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

Abstract

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.

Wetlands in drylands: diverse perspectives for dynamic landscapes

“…This disparity was accredited to the shorter hydroperiod and simpler geomorphology of the treed swamps which reduced species replacement during the periods in which branchiopods and insects were dominant. The overall effect, as in the study by Meyer-Milne et al (2022), is a reduction in biodiversity with aridity. In extreme cases of prolonged drought, it is possible that these systems may even become terrestrialised (cf., Sandi et al 2019), with permanent loss of wetlands.…”

“…For instance, in their study of branchiopod communities in temporary wetlands of South Africa, Meyer-Milne et al ( 2022 ) found that fewer branchiopod eggs were stored in wetland soil sub-surface layers as aridity increased. This suggests that although egg and seed stores might provide an opportunity for species to survive droughts, sustained increases in aridity as a consequence of climate change may exceed species resilience.…”

“…Potentially, therefore, these types of studies could contribute to the design of restoration interventions for ecosystem service provision. Studies of wetland edaphic conditions (Van Huyssteen and Johnson 2022), vegetation succession (Rebelo et al 2022) and the use of biota as indicators of ecosystem processes and stressors (Marconi et al 2022;Meyer-Milne et al 2022;Timms 2022) are equally valuable in ensuring that restoration strategies address drivers of change and promote natural recovery in abiotic-biotic linkages. The inclusion of traditional ecological knowledge (Moggridge et al 2022) is viewed as a critical practical strategy for strengthening the effectiveness of ecological restoration and promulgating a global restorative culture to achieve the ideals of the United Nations "Decade on Ecosystem Restoration" (2021-2030) (Aronson et al 2020).…”