Search

Climate change is altering hydrologic regimes globally. In the Mediterranean climate region of south-western Australia (SWA), climate drying has caused many perennial streams to switch to intermittent flow regimes. Shifts in flow regime are expected to alter physical and biological processes in streams, including litter decomposition, which is the basis of detrital food webs. Decomposition of jarrah (Eucalyptus marginata) leaves and associated macroinvertebrates, were measured over 320 days in 2018–19 using leaf bags in four headwater streams in SWA. Two streams retained perennial reaches and two were formerly perennial streams that are now intermittent. Pre-planned comparisons that formed a partial multiple before–after, control–impact design were used to compare the results to an experiment conducted in 1982–83 in some of the same streams when all were perennially flowing. Both experiments used coarse and fine-mesh bags containing 10 g of dry leaves. In one perennial stream, coarse bags lost more weight than fine bags at the last sampling time only, when shredding caddisflies arrived on the leaf bags. In the other perennial stream, leaf-mining chironomids entered fine-mesh bags and accelerated decomposition so that they lost more weight than the coarse-mesh bags. There was no difference in weight loss between fine and coarse-mesh leaf bags in the two intermittent streams. In 2018–19, decomposition was slower in dry reaches of intermittent streams than in perennial reaches. Leaf weight loss increased with the resumption of flow in intermittent streams, so that by the end of the experiment, similar amounts of leaf weight had been lost in intermittent and perennial reaches. Thus, although the temporal pattern of decomposition differed between intermittent and perennial reaches, after 320 days, they had reached a similar endpoint. Over similar experimental duration, mean leaf weight remaining in perennial reaches at the end of the experiment did not differ between the

Recent climate change is altering the timing, duration and volume of river and stream flows globally, and in many regions, perennially flowing rivers and streams are drying and switching to intermittent flows. Profound impacts on aquatic biota are becoming apparent, due in part to the strong influence of flow regime on the evolution of life history. We made predictions of life-history responses for 13 common aquatic invertebrate species (four caddisflies, five mayflies, two stoneflies, a dragonfly and an amphipod), to recent flow regime change in Australian mediterranean climate streams, based on historic studies in the same streams. Size distributions, phenology, voltinism and synchrony were compared, revealing five main responses. More than half of the species were restricted to perennially flowing streams and were absent from those that had switched to intermittent flows (including all four caddisfly species). These formerly common species are at risk of extinction as climate change progresses. Two mayfly species had divergent responses in voltinism and synchrony, and one relied on drought micro-refuges to persist. One stonefly species changed development timing to suit the new flow regime, and the amphipod species retreated to subterranean refuges. Two formerly common species were not detected at all during 2016–2017. In addition, a new mayfly species and a caddisfly species proliferated under new flow regimes, because they had life histories suited to brief hydroperiods. Importantly, previous life history rarely predicted species’ actual responses to climate-driven flow regime change, raising doubts about the veracity of predictions based on species traits. This is because a species’ potential for flexible phenology or growth rate is not necessarily indicated by life-history traits.

As climate change progresses, large (> 400 km2) fires are becoming more frequent across many biomes, often in association with intense drought. We analysed 5 years of stream macroinvertebrate data, collected before and after a wildfire that burnt > 750 km2 of the Grampians National Park, Australia. The wildfire occurred in 2006, during a 12-year drought (1997–2009). We tested the hypotheses that wildfire alters macroinvertebrate assemblage composition, and reduces taxon richness and among-stream variation. Five burnt and five unburnt headwater stream reaches were compared before and after the fire; a larger number of reaches were used to examine temporal trends in taxon richness. Wildfire altered macroinvertebrate assemblage composition and reduced among-stream variation in assemblages, but was not associated with low reach-scale taxon richness. Fire was associated with increased abundances of predators specialised for soft-sediments, and with reduced abundances of shredding and algal grazing caddisflies. In the short term, suspension feeder abundances increased, overwhelming the negative effects of drought on their abundance. Within 2 years post-fire, assemblages in burnt streams were similar to unburnt streams; within 3 years, among-reach variability in assemblage composition among burnt streams resembled that in unburnt streams. Invertebrate assemblages recovered rapidly in these streams despite the large areal extent of the fire. However, the frequency of wildfires is increasing, potentially permanently altering riparian vegetation structure and composition. As headwater streams depend on riparian vegetation for shading, woody debris and leaf litter, such permanent changes will likely affect biodiversity in headwater streams.

