IUCN is working closely with a range of partner organisations to undertake species assessments, and to extend the range of species represented on the IUCN Red List. One such group is freshwater crabs, which have been assessed through the Sampled Red List Index project coordinated by the Zoological Society of London (ZSL) and are contributing to the Pan Africa assessment project.
Almost one fifth of the world’s crabs are restricted to freshwater, a total of 1,281 species. Overlooked in comparison to their more speciose marine counterparts, they are distributed throughout almost all freshwater habitats in tropical regions. Traits such as low reproductive output in combination with fragmentation caused of human impact to freshwater habitats has resulted in relatively high threat levels in this group that is defined by high levels of endemism. A total of 32% of freshwater crabs in non Data Deficient categories are threatened with extinction. The exact threat level is unknown, as the status of 629 Data Deficient species is undetermined, but ranges between 16% (assuming no Data Deficient species threatened) and 65% (assuming all Data Deficient species threatened).
The majority of the threatened species have highly restricted ranges. This exposes them to the impacts of human disturbance from habitat loss, particularly in forested regions, with alteration of water regimes and pollution being most frequently cited as cause of threat.