Paul Close

Upper thermal tolerances of key taxonomic groups of stream invertebrates

Southwestern Australia has already undergone significant climatic warming and drying and water temperatures are increasing particularly in small streams where riparian vegetation has been cleared. The ability to predict how freshwater fauna may respond to these changes requires understanding of their thermal tolerances. A review of relevant literature and laboratory testing of four aquatic species from southwestern Australia were used to compare upper thermal tolerance (UTT) among key taxonomic groups. UTT for selected species determined by LT50 tests were similar to that of species tested elsewhere. Mean UTT, based on relevant literature and LT50 experiments, ranged from 22.3°C for Ephemeroptera to 43.4°C for Coleoptera. Mean UTT for both Coleoptera and Odonata (41.9°C) were significantly higher than those for all the other groups (22.3–31.5°C) with the exception of Planaria. The mean UTT value of 22.3°C for Ephemeroptera was significantly lower than for Decapoda (29.6°C), Trichoptera (30.1°C) and Mollusca (31.5°C). For three insect orders tested, eurytherms had significantly higher UTT values than stenotherms. The variation in UTT among taxa suggests that additional thermal shifts, caused by riparian disturbance and/or climate change, are likely to create novel assemblages due to the replacement of temperature-sensitive taxa by more tolerant taxa. This has implications for the sustainability of regionally important endemic cool water species.

First record of 'climbing' and 'jumping' by juvenile Galaxias truttaceus Valenciennes, 1846 (Galaxiidae) from south-western Australia

Abstract. Upstream migration of juvenile stages of temperate Australian amphidromous fish typically coincides with seasonally low river discharge when hydraulic (e.g. cascades) and physical (e.g. rock bars) barriers may be common. The ability to ‘climb’ or ‘jump’ may be expected to assist in negotiating low-flow barriers; however, it is presumed to be limited to a few native Australian freshwater fishes. Juvenile stages of Galaxias truttaceus Valenciennes, 1846 were observed ‘climbing’ and ‘jumping’ to successfully negotiate a low, vertical weir wall during their upstream recruitment migrations in south-western Australia. Based on this observation, we propose initial definitions for ‘climbing’ and ‘jumping’ to describe locomotory strategies employed by fishes to negotiate obstacles that would otherwise prevent free passage by normal swimming behaviour. Greater knowledge of the climbing, jumping and swimming performance, especially for small-bodied species and early life stages, will help improve the management of instream barriers for this critically endangered species and other freshwater fishes of southern Australia.

Macroinvertebrates in the bed sediment of the Yellow River

Extensive agricultural, industrial and urban development in the Yellow River, China, have modified the sediment-water balance, flow and inundation regimes, longitudinal connectivity, integrity of riparian vegetation, and water quality. Macroinvertebrate assemblages in the bed sediment of main channel and major reservoirs of the Yellow River are described in detail for the first time. A total of 74 taxa comprising 17 taxa of oligochaetes, 48 taxa of aquatic insects, 5 taxa of molluscs, and 4 taxa of other animals were recorded. A range of feeding guilds were represented, including, collector-gatherers (32 taxa), predators (17 taxa), scrapers (16 taxa), shredders (6 taxa) and collector-filterers (2 taxa). Both the mean density and biomass of macroinvertebrates were significantly higher in sites located in the artificial reservoirs compared with the main river channel. Assemblages varied spatially; Oligochaetes dominated assemblages in upper reaches, insects dominated in middle reaches and other animals (e. g. Crustacea) dominated in lower reaches. Collector-gatherers were dominant throughout the entire river. Classification analysis identified five site-groups on the basis of macroinvertebrate presence/absence: downstream of reservoirs; vegetated sites; reservoir sites; polluted sites, and; lower-reach sites. Lower macroinvertebrate richness, density and biomass, compared with other similar large rivers, were attributed to modification of the sediment-water balance and associated disturbance of benthic habitats. Pollution, stability of sediment and sediment concentration combined to influence the distribution of macroinvertebrates. This knowledge will substantially benefit the recent focus on the health and environmental water requirements of the Yellow River.

