Paul Reich

Using species distribution models to infer potential climate change-induced range shifts of freshwater fish in south-eastern Australia

There are few quantitative predictions for the impacts of climate change on freshwater fish in Australia. We developed species distribution models (SDMs) linking historical fish distributions for 43 species from Victorian streams to a suite of hydro-climatic and catchment predictors, and applied these models to explore predicted range shifts under future climate-change scenarios. Here, we present summary results for the 43 species, together with a more detailed analysis for a subset of species with distinct distributions in relation to temperature and hydrology. Range shifts increased from the lower to upper climate-change scenarios, with most species predicted to undergo some degree of range shift. Changes in total occupancy ranged from –38% to +63% under the lower climate-change scenario to –47% to +182% under the upper climate-change scenario. We do, however, caution that range expansions are more putative than range contractions, because the effects of barriers, limited dispersal and potential life-history factors are likely to exclude some areas from being colonised. As well as potentially informing more mechanistic modelling approaches, quantitative predictions such as these should be seen as representing hypotheses to be tested and discussed, and should be valuable for informing long-term strategies to protect aquatic biota.

Using biological information to support proactive strategies for managing freshwater fish during drought

This paper provides an assessment of the biological attributes of fish species in south-eastern Australia and rates their potential risk from the impacts of drought. We used scientific literature and expert opinion to conduct a semiquantitative assessment of attributes considered to influence species resistance and resilience to drought for 15 freshwater fish species found in south-eastern Australia. We also present a conceptual framework to guide management of fish populations during drought. The framework focuses on (1) quantifying spatial variation in the severity of drought impacts on particular habitats (rivers, wetlands etc.), (2) assembling information on drought sensitivities of regionally important species, (3) identifying high risk areas (based on species sensitivity and drought severity), (4) determining and implementing appropriate management actions (pre-emptive, responsive), (5) monitoring outcomes and (6) disseminating information on outcomes. In many regions, historic population declines will serve to exacerbate the impacts of drought, and thus are a major threat to successful recovery from drought. Although we discuss both long-term, pre-emptive planning and short-term, responsive management actions, we contend that a long-term view is required to successfully address the threats posed by drought. Furthermore, although droughts clearly represent a severe disturbance to fish populations, ultimately it is anthropogenic factors that exacerbate drought and constrain recovery pathways (at global, regional and local scales), rather than drought per se. These factors must be addressed if we are to ensure the long-term viability of fish populations in inland aquatic ecosystems.

Ecological risks and opportunities from engineered artificial flooding as a means of achieving environmental flow objectives

Restoration of floodplain ecosystems through the reinstatement of floods is often hampered by insufficient water as a result of competing human demands. An emerging alternative approach relies on floodplain infrastructure – such as levees, weirs, regulators, and pumps – to control water levels within floodplains without requiring landscape-scale overbank floods. This technique, albeit water efficient and capable of achieving some ecological targets, does not mimic the hydraulics, hydrodynamics, and lateral connectivity of natural floods. Engineering approaches like this may risk detrimental ecological outcomes, including reductions in biotic connectivity, river–floodplain productivity, and water quality, and thus may fail to support the range of ecological processes required to sustain healthy river–floodplain systems. Here, we review the potential benefits, risks, and mitigation options associated with engineered artificial flooding. Given the growing challenge of equitable water allocation, further research on and monitoring of engineered floods as a tool to sustain floodplain ecosystems are urgently required.

