Salinisation of arid temporary pools alters crustacean hatching success but not phenology dynamics.

Abstract

The widespread acceleration of freshwater salinisation due to human activities, such as pollution, resource extraction and urbanisation coupled with climate change, poses a significant threat to aquatic ecosystems. Limited work has been directed towards salinisation effects in temporary wetland systems. These systems are characterised by unique crustacean communities reliant on dormant egg production. We assessed salinisation effects on temporarywetland crustacean communities from semi–arid pans in the Khakhea–Bray Transboundary Aquifer region of South Africa using a laboratory–based approach. Sediment from pans containing crustacean resting eggs was exposed to water with varying salinities (0‒10 ppt), and emergent hatchlings were assessed over a 30–day hydroperiod. At salinities of 2.5 ppt and above, there were significant decreases in emergent taxa richness and abundance. Spinicaudata and Ostracoda were the most sensitive taxa to high salinities. Cladocera, Copepoda, Notostraca and Anostraca hatchlings had shallower decreases with salinity, but hatchability still fell rapidly. There was a limited effect on community hatching phenology dynamics from salinity, with all taxa showing reduced hatchability over time overall, with the exception of Cladocera which exhibited a clear unimodal response, peaking around 20 days post‒inundation. This suggests that the main impact of salinisation in these systems will be reductions in hatching success and hence reduced recruitment, leading to changes in predation pressures, food web structure and functioning of these ecosystems, with implications for associated ecosystem services.