Customary and recreational fishing pressure: large-bodied fish assemblages in a tropical, intermittent Australian river

Permanent waterholes in intermittent rivers of northern Australia support a diverse piscifauna and are popular areas for customary and recreational fishing. The present preliminary study explored the perception that fishing reduces the abundance of targeted, large-bodied species that become restricted to disconnected waterholes during the distinct dry season. River sites in the Fitzroy River catchment, Western Australia, could be clearly classified as experiencing either high or low fishing pressure by using metrics of human ‘accessibility’. The abundance of Hephaestus jenkinsi and Lates calcarifer, targeted by both recreational and customary fishers was highly correlated with accessibility and showed a negative relationship with fishing pressure. Non-target species showed no discernible trend. We estimated that 38% of river length remains subject to relatively low fishing pressure. These preliminary relationships suggest that fish harvest can potentially alter the structure of fish assemblages in disconnected habitats. The potential impact of fishing on the sustainability of fish populations is, most likely, greatest for non-diadromous species and will become more apparent with increasing distance from recolonisation sources. Combining management techniques that maintain recolonisation and recruitment potential with traditional fisheries management strategies (e.g. bag and size limits) presents a suitable approach to mitigate the effects of fish harvesting from tropical intermittent rivers.

Collaborative research partnerships inform monitoring and management of aquatic ecosystems by Indigenous rangers

Aquatic ecosystems are critical to the long-term viability and vibrancy of communities and economies across northern Australia. In a region that supports significant cultural and ecological water values, partnerships between Indigenous and non-Indigenous stakeholders can benefit aquatic ecosystem management. We present, as a case study from the Kimberley region of Western Australia, a collaborative research program that successfully documented Indigenous and Western Scientific knowledge of remote wetlands, using a variety of field-based activities, questionnaires, interviews and workshops. The sharing of knowledge between Indigenous and non-Indigenous research partners facilitated a comprehensive understanding of ecosystem values, threats, processes, management priorities and aspirations. These formed the basis of a management plan and monitoring tools, designed to build the capacity of an Indigenous ranger group to engage in research, monitoring and management of wetlands. The project provides a useful example of the benefits of collaborations in the context of remote-area management where local communities are responsible for environmental management and monitoring, such as is the case in northern Australia and presumably other areas of the world.

Resolving the taxonomy, range and ecology of biogeographically isolated and critically endangered populations of an Australian freshwater galaxiid, Galaxias truttaceus

The spotted galaxias (or trout minnow), Galaxias truttaceus, is a species that is restricted to south-western and south-eastern Australia, but there has long been conjecture as to whether the geographically and Critically Endangered Western Australian populations represent a subspecies (Galaxias truttaceus hesperius). We provide evidence that Western Australian populations, on the basis of a combination of genetic, geographic and ecological criteria, should be considered an evolutionary significant unit, which merits management as a high conservation priority. Substructure at nuclear and matrilineal genetic markers is not suggestive of species-level divergence, but rather of discrete western and eastern Australian subpopulations with limited contemporary gene flow. In contrast to many eastern populations that are diadromous, all western populations are potamodromous. Adults live and spawn in riverine habitats and larvae drift downstream to coastal lakes, where they spend several months, before undertaking a distinct upstream recruitment migration as juveniles to colonise riverine habitats. Instream barriers that disconnect riverine and lentic habitats restrict distributional range and presumably affect reproductive success of Western Australian populations. Conserving the remaining populations in Western Australia will require ongoing efforts to reduce the impact of emerging threats, particularly those related to instream barriers, introduced species and reductions in water quantity and quality.

