and global warming is strongly aggravating the already severe human impact on the aquatic ecosystem.
  • A separate discussion must be done in Egypt for the Nile, where the molluscan populations seem to be in good condition, having extended their range over the whole river thanks to the decrease of water velocity since the building of the Aswan Dam.
  • The most urgent conservation recommendations are the inventory of species of freshwater populations in Maghrebian countries, the protection of the quality and quantity of aquifers (particularly of those still relatively unpolluted headwaters in the Atlas rivers), the protection of coastal wetlands, and a complete ban for the introduction of non-indigenous molluscivore fish.

A team of Moroccan and Spanish malacologists aided by local youngsters collecting Margaritifera marocana in the Oued Abid (Morocco). After tissue
samples were taken, the animals of the last viable population of this species were placed back