Highly regulated salinity gradients in solar salt pond concentrating sequences provide an opportunity to investigate in situ salinity impacts on aquatic flora and fauna. The Shark Bay Salt solar ponds at Useless Inlet in Western Australia vary in salinity from seawater to four times seawater over the pond sequence. We observed a shift from planktonic to benthic primary productivity as salinity increased. Water column photosynthesis and biomass decreased markedly with increasing salinity, while benthic productivity increased as cyanobacterial mats developed. Correspondingly, productivity shifted from autotrophy to heterotrophy in the water column and from heterotrophy to autotrophy in the benthos. Both shifts occurred at intermediate salinity (S=110 g kg )1 , q=1.087 g cm )3 ) in the pond sequence, where there was little production by either. Within individual ponds, productivity, algal biomass and physico-chemical conditions were relatively constant over one year, with only water column photosynthesis significantly different between seasons, mostly due to greater winter production. Transitions between benthic and planktonic production and their relative magnitudes appear to be driven mostly by direct responses to salinity stress, but also by changes in nutrient availability and grazing, which are also influenced by salinity.

The aim of this research was to examine nutrient limitation of phytoplankton in solar salt ponds of varying salinity at Useless Inlet in Western Australia. These ponds use solar energy to evaporate seawater for the purpose of commercial salt production. A combination of techniques involving water column nutrient ratios, comparisons of nutrient concentrations to concentration of magnesium ions and bioassays were used in the investigation. Comparisons of changes in dissolved inorganic nitrogen to phosphorus ratios and concentrations of dissolved inorganic nutrients against changes in concentrations of the conservative cation Mg 2? indicated that phytoplankton biomass was potentially nitrogen limited along the entire pond salinity gradient. Nutrient addition bioassays indicated that in low salinity ponds, phytoplankton was nitrogen limited but in high salinity ponds, phosphorus limited. This may be due to isolation of phytoplankton in bioassay bottles from in situ conditions as well as to changes in phytoplankton species composition between ponds, and the variable availability of inorganic and organic nutrient sources. The differences in limiting nutrient between methods indicate that phytoplankton cells may be proximally limited by nutrients that are not theoretically limiting at the pond scale. Dissolved organic nutrients constituted a large proportion of total nutrients, with concentrations increasing through the pond sequence of increasing salinity. From the change in nutrient concentrations in bioassay bottles, sufficient dissolved organic nitrogen may be available for phytoplankton uptake in low salinity ponds, potentially alleviating the dissolved inorganic nitrogen limitation of phytoplankton biomass.

Mapped geographical distributions of many birds are an overestimation of their true range and this overestimation is particularly high for threatened species. Due to their restricted ranges, specialized habitats and inability to relocate to other areas, island birds are particularly vulnerable to anthropogenic effects on their habitats, but few studies have investigated the suitability of remaining habitat for species restricted to small oceanic islands. Here, we developed a fine-scale species distribution model to investigate the breeding habitat of the Lord Howe currawong Strepera graculina crissalis. Using 73 nest locations as occurrence records, we found that currawongs nest preferentially near creek lines at lower elevations in the forested areas of the island (maximum elevation of 120 m). Habitat suitability decreased rapidly as the distance to creeks increased, indicating that many forested areas far from a creek line were unsuitable habitat for nesting currawongs. Using a combination of Thiessen polygons and suitable habitat to define territory boundaries, we estimated the average territory size to range between 2.48 ha and 5.23 ha. Using a conservative threshold, our model identified 195 ha of Lord Howe Island's land area as highly suitable nesting habitat for the Lord Howe currawong, while using a less conservative threshold identified a further 246 ha as medium suitable habitat (441 ha total). Hence, we estimated that the island can support a maximum number of 84 breeding territories. This study shows that the Lord Howe currawong has a narrower ecological niche than was expected, lowering the carrying capacity for this species on the island. As birds on remote islands are often unable to relocate to other suitable areas, it is important to determine the remaining habitat to ensure the continued persistence and conservation of threatened island species.

Island species are susceptible to invasive mammals because of their small populations, specialised habitats and reduced likelihood of recolonisation. For more than 50 years, invasive mammals have been eradicated from islands around the world. Despite the success of eradications, there are few publications in the primary literature detailing the ecological benefits and consequences of these eradications. Here we conduct a review of the published literature focussing on rodent eradications conducted on Australian and New Zealand islands and we evaluate the extent of reporting of non-target mortality and ecological monitoring following an eradication. A search of the Database of Island Invasive Species Eradications website identified that successful, whole-island rodent eradications were conducted on 66 Australian and 124 New Zealand islands in the period from 1964 to 2016. We found that non-target mortality was rarely ever reported (3% and 12% for eradications on Australian islands and New Zealand islands, respectively). Results of any quantitative ecological monitoring following eradications were published for only 10% of all successful rodent eradications on Australian islands and 19% of all eradications on New Zealand islands. There also has been no change in reporting of potential benefits and consequences of rodent eradications in Australia and New Zealand over the last few decades despite an increased awareness of the problem of under-reporting. We discuss the detailed benefits and consequences of these eradications in Australia and New Zealand and highlight the need to incorporate ecological monitoring into new projects to document benefits and consequences of eradications to inform future eradications.

Some human-altered habitats such as saltfields support significant numbers of shorebirds and waterbirds, but their values in tropical eastern Australia are poorly understood. With the continuing loss of shorebird habitats in the East Asian-Australasian Flyway, identification of important habitats and management is important for their conservation. The habitat value of two saltfields associated with the Fitzroy River estuary, Queensland (23.520S, 150.860E) was evaluated by monthly surveys over 33 months and by comparison to previous surveys of nearby natural wetlands. Saltfields supported as many waterbirds and species as freshwater and naturally saline lagoons. Numbers of migratory shorebirds peaked during the southern migration period (September to November), when wetlands in tropical northern Australia are at their lowest extent, thus elevating the conservation value of tropical saltfields to shorebirds. Sharp-tailed Sandpipers were regularly present in numbers exceeding international levels for staging, while Red-necked Stints were just below the staging criterion. Salinity regime was found to influence waterbird communities associated with saltfield pools: piscivores dominating metasaline pools, and shorebirds hypersaline pools. A seasonal pattern of occurrence occurred in some guilds with greatest numbers in the drier months (cormorants, pelicans, ducks and egrets, all significantly negatively correlated with the previous month’s rainfall), most of which bred in nearby natural wetlands during the wet season. Furthermore, cormorants were abundant in the saltfields and fluctuated less compared with natural lagoons during the critical drier months. Overall, saltfields are an integral component of the ecology of the landscape, providing complementary resources to that of the natural wetlands.