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Salinity is increasing in many naturally fresh waters because of human activities, and there are concerns about the ecological effects of these increases. Salinity, as with any stressor, can affect organisms both directly and indirectly. In a previous study (Bray et al. 2019), we evaluated the relative importance of direct and indirect effects of increased salinity on stream invertebrates. Chessman (2021) criticised that study, claiming that the biotic treatments were confounded and did not directly test the hypotheses. Chessman (2021) also conducted a reanalysis of the data. We show through the analysis of new data that our biotic treatments were not confounded and that the conclusions made by Chessman (2021) were probably a consequence of the low statistical power of his analysis. Consequently, we argue that Chessman’s (2021) comments do not substantively alter the conclusions of our study, and we provide more evidence to support the conclusions of our previous publication. The study of biota–stressor interactions is increasingly relevant to a wide range of global ecosystems. There is a need to develop tractable experimental and survey designs that address these problems, and we identify further avenues for study of these complex issues.

Declining water quality and ecological condition is a typical trend for rivers and streams worldwide as human demands for water resources increase. Managing these natural resources sustainably is a key responsibility of governments. Effective water management policies require information derived from long-term monitoring and evaluation. Biological monitoring and assessment are critical for management because bioassessment integrates the biological, physical and chemical features of a waterbody. Investment in nationally coordinated riverine bioassessment in Australia has almost ceased and the foci of management questions are on more localised assessments. However, rivers often span political and administrative boundaries, and their condition may be best protected and managed under national policies, supported by a coordinated national bioassessment framework. We argue that a nationally coordinated program for the bioassessment of riverine health is an essential element of sustainable management of a nation’s water resources. We outline new techniques and research needed to streamline current arrangements to meet present-day and emerging challenges for coordinating and integrating local, regional and national bioassessment activities. This paper draws on international experience in riverine bioassessment to identify attributes of successful broad-scale bioassessment programs and strategies needed to modernise freshwater bioassessment in Australia and re-establish national broad-scale focus.

The unique Australian monotreme, the platypus (Ornithorhynchus anatinus) potentially exerts a strong top-down influence on riverine food webs in eastern Australia. However, despite considerable interest in the evolutionary history and physiology of the platypus, little is known of its trophic relationships. To address this lack of knowledge we used stable isotope analysis, in combination with the analysis of food items stored in cheek pouches, to determine its position in a typical riverine food web. This was the essential first step in the process of designing a larger study to investigate the relative importance of top-down and bottom-up effects in rivers where the platypus occurs. We found that platypuses were feeding on a wide range of benthic invertebrates, particularly insect larvae. The similarity of δ13C and δ15N values recorded for the platypus, a native fish (Galaxias sp.) and the exotic mosquitofish (Gambusia holbrooki) indicated dietary overlap and potential competition for the same resources. Although cheek pouch studies identify most of the major groups of prey organisms, the potential for contribution of the soft-bodied organisms such as larval dipterans, is suggested by stable isotope analysis, indicating that the use of both techniques will be important in future ecological investigations.

Clearing native vegetation has pervasive effects on stream and river ecosystems worldwide. The stated aims of replanting riparian vegetation often are to restore water quality and to re-establish biotic assemblages. However reach-scale restoration may do little to combat catchment-scale degradation, potentially inhibiting restoration success. Whether reinstating biodiversity is a realistic goal or appropriate indicator of restoration success over intermediate timeframes (

Anthropogenic impacts on stream ecosystems generate changes in nutrient and carbon availability which act as stoichiometric challenges to consumers. We tested the hypothesis that removal of Eucalyptus riparian vegetation alters in-stream resource stoichiometry with flow-on effects for a benthic consumer (the freshwater crayfish, Cherax destructor). Sites with high and low riparian canopy cover were selected on a lowland stream in south-eastern Australia. A reduction in riparian vegetation canopy cover was associated with decreased terrestrial detritus (low nutritional quality; high carbon to nitrogen (C : N) ratio) and increased cover of macrophytes and filamentous algae (high quality; low C : N ratio). This resource-quality shift was associated with a small but significant decrease in C. destructor C : N ratio (molar ratio of muscle tissue). This suggests that the animals are deviating from homeostasis and may be in better condition in the stream pools dominated by in-stream productivity. A significant negative relationship between C. destructor length and C : N ratio was observed, suggesting that resource-quality impacts may differ with age. The present study has shown that riparian loss alters stoichiometric interactions in stream benthic ecosystems, with potential consequences for stream processes such as nutrient cycling. Ecological stoichiometric theory should therefore be further utilised to make predictions of ecological impacts in freshwater systems.

Studies of the effects of biodiversity on ecosystem function (BDEF) have largely found positive, saturating relationships. However, these studies have been criticised for generating species loss randomly when real extinctions are strongly biased toward rare species. We investigated BDEF relationships in the mollusc fauna of an intertidal rock platform at Griffiths Point, San Remo, south-east Victoria, Australia. Field surveys found that areas with the lowest function (mollusc biomass) were associated with lowest diversity. Excluding individual species from experimental enclosures affected function differentially depending on species’ initial abundance. Rectangular enclosures were attached to the rock platform enabling molluscs to be enclosed while allowing sea water to flow through. Removal of the most abundant species had a positive effect on mollusc biomass, suggesting an inhibition of the other species in the community. In the absence of the most common species, the less abundant species were more productive in combination than when present singly. Taken collectively, these results provide evidence for a relationship between biodiversity and ecosystem function which is a product of both diversity per se and species identity.

Freshwater ecosystems are a foundation of our social, cultural, spiritual and economic well being. The degraded condition of many of Australia’s river ecosystems is testament to our failure to manage these resources wisely. Ecosystem science involves the holistic study of complex biophysical systems to understand the drivers that influence ecological pattern and process. Ecosystem science should underpin both water management and policy. Our understanding of aquatic ecosystems lags behind the increasing problems caused by past land and water management. Current post-graduate training programmes will not provide the aquatic ecosystem scientists needed by government and management agencies to prevent further degradation. We advocate new initiatives to capture the skills, knowledge and innovation of our research community by engaging scientists and managers in large-scale, long-term ecosystem science programmes across Australia and to integrate these programmes with community aspirations, policy, planning and management. We call on management agencies to increase their support for and uptake and use of ecosystem science. We also advocate establishment of national archives for long-term ecologically-relevant data and samples, and clear custodial arrangements to protect, update and facilitate knowledge-transfer. These initiatives need to be supported by more extensive, better-funded post-graduate and post-doctoral programmes in ecosystem science and management.