Hierarchical multi‐taxa models inform riparian vs. hydrologic restoration of urban streams in a permeable landscape

The degradation of streams caused by urbanization tends to follow predictable patterns; however, there is a growing appreciation for heterogeneity in stream response to urbanization due to the local geoclimatic context. Furthermore, there is building evidence that streams in mildly sloped, permeable landscapes respond uncharacteristically to urban stress calling for a more nuanced approach to restoration. We evaluated the relative influence of local-scale riparian characteristics and catchment-scale imperviousness on the macroinvertebrate assemblages of streams in the flat, permeable urban landscape of Perth, Western Australia. Using a hierarchical multi-taxa model, we predicted the outcomes of stylized stream restoration strategies to increase the riparian integrity at the local scale or decrease the influences of imperviousness at the catchment scale. In the urban streams of Perth, we show that local-scale riparian restoration can influence the structure of macroinvertebrate assemblages to a greater degree than managing the influences of catchment-scale imperviousness. We also observed an interaction between the effect of riparian integrity and imperviousness such that the effect of increased riparian integrity was enhanced at lower levels of catchment imperviousness. This study represents one of few conducted in flat, permeable landscapes and the first aimed at informing urban stream restoration in Perth, adding to the growing appreciation for heterogeneity of the Urban Stream Syndrome and its importance for urban stream restoration.

Incorporating climate change into recovery planning for threatened vertebrate species in southwestern Australia

Recovery plans are the main tool used for restoration of threatened species in Australia, and identification of key threatening processes is an important feature of them. The aim of this study was to identify how climate change can be incorporated into the recovery planning process using a case study of threatened vertebrates in a global biodiversity hotspot, southwestern Australia. Analysis of 79 recovery planning documents for threatened vertebrate species in the region found that prior to the year 2004, climate change was not included as a threatening process. Post 2004, 32 of 54 (59.3%) documents included climate change as a threatening process. Using bioclimatic modelling, 43 of these species were ranked in terms of their potential exposure to climate change, and a gradient of management intervention aimed at mitigating their exposure to climate change was proposed. This intervention gradient ranged from active management actions aimed at species potentially at risk of extinction due to climate change, through to preservation of habitat in species predicted to lose between 0 and 25% of their current population size. It was proposed that as a priority, the recovery documentation of the 20 species predicted to be most at risk and thus needing a high level of management intervention should identify climate change as a key threatening process, and that more comprehensive analyses of climate change vulnerability be undertaken for these species. Such an approach aimed at prioritising climate change mitigation in threatened species would be useful for other regions where it has been predicted that climate change could have a negative impact on biodiversity.

Recruitment and growth of two small-bodied resident fish species (Gobiidae and Atherinidae) in oligohaline, seasonally open lagoons

Spatio-temporal recruitment patterns, growth and survival of the Swan River goby Pseudogobius olorum and western hardyhead Leptatherina wallacei are described from two small, coastal lagoons on the south coast of Western Australia. In these lagoons, estuarine salinity dynamics were relatively stable over much of the autumn-spring period when freshwater inputs from rivers were reduced and there was no oceanic connection. Preflexion and flexion stages of both fish species contributed strongly to population size structure in downstream reaches, whereas upstream reaches were dominated by postflexion larvae and juvenile stages. Spawning of both species was protracted and largely asynchronous, although the episodic presence of stronger preflexion and flexion cohorts suggested some synchronized spawning had occurred. Comparison with estuarine conditions over this period provided evidence that synchronized spawning may be related to temperature and salinity variations from a combination of freshwater inputs and periods of marine exchange. Uninterrupted growth and the progression of cohorts through to juvenile stages were consistent with the generally stable estuarine conditions. Larval and juvenile stages of both species were also tolerant of abrupt changes in salinity and temperature, which occurred due to a non-seasonal oceanic connection. These findings were consistent with the euryhaline nature of adults of both species.

Macroinvertebrate and covariate data

Tab-1: Macroinvertebrate catch data at sample sites. Tab-2: Covariate data at sample sites.