Egg banks in dryland wetlands provide information on the diversity and vulnerability of branchiopod communities along a longitudinal aridity gradient

Continued degradation of temporary wetlands and rapidly declining freshwater biodiversity call for identification of vulnerable species as targets for conservation and management efforts. Branchiopod crustaceans are endemic to temporary waters and rely on banks of drought-resistant eggs in the sediment for survival across dry seasons. These egg banks are like archives to biologists and allow them to estimate population status and resilience, without the need to sample active communities. Such an approach has, however, not yet been fully explored. Here, we investigate egg bank abundance and morpho-species richness to assess the vulnerability of branchiopod communities in dryland landscapes. For study systems, we use 98 temporary wetlands across the Northern Cape Province, South Africa, which contained eggs of Notostraca, Anostraca, Spinicaudata and Cladocera. We invoked the insurance hypothesis to investigate community resilience and studied egg bank abundance to reveal population status. Our results indicate that branchiopod communities become more vulnerable along an aridity gradient, from the semi-arid eastern regions to the arid western parts of the province. Apart from longitude, we also considered a suite of other environmental descriptors to explain variability in egg bank abundance and richness patterns and found that egg bank abundance decreased with alkalinity.