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(2017)ThesisBiogeographic studies of South American mammals have typically shown a mismatch between latitudinal trends of extant and extinct mammal richness. South America shows modern mammal biodiversity increasing towards the Equator, whereas evidence of extinct South American mammals is concentrated at higher latitudes. Consequently, most studies focusing on the ecology and evolution of the South American mammal fauna have been limited temporally (to either extinct or extant taxa) or spatially (specific localities or ecosystems only). In this study, new methodologies were implemented to include both extinct and extant taxa in analyses of two orders of South American mammals: the Sparassodonta and the Chiroptera. A novel multivariate statistical approach was used to study the endemic metatherian order Sparassodonta and to test several competing hypotheses about the extinction of this group. Non-competitive ecological interactions within the South American mammal assemblage appear to have been the main drivers for sparassodontan extinction rather than, as commonly assumed, the result of competition and/or abiotic fluctuations. Diversity loss and eventual demise of the sparassodontans was a gradual process that followed family-specific patterns which changed over time. New statistical tools were also developed to examine phylogenetic diversity and phylogenetic endemism spatially and temporally in New World chiroptera. Trans-continental migrations proved to be most significant in the evolution of the South American bat fauna. Multiple centres of significant endemism were found across the New World for most bat families, extending the hypothesis of dual centres of diversification, previously proposed for Emballonuridae, Phyllostomidae and Mormoopidae, to Molossidae and Vespertilionidae. Central America and southern North America played particularly important roles in the diversification of New World bats, as did the Andes in South America.
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(2017)ThesisApex predators shape ecosystems through top down pressures which impact lower trophic levels through numerous interaction pathways. Lizard assemblages in arid Australia are driven by habitat structure, competition, and predation. The presence of mammalian predators in an ecosystem may influence the distribution of lizard species in Australian ecosystems. As lizards are ectotherms they are particularly sensitive to the changes in the thermal environment facilitated by climatic fluctuations, rainfall, herbivory and fire. The links between dingo control and lizard assemblages were explored using a natural experiment created by the Dingo Barrier Fence. Five years of data on predator activity and lizard assemblages from locations with a variety of management practices was used. The results showed that lizard assemblages reflected the differences in predator abundance and vegetation structure on either side of the Dingo Barrier Fence. Further investigation suggested a model where dingo control affects the abundances of lizard species via complex 4-link cascades. These findings suggest that there are winners and losers when dingoes are controlled: small lizards and geckoes benefit from dingo control while larger predatory lizards benefit from having dingoes in the ecosystem.
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(2015)ThesisThe impacts of nutrients discharged from intensive shrimp farms on receiving waters and sediments in Indonesia are poorly understood. The main objective of this study was to evaluate the distribution of nutrients originating from an intensive shrimp farm in the adjacent waters and sediments. Samples were collected in February 2011 and August 2011 to represent wet and dry seasons respectively. Sampling involved collecting pond effluent from sluice channels during the shrimp harvest from three ponds. Samples of water and sediments in the bay were collected downstream of the farm outfall at varying distances to seaward. Harvest strategies consistently influenced variations in concentrations of solid nutrients only such as TOC, TSS and chlorophyll a rather than dissolved nutrients measured in the wet and dry seasons. Higher precipitation in the wet season diluted NO2-N, PO4 and TOC which resulted in lower concentrations of these nutrients. Nutrients originating from non-points sources represented 92 and 98% of annual amounts of N and P, respectively. In this study, spatial variations in concentrations of nutrients in waters and sediments were mostly observed in the dry season when shrimp farms were the main source of nutrients entering the bay. The incoming freshwater in the wet season not only transports nutrients, it also dilutes them in Hurun Bay resulting in lower salinity and concentrations of TAN, NO3-N and PO4 observed in the wet season. The hydrology of Hurun Bay affected distribution of nutrients in the sediment as shown by sparse distribution of nutrients in the sediments. Concentrations of nutrients discharged from harvested shrimp pond and in Hurun Bay waters exceeded the concentration thresholds set by the Indonesian Government for shrimp pond effluent and marine biota, respectively. Therefore, improvement in shrimp farm management, such as feeding strategies that reduce waste, become a critical issue at this study site. In addition, better wastewater treatment for non-point sources and shrimp farm effluent before their wastewaters are released to this bay are suggested. Thus, integrated pollution control policies are needed to safeguard water quality of Hurun Bay.
