Motivation 10• Climate change is prolonging dry periods in intermittent rivers and wetlands in many regions across the world, 11increasing the potential for desiccation stress in the fauna. Invertebrates comprise the greatest proportion of 12 biodiversity in these systems, but there are no recent reviews on the response of invertebrates to desiccation in the 13context of climate change. 14• This review elaborates on the idea that the degree of desiccation that fauna experience is likely to be critical for 18• This review uses pre-electronic era literature which often includes detailed observations of species behavioural 19 responses to drying, but which has often been ignored in more recent studies. Also, it brings together this pre-20 electronic era literature with contemporary ideas of species traits and how they affect ecology. 21• Confusion in the terminology used to describe species' responses to desiccation is currently a barrier to coherent

Summary Seasonally intermittent freshwater environments show large temporal changes in area andenvironmental conditions (which may be harsh). We investigated whether microhabitats that retain moisture could provide a refuge during drying in a seasonal wetland.2. We investigated occupancy by invertebrates of three potential microrefuge types: surface depressions, shallow cracks and deeper fissures in the sediment of a wetland in Western Australia. Our aims were to determine whether the assemblages occupying these microrefuges differed and whether they changed as the wetland dried and reflooded.3. Ten microrefuges of each type were sampled for invertebrates, sediment and temperature during each of three hydrological phases: the damp phase (surface waterabsent but sediment moist), the dry phase (groundwater at its lowest level) and the reflooded phase (surface water present). Sediment samples taken from each microrefuge in the damp and dry phases were reflooded in the laboratory to reveal species aestivating or present as eggs, and sediment organic matter content was measured.4. Sediment organic matter content did not change between wetland phases. The invertebrate assemblage in the microrefuges showed almost complete species turnover between phases.Invertebrate composition differed between microrefuges, and temperature in the deeper fissures was on average > 10 °C lower than in surface depressions and shallow cracks.5. Microcrustaceans and gastropods survived the drier months as resting stages in the microrefuges and either emerged or hatched from eggs upon reflooding. Several species, including isopods and caddisflies, were collected only from cracks and fissures as the wetland dried. During drying, a high diversity of carnivorous species was observed in the microrefuges. Sediment microrefuges apparently underpin resistance to drought by invertebrates in SouthLake. Those species that depend on sediment fissures to survive may be threatened by declining the groundwater table in the region. Changes to wetland hydrology and other human activities that affect wetland sediment or vegetation will affect the range of microrefuges available to invertebrates to survive drying, and may thus alter wetland biodiversity.

In dry climate zones, headwater streams are often regulated for water extraction causing intermittency in perennial streams and prolonged drying in intermittent streams. Regulation thereby reduces aquatic habitat downstream of weirs that also form barriers to migration by stream fauna. Environmental flow releases may restore streamflow in rivers, but are rarely applied to headwaters. We sampled fish and crayfish in four regulated headwater streams before and after the release of summer-autumn environmental flows, and in four nearby unregulated streams, to determine whether their abundances increased in response to flow releases. Historical data of fish and crayfish occurrence spanning a 30 year period was compared with contemporary data (electrofishing surveys, Victoria Range, Australia; summer 2008 to summer 2010) to assess the longer–term effects of regulation and drought. Although fish were recorded in regulated streams before 1996, they were not recorded in the present study upstream or downstream of weirs despite recent flow releases. Crayfish (Geocharax sp. nov. 1) remained in the regulated streams throughout the study, but did not become more abundant in response to flow releases. In contrast, native fish (Gadopsis marmoratus, Galaxias oliros, Galaxias maculatus) and crayfish remained present in unregulated streams, despite prolonged drought conditions during 2006–2010, and the assemblages of each of these streams remained essentially unchanged over the 30 year period. Flow release volumes may have been too small or have operated for an insufficient time to allow fish to recolonise regulated streams. Barriers to dispersal may also be preventing recolonisation. Indefinite continuation of annual flow releases, that prevent the unnatural cessation of flow caused by weirs, may eventually facilitate upstream movement of fish and crayfish in regulated channels; but other human–made dispersal barriers downstream need to be identified and ameliorated, to allow native fish to fulfil their life cycles in these headwater streams.

