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Invertebrate Resistance to Wetland Drying

Strachan, Scott (2016) Invertebrate Resistance to Wetland Drying. PhD thesis, Murdoch University.

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In regions with a drying climate, as waterbodies dry out more frequently or for longer, species traits interact with aquatic habitat influencing assemblage composition in wetlands. This thesis aimed to identify potential refuges from increased temperatures and altered water regimes for wetland invertebrates that resist drying using resting stages in the sediment. Using the literature on desiccation-responses by freshwater invertebrates, I reviewed relationships between life histories and the degree of desiccation to which individuals are exposed. Sediment microhabitats that retain moisture were sampled, showing that they could provide microrefuges for invertebrates during seasonal drying. Dry sediment was sampled from two habitats (open water (OW) and fringing trees (FT)) in eight wetlands, sediment properties were measured, and invertebrate emergence from inundated damp and artificially dried sediment were observed. FT sediment was cooler, had higher organic matter content, water saturation potential and different invertebrate assemblage composition. For most species the effect of drying depended on habitat; effects included mortality, reduced abundance and increased abundance. False starts occur when dry wetlands receive brief, unseasonable periods of inundation that trigger invertebrate hatching, but then dry out causing abortive hatching. OW and FT sediments were exposed to false starts in the laboratory. In OW, abortive hatching occurred and new assemblages emerged from egg banks during the next inundation. In FT, invertebrates emerged rapidly and survived drying, continuing to develop into assemblages that did not differ from permanently inundated controls. Overall, this research showed that shallow seasonal wetlands contain refuges from higher temperatures and prolonged drying, explaining the resistance of their fauna to drought. To sustain wetland biodiversity, FT vegetation should be protected and replanted (where necessary) and wetland sediment should be protected from degrading processes such as sedimentation and eutrophication, so that it retains microrefuges.

Item Type: Thesis (PhD)
Murdoch Affiliation(s): School of Veterinary and Life Sciences
Supervisor(s): Robson, Belinda, Chester, Edwin and Chambers, Jane
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