The Swan Coastal Plain was once covered by wetlands, but fewer than 30% of these natural wetlands remain. Many natural wetlands are seasonal — drying out in summer and autumn. Others are perennial, containing water year round.

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.

Climate change is modifying the timing of the onset of winter rainfall in southern Australia, at times creating brief inundation events in seasonal wetlands, termed 'false starts'. False starts may cause abortive hatchings of fauna emerging from sediment egg banks because wetlands dry out before invertebrates can complete their life cycle or reach a drying-resistant life stage. 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 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 5 days, then allowed to dry out for different time periods (10, 20 and 30 days) and then inundated for 5 days. Controls were inundated for time periods equivalent to the total duration of each false-start treatment (20, 30 and 40 days). 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 assembl

Intermittent stream systems create a mosaic of aquatic habitat that changes through time, potentially challenging freshwater invertebrate dispersal. Invertebrates inhabiting these mosaics may show stronger dispersal capacity than those in perennial stream systems. To relate different combinations of dispersal and drought survival strategies to species persistence, we compared the distribution and dispersal potential of six invertebrate species across all streams in a montane landscape where drying is becoming increasingly frequent and prolonged. Invertebrates were collected from seventeen streams in the Victoria Range, Grampians National Park, Victoria, Australia. The species analysed were as follows: the caddisflies Lectrides varians Moseley (Leptoceridae) and Agapetus sp. (Glossosomatidae); the mayflies Nousia AV1 and Koorrnonga AV3 (Leptophlebiidae); the water penny beetle Sclerocyphon sp. (Psephenidae); and a freshwater crayfish Geocharax sp. nov. 1 (Parastacidae). These species were widespread in the streams and varied in their dispersal and drought survival strategies. The distribution of each species across the Victoria Range, their drought responses and within-stream habitat associations were determined. Hypotheses of the dispersal capacity and population structure for each species were developed and compared to four models of gene flow: Death Valley Model (DVM), Stream Hierarchy Model (SHM), Headwater Model (HM) or panmixia (PAN). Molecular genetic methods were then used to infer population structure and dispersal capacity for each species. The large caddisfly Lectrides resisted drought through aestivation and was panmictic (PAN) indicating strong dispersal capacity. Conversely, the small caddisfly Agapetus relied on perennially flowing reaches and gene flow was limited to short distances among stream headwaters, resembling the HM. Both mayflies depended on perennial surface water during drying and showed evidence of gene flow among streams: Koorrnonga main

In many regions, climate change is prolonging dry periods in rivers and wetlands, exposing freshwater invertebrates to increased periods of desiccation. Invertebrates show a range of strategies for surviving desiccation, but the effects of the degree of exposure to desiccation on the expression of particular traits is unknown. This review synthesizes existing information on the desiccation responses of freshwater invertebrates to examine the flexibility of these survival strategies and the relationship between strategies and the degree of desiccation to which individuals are exposed. It focuses on desiccation at the small spatial scales experienced by individuals and clarifies the terminology of resting stages present during desiccation. We provide a key to terminology used for different forms of dormancy, so that appropriate terms may be used. All invertebrate groups showed a range of strategies for surviving desiccation. Sometimes, different traits were expressed among different populations of a species; however, it is unclear how many species show multiple desiccation response strategies. Many crustacean taxa showed physiological dormancy responses to desiccation that enabled survival for long periods (years). Insects often rely on emigration from drying waterbodies as flying adults or on larvae occupying damp refuges on the benthos. Altered water regimes may alter the phenology of desiccation responses, potentially increasing local extinctions, even in species capable of prolonged dormancy because of constraints on life cycles. However, there is limited empirical evidence demonstrating the flexibility of, or limitations to, expression of these survival strategies and their potential fitness costs.

Lectrides varians (Mosely) is a large, ecologically-important, caddisfly found in perennial and intermittent streams throughout much of eastern Australia. We conducted a population genetic analysis to investigate the dispersal potential of L. varians, building on previous works that have assessed life-history traits associated with drought resistance. Genetic analyses of L. varians from the Grampians region of Victoria, based on mitochondrial DNA sequence data, revealed extensive gene flow and a lack of genetic structure across the sample range (ΦST = 0.04). This suggests that the species is a strong disperser and is likely to be resilient to increased drying and habitat fragmentation under climate change considering other known resistance traits. However, during this study, two divergent genotypes were identified, indicating a potential species complex. A comprehensive phylogenetic analysis of L. varians across its current range was subsequently performed, confirming the species is indeed paraphyletic, consisting of one lineage that is restricted to the Grampians National Park and the other being widespread throughout south-eastern Australia. Further analyses revealed consistent morphological differences between these lineages supporting the notion that L. varians is a species complex. We discuss the implications of these findings with regard to conservation and taxonomy of this important invertebrate group.

