Australian freshwaters have relatively low water hardness and different calcium (Ca) to magnesium (Mg) ratios compared with those in Europe. The hardness values of a substantial proportion of Australian freshwaters fall below the application boundary of the existing European nickel biotic ligand models (Ni BLMs) of 2 mg Ca/L. Toxicity testing was undertaken using Hydra viridissima to assess the predictive ability of the existing Ni BLM for this species in extremely soft waters. This testing revealed an increased competitive effect of Ca and Mg with Ni for binding to the biotic ligand in soft water (<10 mg CaCO /L) than at higher water hardness. Modifications were made to the Ni BLM by increasing the binding constants for Ca and Mg at the biotic ligand to account for softer waters encountered in Australia and the more important competitive effect of Ca and Mg on Ni toxicity. To validate the modified Ni BLM, ecotoxicity testing was performed on 5 Australian test species in 5 different natural Australian waters. Overall, no single water chemistry parameter was able to indicate the trends in toxicity to all of the test species. The modified Ni BLMs were able to predict the toxicity of Ni to the test species in the validation studies in natural waters better than the existing Ni BLMs. The present study suggests that the overarching mechanisms defining Ni bioavailability to freshwater species are globally similar and that Ni BLMs can be used in all freshwater systems with minor modifications. Environ Toxicol Chem 2018;37:2566-2574. © 2018 SETAC.

The bioaccumulation of mercury in the food webs incorporating the major piscivorous fish species of Lake Murray, Papua New Guinea, has been characterised. Methylmercury concentrations increased with trophic level and the proportion of total mercury present as methylmercury increased from <1% in plants to 94% in piscivorous fish. Methylmercury bioaccumulation factors (BAFs) were similar to those found in temperate environments, with a typical increase of 1 log unit between planktivore and piscivore trophic levels. The greatest bioaccumulation of methylmercury occurred between seston and the water column (log BAF of 5.36). The bioaccumulation of mercury to levels of regulatory concern by the lake's piscivores was attributable to the biomagnification power of the plankton-based food chain comprising four trophic levels (phytoplankton, zooplankton, planktivore, piscivore) rather than any elevated concentrations of mercury in waters or sediments. The methylmercury concentrations of individual piscivores were positively correlated with both trophic position, as indicated by δ15N measurements, and fish size. Stable-isotope measurements were used to identify fish species where dietary changes occurring with age significantly augmented age-related bioaccumulation of mercury.

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1. Development of effective conservation strategies for freshwater biodiversity must take account of the trade‐off between species preservation and human use of ecosystem goods and services. The latter cannot be prevented, and attempts to manage ecosystems that focus solely on maximizing biodiversity will fail. 2. A compromise position of management for ecosystem functioning and human livelihoods — rather than preservation of every species — will provide a better basis for biodiversity conservation. This has implications for the management of exotic species. 3. There are some situations, in lentic habitats in Sri Lanka, for example, where the establishment of exotics has increased fishery yields without apparent detriment to native biodiversity. The Sepik River in Papua New Guinea provides another illustration of potential compromises between human livelihoods and biodiversity conservation. 4. The Sepik supports a relatively unproductive fishery. Two fish stocking projects (in 1987–93 and 1993–97), representing a partnership between the Papua New Guinea Government and the United Nations (UNDP/FAO), led to the introduction of a suite of exotic fish into the Sepik. Species were selected on the basis of their potential to occupy niches not filled by native fish. Unfortunately, the outcomes of these introductions are poorly documented, although there is preliminary evidence both of increased human use of exotic fish as well as declines of some native species associated with the spread of exotics. 5. Better understanding of the results of the Sepik fish introductions is important, because the pressures of burgeoning human populations in most of tropical Asia make it impossible to preserve near‐pristine environments such as the Sepik. While attempts to conserve natural or near‐natural systems must remain a priority, there is a need to develop strategies for the management of damaged or degraded ecosystems, which may contain exotics, with the aim of maintaining ecosystem functioning and, if possible, maximizing the persistence of native biodiversity. Copyright © 2006 John Wiley & Sons, Ltd.

Nine pools were studied in an intermittent stream. They were close to each other but differed in size, substratum, amount of shade and duration of water presence. Initial conditions were set by wet season flooding, following which each pool developed its own character. Cluster analysis showed that communities changed substantially with time in both species composition and abundance, and that some initially similar communities diverged while some initially dissimilar ones converged.Principal Components Analysis showed that these community changes were due largely to the drying of the pools, and to seasonal effects. Specialised drying communities developed in the pools of longer duration (up to 8 months), but not in the short-lived pools (3-4 months). Apparently similar numerical responses in different pools were often caused by different suites of predominant species.The diversity of the fauna (total of 78 species) was high in comparison with similar habitats in non-tropical regions.The pattern of development of the pools' communities was much as expected from island biogeography theory, except that there was no relationship between species richness and duration and size of pools. The species complements were largely opportunistic, being governed by extreme environmental disturbance.