Increasing salinity drastically reduces hatching success of crustaceans from depression wetlands of the semi-arid Eastern Cape Karoo region, South Africa

Abstract

Salinity is an important factor affecting freshwater aquatic species distribution and diversity. The semi-arid Eastern Cape Karoo region of South Africa has been earmarked for shale gas development through hydraulic fracturing. The process uses large amounts of water and produces briny wastewater. When not managed properly, these wastewaters may lead to salinisation of surface freshwater bodies in the region. Therefore, the effect of salinity on the hatching success of crustacean resting eggs was examined using sediments from four depression wetlands found in the region. The sediments were exposed for 28 days to salinity levels of 0.5 g L−1, 2.5 g L−1, 5 g L−1 and 10 g L−1. Control aquaria in which no salt was added were also set up. There was a significant decrease in the emerged taxa richness and abundances at salinities of 2.5 g L−1 and above. Anostraca, Notostraca and Spinicaudata hatchlings were abundant at salinities of 0.5 g L−1 and below, while Copepoda, Daphniidae (Cladocera) and Ostracoda were observed in the highest salinity, but their densities were still lower with increased salinities. Given the importance of large branchiopods in the trophic balance of depression wetlands, their loss may alter the ecological balance and function of these ecosystems.

Combined impacts of warming and salinisation on trophic interactions and mortality of a specialist ephemeral wetland predator

“…Our laboratory results show that mortality rates of adult L. raynerae increased sharply at salinities of 10 ppt or above. Previous research has demonstrated that hatching success of ephemeral pond specialists, and particularly branchiopods, is considerably reduced at salinity levels above 2.5 ppt (Mabidi et al., ) as a result of hatching cue inhibition or direct toxicity to salt in temporary wetlands (Nielsen et al., ; Vanschoenwinkel et al., ). Indeed, whilst some crustaceans continued to emerge at a salinity of 5 ppt, Mabidi et al.…”

“…Indeed, whilst some crustaceans continued to emerge at a salinity of 5 ppt, Mabidi et al. () demonstrated negligible hatching rates for copepod and branchiopod crustaceans at a salinity of 10 ppt. Thus, our results align with those of Mabidi et al.…”

“…Wetlands are highly biodiverse and productive ecosystems, yet are under increasing pressure from global environmental change via multiple stressors that often act synergistically (Dalu, Wasserman, & Dalu, ; Mabidi, Bird, & Perissinotto, ; White, Donohue, Emmerson, & O'Connor, ). From a biodiversity perspective, ephemeral wetlands are especially important habitats, characteristically inhabited by a rich array of specialists adapted to transient hydroperiods and that may be unable to persist in permanent aquatic ecosystems (Dalu, Wasserman, & Dalu, ; Wasserman, Alexander, Barrios‐O'Neill, Weyl, & Dalu, ).…”

“…The integrity of ephemeral wetlands is thus threatened in multiple ways, such as through land use changes driven by agricultural activity (Brock, Smith, & Jarman, ; Marty, ), species introductions (Cuthbert, Dalu, Wasserman, Dick, et al., ; Dalu, Wasserman, & Dalu, ), and climate change (Lu et al., ). Warming and salinisation are amongst the most pervasive stressors in ephemeral wetlands associated with ongoing environmental change (Dalu, Wasserman, & Dalu, ; Mabidi et al., ). Quantifying the ecological implications of these stressors is key to holistically understanding impacts arising from anthropogenic activity on the functioning and stability of these widespread aquatic habitats.…”

“…Whilst the relative contributions of different environmental cues for dormant egg hatchability remain unclear, salinity has been identified as a particularly important determinant (Brock, Nielsen, & Crossle, ; Skinner, Sheldon, & Walker, ). Indeed, high salinity levels can completely inhibit hatching (Mabidi et al., ; Waterkeyn et al., ) and affect juvenile development (Cancela da Fonseca et al., ; Hart et al., ). Specifically, high salinities may block cues which trigger emergence, or drive mortality through direct toxicity (Nielsen et al., ; Vanschoenwinkel, Seaman, & Brendonck, ).…”