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(2015)ThesisAs a major coastal process and hazard, rip currents are a topic of considerable interest from both a scientific and safety perspective. Collaborations between these two areas are a recent development, yet a scientific basis for safety information is crucial to better understanding how to avoid and mitigate the hazard presented by rip currents. One such area is the field of swimmer escape strategies. Contemporary safety advice is divided on the relative merits of a ‘Stay Afloat’ versus ‘Swim Parallel’ strategy, yet conceptual understanding of both these strategies is largely based on an idealised model of rip current morphology and flow dynamics where channels are incised in shore-connected bars. Two field studies of swimmer escape methods were conducted in NSW, Australia, making use of Lagrangian flow measurements and GPS-equipped swimmers to determine the viability of escape actions in rip current systems differing from this idealised model. At North Cronulla Beach two rip current systems were observed, with a rhythmic detached bar system compared to a current incised in shore-welded transverse bars. The detached bar system was found to produce long duration floats that were unsuccessful as an escape mechanism, and presented a distance-based hazard to those seeking to swim out of the system. At Bulli Beach, a topographic rip current in the lee of a headland was measured, with a Stay Afloat strategy, aided by strongly recirculating flow, producing rapid escapes and a high success rate. Of note in both studies, a newly tested Swim Onshore strategy was also found to be highly successful, with potential implications for future study and safety campaigns. The results of these studies are synthesised with the existing literature to produce a conceptual model of escape viability linked to morphological beach state, finding a decreasing gradient of escape viability with increased wave energy, and hypothesised negative outcomes for swimmers of limited ability in most scenarios, with implications for future safety education and research.
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(2015)ThesisExtensive mapping, petrological data and geochemical analyses shed new light on the environment of deposition of cherty sedimentary rocks that contain Earth’s oldest stromatolites in the c. 3.5 Ga Dresser Formation, North Pole Dome, Western Australia. Some researchers have interpreted a quiet shallow water evaporitic setting and others a tidal flat, but detailed stratigraphic and petrographic data supports deposition within a developing volcanic caldera that was flushed by voluminous hydrothermal fluids. A series of stratigraphic profiles measured on either side of the Dresser (barite) Mine over a distance of seven kilometres display true sediment thickness variations across active growth faults, as previously noted. Rapid lateral facies variations and diverse depositional settings, as well as multiple newly discovered eruptive layers of felsic volcaniclastic material support a volcanic caldera setting. Importantly, the first discoveries of geyserite and tourmaline-bearing ferruginous laminates interpreted as radiogenic, B-rich hot spring crusts are documented, providing evidence of emergence of the volcanic landsurface. Geyserite consists of alternating K-Al clay-rich (light) and anatase-rich (dark) laminae, 20 µm thick, that appear identical to modern geyserite formed from alternating acidic and alkaline fluids. Morphologically variable stromatolites, including domical, stratiform and coniform varieties, are restricted to shallow water environments, but are widespread within the lower parts of the succession, suggestive of phototrophs. Spatially more restricted occurrences of dendritic microbialites are overlying large hydrothermal veins, suggestive of chemoautotrophs. The deposition of stromatolitic rocks is inferred to have developed as a response to uplift of the surface during emplacement of a subvolcanic magma system that drove geysers and erupted ash. Subsequent caldera collapse formed deeper basins accompanied by coarse clastic sedimentary rocks in which there are no visible signs of life. Results support a diverse microbial community in these ancient rocks that were able to utilise energy sources from a variety of habitats within stages of a developing volcanic-hydrothermal system.
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(2018)ThesisField portable X-ray fluorescence spectrometers (fpXRF) are routinely used to provide real-time in-situ geochemical analysis for a number of elements. This study investigates the use of fpXRF to map the distribution and extent of metal contamination in soils at the abandoned Sunny Corner Ag-Pb-Zn (-As) mine using organs of Pinus radiata. The mine site is located approximately 200 km west of Sydney. Dispersion from outcropping mineralized rocks, contamination from mine tailings, AMD waters that continually feed into Daylight Creek have resulted in elevated Cu, As, Pb and Zn in soils, sediments and stream waters, with elevated contents detectable up to 25 km downstream Samples of P. radiata organs (needles, twigs and bark) were collected in a traverse extending away from the mine site into the surrounding hanging wall metasediments, as well as a denser sampling semi-grid over the actual mine site. Samples were analysed ex-situ after drying and milling. Quality control was established using an organic reference material and analysis of ashed samples using both fpXRF and ICP-MS. The data were determined to be fit-for-purpose for most key mineralisation-related elements (Fe, Mn, Cu, Zn), with poor data quality for As and Pb. Substantial differences were detected between the contaminated areas and background sites in all organs and for most elements, with the highest geochemical contrast in the needles. The patterns mimic the soil geochemical patterns to varying extent, with the strongest correlation being for Zn. There is high correlation between different organs for various elements indicating that the signal is unrelated to dust (not directly) but uptake by the trees from the soils and groundwater. Field-portable XRF has been demonstrated to provide rapid analysis of various trace elements in vegetation and, while the analytical work was conducted in the laboratory, their effective use in-situ is likely. Further application of fpXRF will be made to identify plant species that may be suitable metal bio-accumulators for mine site rehabilitation and restoration of the soil environmental quality of other metal-contaminated sites in Australia.