Extreme events like wildfire, flooding and drought, and activities related to managing these events (fire dam, bridge and road construction and water regulation) potentially impact freshwater crayfish populations, although limited information exists. Our study analysed abundance data for four freshwater crayfish species across an 11-year period, including pre- and post-wildfire and post-flooding data, and described the impacts of human actions on their populations in the Grampians National Park in Victoria, Australia. Wildfire and flooding were generally associated with reduced crayfish abundances for Euastacus bispinosus, Cherax destructor, Geocharax falcata and Gramastacus insolitus, but in some habitats, C. destructor, G. falcata and G. insolitus did not decline. A general trend of decreasing abundances for all species was evident over the study period, likely due to the landscape-scale impacts of wildfire, flooding and the shrinking of available habitat during drought. Southeastern Australia is a crayfish biodiversity hot-spot and increased frequencies of wildfire, flooding and drought are forecast for this region as climate change progresses, threatening crayfish populations. Therefore, it is important that disaster recovery management seeks to minimise additional damage to crayfish habitat availability and connectivity.

Seasonally intermittent freshwater environments show large temporal changes in area and environmental conditions (which may be harsh). We investigated whether microhabitats that retain moisture could provide a refuge during drying in a seasonal wetland. 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. Ten microrefuges of each type were sampled for invertebrates, sediment and temperature during each of three hydrological phases: the damp phase (surface water absent 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. 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. 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 South Lake. Those species that depend on sediment fissures to survive may be threatened by the declining groundwater table in th

When intermittent streams flow, benthic algae develop from both colonising propagules and regrowing dried biofilm. We aimed to determine whether colonisation processes influence algal densities and taxonomic composition beyond the period immediately following commencement of winter flows, and whether regulation modifies those processes, in the Victoria Range, Australia. Stones were placed in two unregulated streams, and upstream and downstream of weirs in three regulated streams, after dry biofilm was removed. Epilithic algae on treatment and control stones were collected after winter flows (12 weeks). Treatment effects were still apparent in one (unregulated) stream, but not in the other streams. Algal assemblages and densities upstream and downstream of weirs differed, but there was no systematic pattern among streams. In intermittent headwater streams, recolonisation processes may influence algal assemblages until spring; but in most streams, the duration of influence will be shorter, depending on the assemblage composition in regrowth and refuges, which is also shaped by conditions during the previous flow season. If the effects of regulation depend on how idiosyncratic flow regimes and assemblage compositions influence recolonisation, they may be difficult to predict. Similarly, recovery trajectories for stream communities after drought will differ among streams, depending on whether biofilm can develop during potentially short seasonal flows.

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

Refuges protect plant and animal populations from disturbance. Knowledge of refuges from disturbance in mediterranean climate rivers (med-rivers) has increased the last decade. We review disturbance processes and their relationship to refuges in streams in mediterranean climate regions (med-regions). Med-river fauna show high endemicity and their populations are often exposed to disturbance; hence the critical importance of refuges during (both seasonal and supraseasonal) disturbances. Disturbance pressures are increasing in med-regions, in particular from climatic change, salinisation, sedimentation, water extraction, hydropower generation, supraseasonal drought, and wildfire. Med-rivers show annual cycles of constrained precipitation and predictable seasonal drying, causing the biota to depend on seasonal refuges, in particular, those that are spatially predictable. This creates a spatial and temporal mosaic of inundation that determines habitat extent and refuge function. Refuges of sufficient size and duration to maintain populations, such as perennially flowing reaches, sustain biodiversity and may harbour relict populations, particularly during increasing aridification, where little other suitable habitat remains in landscapes. Therefore, disturbances that threaten perennial flows potentially cascade disproportionately to reduce regional scale biodiversity in med-regions. Conservation approaches for med-river systems need to conserve both refuges and refuge connectivity, reduce the impact of anthropogenic disturbances and sustain predictable, seasonal flow patterns.