Association of reduced riparian vegetation cover in agricultural landscapes with coarse detritus dynamics in lowland streams

Studies were conducted on streams flowing through agricultural floodplains in south-eastern Australia to quantify whether reductions in riparian canopy cover were associated with alterations to the input and benthic standing stocks of coarse allochthonous detritus. Comparisons were made among three farmland reaches and three reaches within reserves with intact cover of remnant overstorey trees. Detritus inputs to these reaches were measured monthly over 2 years using litter traps. Direct inputs to streams within the reserves were relatively high (550–617 g ash free dry weight (AFDW) m–2 year–1), but were lower at farmland reaches with the lowest canopy covers (83–117 gAFDW m–2 year–1). Only a minor fraction of the total allochthonous input (<10%) entered any of the study reaches laterally. The mean amounts of benthic detritus were lowest in the most open farmland reaches. Standing stocks of benthic detritus were found to be highly patchy across a large number of agricultural streams, but were consistently very low where the streamside canopy cover was below ~35%. Canopy cover should be restored along cleared agricultural streams because allochthonous detritus is a major source of food and habitat for aquatic ecosystems. Given the absence of pristine lowland streams in south-eastern Australia, those reaches with the most intact remnant overstorey canopies should be used to guide restoration.

Bird assemblages of a fragmented agricultural landscape and the relative importance of vegetation structure and landscape pattern

Many of the world’s agricultural areas have greatly reduced levels of natural vegetation. This results in highly fragmented mosaic landscapes with multiple land-use types. We examined the importance of vegetation and landscape pattern by comparing the bird assemblages of riparian zones, non-riparian forest patches, and pasture in a fragmented agricultural landscape in south-eastern Australia. Bird surveys were conducted every four weeks at 27 sites in the Goldfields region of central Victoria for one year. The landscape context (position and shape of patches) and vegetation attributes were measured for each site. We found that bird assemblages strongly differed among these landscape elements. Mean abundance was significantly greater at forested patches, and there was a three-fold reduction in species richness at pasture sites. Bird assemblage structure was influenced substantially more by vegetation than by the landscape context of sites. Our results indicate that riparian vegetation is a key element for avian diversity, even in massively altered landscapes. The restoration of riparian vegetation and its connectivity with adjacent forest types would greatly benefit bird assemblages in agricultural areas.

Floods Down Rivers: From Damaging to Replenishing Forces

Publisher Summary This chapter draws attention to the similarities and differences in the physical characteristics of floods and their ecological effects in upland and lowland ecosystems. It describes the physical nature of floods in upland and lowland systems and examines the ecological response and importance of floods in each of these settings. High water events, floods, as disturbances are a major force shaping the ecology of streams and rivers. In constrained streams, usually in upland areas near the source, floods are marked by their high power—high velocities and shear stress. Such floods can change the shape of the channel, moving and scouring sediments, degrading and creating habitat, and removing and damaging biota. Covering recent developments in the ecological understanding of floods, the chapter highlights the damaging and replenishing nature of floods in different ecosystems. The chapter also emphasizes on examples drawn from the Murray–Darling Basin, a system that harbors a wide variety of watercourses and has been a major focus for aquatic ecosystem research in Australia.

Patterns of composition and abundance in macroinvertebrate egg masses from temperate Australian streams

Quantitative samples of lotic invertebrate egg masses were collected on two occasions from three riffles along two rivers within the Acheron River catchment, south-eastern Australia. Sampling was stratified to compare the abundance and composition of egg masses on submerged rocks with rocks that protruded above the water surface within each of three substrate size classes. The egg mass fauna of both rivers was found to be both species rich and abundant. Egg masses belonging to Diptera and Trichoptera represented the majority of material collected, with approximately 70% of all taxa common to both rivers. In particular, egg masses of Chironomidae, Hydrobiosidae, Hydroptilidae and Hydropsychidae dominated most samples numerically. Descriptions of the egg masses belonging to 17 taxa are provided, as well as preliminary estimates of hatching times and observations of egg-laying and post-hatching behaviour for some species. Large rocks (> 30 cm maximum diameter) that protruded above the water surface consistently yielded the highest number of egg masses for all common taxa. For common taxa, between 74% and 100% of all egg masses were found on large emergent rocks. Of the common taxa, little variation in egg mass abundance was detected between sampling times or between sites within each river. Exceptions were hydroptilids and chironomids, which were completely absent from some time/site combinations, suggesting a degree of synchrony in egg-laying behaviour. For all common taxa, the greatest source of variation in egg mass numbers appeared at the level of individual rocks, where a high degree of spatial aggregation was apparent (as described by Lloyds index of patchiness).

