Explore the vast range of titles available.

Northern Australia is considered a ‘lifeboat’ region for globally threatened shark and ray species (elasmobranchs), although much of the region is understudied. The Roper River in the Northern Territory’s Gulf of Carpentaria has been inadequately surveyed, with most elasmobranch data gained opportunistically through freshwater fish surveys. This study aimed to report the occurrence of elasmobranch species in the Roper River through targeted field surveys conducted between 2016 and 2024 and to review data from other sources. Four euryhaline species were recorded, comprising two sharks, a sawfish, and a stingray. Records of the globally Vulnerable speartooth shark (Glyphis glyphis) represented a significant range extension and the documentation of a new reproductive population. Records of the Critically Endangered largetooth sawfish (Pristis pristis) extended almost 400 km upstream, highlighting extensive use of the river system. A predominantly marine species, the Critically Endangered giant guitarfish (Glaucostegus typus) was observed in brackish estuarine waters, approximately 15 km upstream from the river mouth. Further research is required to develop a more thorough understanding of abundance, life history, and population connectivity for these species in this river system. Given the documentation of threatened species, the potential impacts of fisheries, water allocations, and climate change require assessment.

Natural mortality can be used as a measure of a species’ resilience and is widely used in the management of fish species. Natural mortality can be calculated using life history parameters, although this is often not possible for data-poor species. Acoustic telemetry provides an accurate alternative to estimate natural mortality based on relocations over time. Northern Australia’s river sharks, the Northern River Shark ( Glyphis garricki ) and Speartooth Shark ( G. glyphis ), are two rare and threatened species occurring in rivers, estuaries, and inshore marine waters. This study aimed to use acoustic telemetry to estimate natural mortality across a range of size classes and explore the effect of size class, season, and location on mortality rates. An acoustic receiver array was deployed in rivers of Van Diemen Gulf, Northern Territory, Australia. Detections from 185 sharks between 2013 and 2024 were converted into capture histories, which were used to calculate yearly and monthly estimates of mortality. Data demonstrate that river sharks experience high rates of mortality. Younger individuals had significantly higher rates of mortality, with G. glyphis and G. garricki neonates experiencing average yearly mortality rates of 0.898 and 0.731, respectively, compared with 0.120 and 0.233 in subadults/adults. Although mortality was highly variable temporally, over months and years, there were no significant differences between seasons, years or location, and there was no significant difference between species. Results indicate that river sharks in Van Diemen Gulf likely have very limited capacity to recover from population decline and are therefore vulnerable to environmental change and anthropogenic threats. Population monitoring and habitat management is critical to ensure the persistence of river sharks into the future.

One-third of all elasmobranchs (sharks and rays) are threatened with extinction. Euryhaline and estuarine generalist elasmobranchs are a group of 29 species that occupy non-marine environments during particular life-stages. These species are poorly known and disproportionately threatened, with 72.4% at risk of extinction or Data Deficient. A detailed knowledge of a species’ life history characteristics, movement ecology, habitat use, and population structure are required for the implementation of appropriate management and conservation measures. To date, research on euryhaline and estuarine species has lagged behind marine species. Here, a literature review and gap analysis of the euryhaline and estuarine species was conducted to identify gaps in 14 key parameters required for management. Of the 29 species, only the Bull Shark (Carcharhinus leucas) and the Largetooth Sawfish (Pristis pristis) had detailed information on a majority of parameters assessed. Nine species lack information on most parameters, while the Broadnose Wedgefish (Rhynchobatus springeri) lacks information on all but one of the parameters investigated. There is a high level of understanding of age- and size-at-maturity, size-at-birth, and growth for only five species, while nine species have estimates of natural mortality. Comprehensive reproductive biology data is unavailable for six species. Both short- and long-term movement ecology is well-understood for only two species, and habitat use for six species. Population structure has been studied in only eight species. Data on key life history parameters, population structure, and habitat requirements of the euryhaline and estuarine elasmobranchs are urgently required to develop appropriate management strategies and to secure populations.