Habitat alters the effect of false starts on seasonal-wetland invertebrates. 2. A laboratory emergence experiment was used to determine whether the abortive hatching caused by false starts alters assemblage composition in the subsequent hydroperiod; and whether the length of the dry period following a false start alters subsequent assemblage composition. Sediment for the experiment was collected from Lake Joondalup South, Swan Coastal Plain (SCP), Western Australia, because it has a relatively diverse assemblage of desiccation-resistant invertebrate propagules. Most wetlands on the SCP are seasonal and groundwater-fed and the region has a mediterranean-type climate 3. Two different habitat types (open water (OW) and fringing trees (FT)) with distinct freshwater invertebrate assemblages are commonly found in SCP wetlands. We repeated the experiment in sediment from both habitats to determine whether false starts had the same effect on the two assemblages. Replicate sediment samples from both habitats were placed in microcosms randomly allocated to treatments or controls.To simulate false starts of differing dry-period duration, treatments were inundated for five days, then allowed to dry out for different time periods (10, 20, 30 days) then inundated for five days. Controls were inundated for time periods equivalent to the total duration of each false start treatment (20, 30, 40 days). 4. FT sediment had higher organic matter and moisture content than OW sediment. The composition of the emerging assemblage differed between habitats, and emergence was slower from OW than FT sediment. Abortive hatching followed the false start in OW sediment, but subsequently the same assemblage emerged, showing reliance on the egg bank to re-supply lost populations. Abortive hatching was not observed in FT sediment, where invertebrates survived drying during the false start, continuing to develop for up to 30 d without surface water, because those sediments retained moisture.5. Provided that winter-spring hydroperiods continue to inundate OW for several months, these results indicate that invertebrates will be able to complete their life cycles and replenish egg banks following abortive hatching, demonstrating resilience to false starts. False starts to winter inundation rarely occur more than a month prior to the start of 'true' winter rains, so FT assemblages are resistant to false starts, showing the ability to survive dry periods of up to 30 days. Furthermore, survival in damp FT sediment also gave these populations a 'head start', because the surviving assemblage was identical to the continuously inundated control. 6.Assemblages emerging from beneath FT may potentially recolonise inundated OW habitat. So far, changes to SCP seasonal-wetland hydroperiods will be within the coping range of their invertebrate assemblages. As FT assemblages were more resistant to false starts, restoration schemes that increase shading by fringing vegetation should be encouraged.

Climate change is causing prolonged drying in many seasonal wetlands, including urban wetlands, potentially affecting aquatic invertebrates that take refuge in wetland sediment during dry periods and thereby threatening wetland biodiversity. We collected sediment from two habitats: open water (OW) and fringing trees (FT), in eight urban wetlands after seasonal inundation had ended. Both habitats are inundated during winter-spring and dry in summer-autumn. Each sediment sample was divided into subsamples. One set of subsamples were inundated in the laboratory to test the hypothesis that emerging invertebrate assemblages would differ between OW and FT sediments. Another set of subsamples was dried, stored for a year, and inundated to test the hypothesis that prolonged drying would reduce the abundance and taxa richness of emerging invertebrates. The composition of emerging invertebrate assemblages differed between habitats, with more amphibious species found in FT sediment. Invertebrate responses to prolonged drying and storage varied among species: for some, effects depended on habitat type, while others delayed emergence or showed no response. Microcrustacean abundance was unaffected by drying, suggesting that their productivity during refilling may resist drier water regimes. Surface temperatures of dry sediment are cooler beneath FT, and this sediment has higher organic matter, holds more water and is less dense than OW sediment; and FT sediment remained cooler than OW sediment in the laboratory, despite the absence of shading. Fringing trees may therefore provide a refuge for some freshwater invertebrates relying on dormant stages in the sediment to survive drying in urban wetlands.