Loss of riparian vegetation alters the ecosystem role of a freshwater crayfish (Cherax destructor) in an Australian intermittent lowland stream.

Abstract Loss of riparian vegetation surrounding streams can affect instream biota by altering stream characteristics, such as terrestrially derived detrital inputs and instream productivity. Omnivorous crayfish can be a dominant component of stream biota and are considered a keystone species because of their ability to forage at multiple trophic levels. Resource shifts caused by changes in riparian canopy have the potential to influence crayfish diet and growth. We investigated the effects of changes in canopy cover on the crayfish Cherax destructor in a southeastern Australian lowland stream. We compared the diet of C. destructor between sites with and without riparian cover and determined how differences in the quantity of food resources between sites affected crayfish growth. The availability of basal (plant, algae, and detrital) resources was related to the presence of a riparian canopy. Aquatic macrophytes were more common at sites with no canopy cover and terrestrially derived leaf litter was more abundant at sites with an intact canopy. Stable isotope and gut content analyses of crayfish diet indicated a shift toward autochthonous food sources in individuals from sites with no canopy cover. In laboratory feeding trials, crayfish had higher growth rates when fed macrophyte material than when fed terrestrially derived leaf litter. Insights gained into resource use by crayfish, particularly the importance of aquatic invertebrates in crayfish diet, emphasize the merits of conducting both gut content and stable isotope analyses to assess short- and longer-term aspects of diet. Further structural and functional impacts of changes to riparian condition should be investigated, but the trophic role of C. destructor in stream food webs appears to be sensitive to alterations in the dominant basal resources associated with changes in riparian canopy.

Provision of environmental flows promotes spawning of a nationally threatened diadromous fish

Detailed understanding of flow-ecology requirements for aquatic biota underpins the use of environmental flows as an effective restoration tool in regulated rivers. However, flow recommendations are often overly simplistic and insufficient to provide the necessary environmental requirements for these biota. This is often due to failure to gain and integrate information on individual species ecology and, by using coarse generalisations, about flow-ecology responses. To inform more effective delivery of environmental flows, we investigated spawning responses of the threatened Australian grayling (Prototroctes maraena) to environmental flows over 2 years in three coastal rivers. Spawning activity was highest during within-channel flow pulses, especially during periods of environmental flow delivery. Peak spawning occurred in late autumn and was positively related to flow duration. This result has important implications for environmental flows management in regions where water is scarce and there is potential conflict among multiple users because, for Australian grayling, it is not necessarily the volume of water released that is important, but how the flow is delivered. Our study demonstrated the importance of quantifying flow-ecology relationships via targeted monitoring and research so as to develop appropriate flow regimes, and should encourage managers to examine more critically the logic behind generalised environmental flow objectives.

Stream macroinvertebrate community responses to fire: are they the same in different fire-prone biogeographic regions?

Droughts, fires, and floods are natural disturbances influencing aquatic ecosystems. If drought is accompanied by fires, and if fires are closely followed by floods, teasing apart their distinctive and potentially interactive responses can be difficult. We compared the responses of macroinvertebrate communities to fire via comparisons of streams in burned and unburned catchments in 3 fire-prone biomes that differ biogeographically and climatically (northwestern Mediterranean, southeastern Australia, and northwestern intermountain USA). The responses of macroinvertebrate communities in streams in burned catchments were similar in all biogeographic regions, but the magnitude of these responses varied. Fire combined with high seasonal stream flows, flooding, or drought was associated with reduced measures of taxonomic richness and increased abundance, especially of r-strategist taxa. Differences between sites in burned and unburned catchments were consistently stronger in southeastern Australia than in northwestern intermountain USA and northwestern Mediterranean regions. Our observations suggest that the timing and magnitude of postfire flows (snowmelt, seasonal high flows) may substantially alter the recolonization process and override fire effects, and that drought may play a strong role in limiting the resilience and resistance of macroinvertebrate communities in streams in catchments that have experienced wildfire.