Streams play a key role in the global carbon cycle. The balance between carbon intake through photosynthesis and carbon release via respiration influences carbon emissions from streams and depends on temperature. However, the lack of a comprehensive analysis of the temperature sensitivity of the metabolic balance in inland waters across latitudes and local climate conditions hinders an accurate projection of carbon emissions in a warmer future. Here, we use a model of diel dissolved oxygen dynamics, combined with high-frequency measurements of dissolved oxygen, light and temperature, to estimate the temperature sensitivities of gross primary production and ecosystem respiration in streams across six biomes, from the tropics to the arctic tundra. We find that the change in metabolic balance, that is, the ratio of gross primary production to ecosystem respiration, is a function of stream temperature and current metabolic balance. Applying this relationship to the global compilation of stream metabolism data, we find that a 1 °C increase in stream temperature leads to a convergence of metabolic balance and to a 23.6% overall decline in net ecosystem productivity across the streams studied. We suggest that if the relationship holds for similarly sized streams around the globe, the warming-induced shifts in metabolic balance will result in an increase of 0.0194 Pg carbon emitted from such streams every year.

Carbon capture, utilization, and storage (CCUS) technologies are being developed to address the increasing CO 2 emissions, mitigating the global warming and climate change. In this context, chemical precipitation has been advanced to enhance the performance, energy-efficiency and profitability of CCUS. In this review, we first present the fundamentals of precipitation and dissolution, and then summarize the incorporation of precipitation in each aspect of CCUS. The controlled precipitation of CO 2 -rich solid during the capture of CO 2 by regenerable solvents can reduce the energy demand. The mineral carbonation of silicate and industrial waste sequestrates CO 2 as stable solids. The efficiency of mineral carbonation, either direct or indirect, is dictated by the dissolution of minerals and the precipitation of carbonates and silica. The precipitation of calcium carbonate can be controlled to produce various polymorphs and morphology, enabling its utilization for the enhancement of profitability and environmental benefits. Ultimately, the prospective for future research was proposed.

Rivers in tropical Australia are largely pristine, and ecosystem connectivity is intact, but water resources in northern Australia are under increasing development pressure. A better understanding of the role and life histories of key migratory species is urgently needed to manage the risks posed by development. We investigated the life history of Macrobrachium spinipes (Schenkel, 1902) in the Daly River of the Northern Territory, Australia. We carried out a 13-mo trapping program (2011–2012) at 7 sites along the river between 92 and 405 km from the estuary. We provide the first detailed account of spatial and temporal changes in relative abundance and reproduction, and present information on length at first maturity and Fulton’s body condition factor. Reproduction was strongly seasonal and was restricted to the wet-season months of November to April, followed by a recruitment pulse 3 to 4 mo later during the early dry season. Length at first maturity declined as the reproductive season progressed but did not vary significantly with distance from the estuary. Condition was temporally variable and peaked for both sexes immediately after the wet season before declining throughout the dry season. Relative abundance patterns followed a similar pattern. Contrary to results for other Macrobrachium species in rivers of comparable length, we found an increase in the relative abundance of females throughout the river’s length during the reproductive season and reproductive effort occurring far upstream, over a restricted time period. This result highlights the importance of maintaining connectivity for reproductive success of this species and further recruitment into these upstream reaches.

Whether communities respond smoothly or discontinuously to changing environmental conditions has important consequences for the preservation and restoration of ecosystems. Theory shows that communities may exhibit a variety of responses to environmental change, including abrupt transitions due to the existence of alternate states. However, there have been few opportunities to look for such transitions in nature. Here, we examine the impact of a two-orders-of-magnitude decrease and then increase in planktivore abundance in Wintergreen lake (Michigan, USA), caused by the extinction and reintroduction of two dominant fish species (largemouth bass, Micropterus salmoides, and bluegill, Lepomis macrochirus). Over a 16+ yr period of slow change from high planktivory to low planktivory back to high planktivory, the zooplankton community changed smoothly and predictably between states. In years of low planktivory, the zooplankton assemblage was dominated by a single, large, cladoceran species, Daphnia pulicaria, whereas in years of high planktivory, D. pulicaria disappeared and was replaced by a suite of small-bodied cladocerans. We quantified the multivariate change in zooplankton community dissimilarity and found that community state smoothly tracked changes in planktivore density in both a forward and backward direction. Thus, there was little evidence of discontinuity in this system where transitions are strongly driven by planktivory.

