Do Inter‐Basin Water Transfer Schemes Facilitate the Dispersal of Freshwater Crabs Across Catchments? A Genetic Case Study From the Eastern Cape, South Africa

The impacts of inter‐basin water transfer schemes (IBWTs) are well‐understood globally. In South Africa, changes caused by the connection of the Orange, Great Fish and Sundays rivers have been studied, but evidence of inter‐basin dispersal is restricted to freshwater fishes. This study investigated whether IBWTs provided conduits for the dispersal of freshwater crabs (genus Potamonautes ) across catchment divisions.

Crabs were sampled from ten locations, representing upstream, putatively native populations from the three catchments and downstream (potential recipient) populations. Mitochondrial DNA sequence data (from the protein‐coding cytochrome c oxidase subunit I and non‐coding 16S rRNA regions) and microsatellite genotype data were analysed to identify catchment‐specific lineages and potentially admixed populations, indicating movement among catchments.

Genetically distinct populations of Potamonautes were identified in each catchment, and there was no evidence of admixture or catchment‐lineage discordance to suggest translocation or gene flow among catchments.

These results show a lack of inter‐basin dispersal and indicate that human‐made connections do not facilitate crab dispersal. In contrast, ecological differences, such as habitat preferences and feeding ecology, may predispose other groups, such as certain freshwater fishes, to migrate through these connections.

This study highlights the importance of understanding species‐specific responses when evaluating the potential impact of IBWT schemes, and underscores the need for further research on the movement ecology of African freshwater crabs.