Intermittent streams drain over half the Australian mainland and provide water for humans and habitat for aquatic biota. Increased water extraction for human use together with climate change will likely reduce stream flow and extend dry periods across southern Australia, adversely affecting biota in both perennial and intermittent streams. Environmental flows may be released to protect stream ecosystems, however there is limited knowledge of biotic responses to flow releases in headwater streams. The aim of this study was to examine post-drying recovery of macroinvertebrate assemblages in regulated headwater streams following small environmental flow releases (0.4ML/day). To determine how flow releases affected macroinvertebrate assemblages, two streams that received environmental flows were compared with other regulated and unregulated streams that were either perennial or intermittent (some with perennial pools). The two streams that received environmental flows showed progressive increases in taxa richness downstream of the release point over time, and taxa richness also increased over a four week period. The downstream reach of one of the streams receiving environmental flows had an assemblage that resembled those of other perennial streams, while assemblages in the other stream were more similar to unregulated, intermittent streams. Relatively small environmental flow allocations can have positive impacts on invertebrate assemblages in small regulated streams over short time periods (1-4 weeks), indicating their potential benefit for ecological restoration of headwater streams.

Southern Australia is becoming warmer and drier as climate change progresses, creating serious threats to freshwater ecosystems that are dependent on the presence of water for their existence. The overall aim of this research project was to develop and evaluate four potential methods for enhancing the role, function and resilience of refuges for freshwater biodiversity in southern Australia. It focussed on means to maintain the physical conditions in refuges within ranges tolerable for species and to maintain connectivity that allows species to retreat to, and expand from, refuges. The four approaches studied were: • the feasibility of using cool-water releases (CWR) from reservoirs and shandying to control water temperature in rivers; • a method for deciding where streamside re-vegetation should occur in catchments to ensure maximum long-term negative effects on stream temperature; • the potential for artificial urban wetlands (i.e. anthropogenic habitat) to act as refuges for freshwater biodiversity against climate change; • a method for identifying redundant river regulation infrastructure and prioritizing artificial structures for removal during river restoration to improve connectivity along river channels for fauna movement. These four approaches were found to have the potential to address a range of objectives for refuge management, such as: reduce temperatures in refuges (1 & 2), increase number of refuges that act as colonization sources (all), assist dispersal into and out of refuges (all), increase biodiversity within refuges (all), increase permanence or resilience of refuges (all) and increase resistance or resilience of refuges during extreme events (1, 2 & 3). In particular, CWR could potentially be used to mimic natural thermal regimes, reduce the frequency and duration of extreme high temperature events and to assist movement of fish between thermal refuges, but further information and trials are required (1). Riparian planting can be used to reduce

Some freshwater species aestivate to resist drying; however, little is known about factors affecting post-aestivation survival. Climate change prolongs drying and may make short bursts of flow more frequent in southern Australian streams, thereby affecting aestivation success. The tolerance of larval Lectrides varians (Mosley) to drying was tested by inducing aestivation in dry or moist sediment and then re-immersing larvae and measuring survival and activity. Survival did not differ between individuals that were continually immersed (78%) or aestivating on moist sediment (70.5%) after 16 weeks. Survival was significantly lower on dry sediment (29.3%). Furthermore, some larvae showed delayed responses to re-immersion; 65% of individuals showed activity within 4.5h, whereas over 30% of larvae did not become active until 72h after re-immersion. L. varians can survive extended periods (112 days) without surface water, showing a bimodal response to re-immersion that increases the likelihood of population persistence by enabling some larvae to remain aestivating during short-lived bursts of stream flow. L. varians populations will therefore be more robust to prolonged stream drying and short-lived flow events than are some other insect taxa, although as the duration of aestivation increases larval survivorship decreases, suggesting that there are limits to the flexibility of aestivation traits.