Northern Australia contains the continent’s largest number of intact river systems, but these are facing increasing pressure as the proposed development of multiple and large-scale industries, including onshore gas, mining, horticulture, and agriculture, accelerates. These developments will require the diversion or extraction of large amounts of water and increase the risk of contamination by industrial and agricultural chemicals. There is an urgent need to collect baseline biophysical information on these aquatic systems before major developments proceed. Much community concern has been expressed about the potential environmental impacts of a developing shale gas industry (fracking) in the Beetaloo Sub-basin and upper Roper River region of the Northern Territory. Here we describe the first major survey of the freshwater fish fauna of this region and an assessment of the importance of groundwater in supporting fish biodiversity. This region is remote from major human settlements and the waterbodies are often difficult to access. Accordingly, we maximised the information we collected from limited sampling sessions by using both traditional fish survey methods (netting and electrofishing) and eDNA analysis of water and benthic sediment samples. Water column eDNA doubled the number of species recorded to those obtained from traditional survey methods alone. We found that the fish fauna was richest at sites on northward-flowing groundwater-dependent rivers. More work is needed to fully understand the dependence of individual species on groundwater inflows. However, it is evident that conserving freshwater fish biodiversity in these rivers will require protection of the groundwater resources to ensure baseflows and aquatic refuges persist through the most extended of dry seasons.

In the Australian wet–dry tropics, seasonal changes in hydrology can influence abiotic conditions and consequently influence standing stocks of benthic biomass and production. While there is some understanding of these processes at riverscape scales, effects of seasonal hydrology on benthic biomass and production in low-order streams remain largely unquantified. We observed changes in water quality, algal and macroinvertebrate biomass, and stream benthic primary productivity over a 15-month period in three low-order streams with contrasting flow regimes in the wet–dry tropics of northern Australia. Water quantity and quality showed a distinct seasonal signature reflected in seasonal peaks in algal (maximum 1.29 µg cm⁻²) and macroinvertebrate biomass (maximum 0.24 g m⁻²), and productivity (maximum 0.41 g C m⁻² days⁻¹). In particular, transitional periods between dry and wet seasons were key times of elevated production and algal biomass. Overall, variation in biomass and benthic primary production was greater between seasons than among streams indicating that extrapolation between seasons may not be appropriate.

Variation in the intensity of predation across the well-known environmental gradient of freshwater habitats from small, ephemeral ponds to large, permanent lakes is a key factor in the development and maintenance of aquatic community structure. Here, we present data on the distribution and abundance of four species of Chaoborus (Diptera: Chaoboridae) across this environmental gradient. Chaoborus show a distinct pattern of species sorting when aquatic systems are divided into fish and fishless environments, and this pattern is consistent with species traits known to influence their vulnerability to fish predation (i.e., pigmentation, diel vertical migration [DVM] behavior, and body size). To test whether fish are the drivers of this pattern, we created a gradient in fish density by stocking bluegill sunfish (Lepomis macrochirus) into 15 experimental ponds in southwestern Michigan, USA, and then allowed Chaoborus species to colonize. There was clear evidence of species sorting along the predation gradient; Chaoborus americanus was most abundant in the fishless ponds, C. flavicans was neutral in response to fish, and C. punctipennis and C. albatus were most abundant at high fish biomass, a response consistent with their field pattern. Furthermore, prey preference experiments confirm that size selective predation and differences in Chaoborus species traits contribute to the pattern of Chaoborus abundance and distribution.