Summary 1. If resistance traits drive recolonisation after drought, then drought refuges should contribute strongly to assemblage composition within streams. If resilience traits drive recolonisation, macroinvertebrates emerging from refuges may disperse widely, colonising many streams. To determine whether the contribution of drought refuges to macroinvertebrate recolonisation in non-perennial streams was mostly local (within stream) or broader scale (across streams), we measured the association between the composition of invertebrate assemblages in different types of in-stream drought refuge and the assemblage composition of streams when flow resumed. 2. We sampled 16 streams of varying hydrological regime on the western side of the Victoria Range in the Grampians National Park, Victoria, Australia. Drought refuges (perennial pools, dry sediment, damp sediment, seeps, patches of leaf litter, beneath stones) were identified and sampled during autumn. Most taxa were found in perennial pools; few taxa were found aestivating beneath stones or having desiccation-resistant stages in dry sediment. Perennial pools and perennially flowing reaches were the refuges that harboured the greatest diversity of macroinvertebrate taxa. 3. Streams were sampled again during spring. Assemblage composition of non-perennial reaches in spring was unrelated to composition in nearby refuges in the previous autumn. In contrast, assemblage composition in perennial reaches during spring was strongly correlated with composition during autumn. Therefore, drought refuges did not directly influence assemblage composition locally within non-perennial streams. Rather, both perennially flowing reaches and perennial pools acted as drought refuges across the broader landscape. Resilience traits are likely to drive recolonisation in these streams. 4. Monitoring of drought refuges in a particular stream will therefore not predict species composition when flow resumes. Drought refuges are likely to susta

In some arid, semi-arid or Mediterranean climate regions, increased water extraction combined with climate change will prolong periods of drought in non-perennial streams, but the effects on macroinvertebrate populations are poorly understood. Drought refuges allow species to survive drying but their use depends on species' traits, and refuge availability depends on landscape structure. This review evaluates the utility of existing ecological concepts for predicting the role of drought refuges for sustaining biodiversity in non-perennial streams. We also suggest traits that may determine invertebrate species' resistance or resilience to prolonged drying. Parts of the likely responses by populations to increased stream drying are described by existing ecological concepts, such as the biological traits of species and their interaction with the habitat templet, barriers to dispersal and metapopulation dynamics, the use of drought refuges, habitat fragmentation and population and landscape genetics. However, the limited knowledge of invertebrate life histories in non-perennial streams restricts our ability to use these concepts in a predictive manner. In particular, reach or pool occupancy by species cannot be accurately predicted, but such predictions are necessary for evaluating potential management actions such as the use of environmental flows to sustain drought refuges during dry periods.

Restoration is increasingly the focus of ecosystem management. Few conceptual models exist for predicting the consequences of restoration, especially those that predict the stages of recovery following restoration. Existing models focus either on defining endpoints for recovery or on defining ecosystem processes, but often do not identify barriers to recovery or potential negative effects of restoration. We describe a conceptual model that identifies the outcomes of the recovery pathways following flow restoration in rivers: the Recovery Cascade Model. The model identifies six general aspects of recovery following restoration: physical ecosystem change; creation of, or improvement in habitat condition; reconnection of the restored area to adjacent ecosystems; recolonization of the restored area; resumption of ecological processes; re-establishment of biotic interactions and reproduction by colonists in the restored area. These aspects may occur in sequence, such that recovery is blocked by a single barrier. The model accommodates feedback loops and includes strong connections between physical processes and ecosystem processes, but also identifies factors that are important in achieving endpoints such as potential barriers to further recovery. Identification of barriers to recovery enables improved planning to maximise the positive effects of restoration. By focussing on outcomes, the model provides a planning tool for managers that can be adapted for different ecosystems and restoration methods and which can be used to identify the amenities that an ecosystem will deliver at different stages of recovery. Ecosystem recovery is as much about overcoming barriers as it is about restorative actions.

1. Flow conditions were modified over patches of river bed in three rivers in southwestern Australia to determine the effects of turbulence on benthic invertebrate communities. 2. Artificial structures to increase downstream turbulence were developed in a laboratory flume. In the field, these increased turbulence intensity by 35% for a 20% reduction in velocity. 3. Patches of gravel were placed in each river and turbulence-generating structures allocated randomly to half of these, creating treatment patches. An acoustic Doppler velocimeter was used to measure flow conditions over both treatment and control patches at several heights above the bed. After 6 weeks, the invertebrate fauna of the gravel patches were sampled to examine the response to modified flow conditions. 4. The treatments increased relative turbulence intensity twofold for a reduction in velocity of between 3 and 5 cm s-1, but turbulence intensity was significantly higher in only one of the three rivers. 5. There were no significant effects of increased relative turbulence intensity on any aspect of the invertebrate assemblage. This may be a result of the fairly small increase in relative turbulence intensity created during the experiment, the spatial scale of the manipulation or the types of stream community studied.