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(2017)ThesisArtificial reefs are increasingly used in offshore environments by natural resource managers as a tool to enhance recreational fishing, restore natural habitats, increase fisheries production and as tourist attractions for diving and surfing. As the footprint of individual or multiple structures can be large, an improved understanding of their ecological impacts on the surrounding environment and their performance as reef habitat is necessary. In this research two types of steel artificial reef were investigated: one a designed reef to enhance recreational fishing, and the other a large naval ship sunk as a diving attraction. Both reefs were deployed at 30 – 40 m depth on a soft bottomed, sandy seabed off the East Coast of NSW, Australia. The composition of benthic infauna, sediment characteristics, and demersal fish foraging were investigated around the designed reef, while the development of sessile and fish assemblages were studied over 5 years on the sunken ship. Around the designed reef, localised impacts on the infaunal composition (within 15 m) and the intensity of fish benthic foraging (within 30 m) were evident. Physico-chemical sediment characteristics did not, however, vary with distance from the structure. Fish foraging (rather than sediment properties) is the likely mechanism driving this ‘halo’ pattern of benthic infauna. Colonisation of the sunken ship by sessile biota and fish species was rapid within the first 6 months. Sessile assemblage composition became more homogeneous 1-3 years post sinking, before again diversifying between 3-5 years. Fish species richness also increased rapidly within the first 6 months and was still accumulating after 5 years. Both surface orientation and depth influenced the composition and development of the sessile assemblage through time. These studies reveal that the impact of a large, steel structure on the surrounding soft sediments and fish activity will be spatially constrained and that sessile assemblages on artificial reefs will be spatially and temporally heterogeneous, varying over the structure itself and over several years. Such findings provide useful insights to assist managers in the planning, design and assessment of new artificial reefs through improved understanding of their sphere of influence and spatio-temporal heterogeneity.
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(2019)ThesisMarine ecosystems globally are being directly impacted by multiple climate-mediated stressors, including: gradual ocean warming, an increase in the frequency and intensity of marine heatwaves (MHWs) and changes to ocean circulation such as the strengthening of western boundary currents. These stressors not only directly affect individual species but also indirectly impact ecosystem structure and function by altering species interactions. Changes to species interactions are partly driven by shifts in species distributions. For example, warming and strengthened currents are facilitating the poleward movement of tropical herbivores into temperate reefs by opening up thermally suitable areas poleward and increasing poleward larval dispersal. In Australia’s temperate Great Southern Reef, this has already strengthened some herbivore- kelp interactions in some regions and contributed to the loss of kelp, the reef’s main foundation species. Warming stress can also alter the algal microbiome, which in turn influences algal health, and there is the potential that this may affect changes in kelp-herbivore interactions by altering kelp palatability. This thesis aimed to gain further insight into the indirect effects of climate change stressors on the dominant kelp, Ecklonia radiata, by investigating the complex interplay of kelp-herbivore-microbe interactions. Firstly, I investigated the effects of ocean warming and MHWs on the kelp microbiome and on kelp susceptibility to herbivory. I aimed to understand if changes in the kelp microbiome influence interactions between kelp and a potentially range-shifting tropical herbivore, the sea urchin Tripneustes gratilla. Secondly, I used a bio-physical model to investigate climate-driven changes in dispersal of T. gratilla, to determine potential impacts on the urchin’s biogeographical range and on its interactions with kelp. I discovered that warming and MHWs increase kelp palatability and shift the microbial community of kelp towards larger abundances of microbes associated with disease and macroalgal degradation. Modelling forecasts indicate that T. gratilla is likely to expand its range poleward and create strengthened interactions with kelp. Overall, I discovered indirect future threats to Australia’s dominant kelp by forecasting strengthened kelp-tropical herbivore interactions and decreased resilience of kelp to grazing under warming and MHW conditions.
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(2019)ThesisSituated in the Boomarra Sub-basin, Hazel Creek is a moderately sized locality in the Toolebuc Formation, defined by fossiliferous slabs of flaggy limestone. In the mid-late Albian, the area was likely a shallow marine estuary, placing it uniquely close to shore. Due to this shallow depth and proximity to shore, the fauna is incredibly diverse. Among the marine invertebrates are the bivalve genera Aucellina and Inoceramus, the common belemnite genus Dimitobelus, and the ammonite genus Myloceras. Vertebrate remains are dominated by disarticulated fish bones and shark teeth (e.g. species of Cardabiodon, Echinorhinus, Richmondichthys, Pachyrhizodus, and an undescribed species of lizardfish) as well as rare fragmentary remains of chimeroids (Ptykoptychion tayyo). Marine turtles (Notochelone costata) are also common, represented by numerous pieces of shell and limb bone. Large marine reptiles like plesiosaurs (Elasmosauridae) and ichthyosaurs (Platypterygius australis) have also been recovered as isolated vertebrae, teeth, and limb elements. However, of greater significance are the previously undocumented terrestrial taxa that were washed in from the nearby shore. These elements allow us a singular glimpse into the terrestrial fauna of Australia in the mid-Cretaceous. Small, fragile limb bones of birds have been preserved, although poor preservation states limit identification and description. Of unique import, a mammal premolar has also been discovered, making Hazel Creek the only Mesozoic mammal locality known for northern Australia. This tooth represents the oldest mammal in northern Australia. This unique shallow marine locality holds promise of future discoveries which could shape our understanding previously undocumented terrestrial taxa and the Australian Cretaceous ecosystem.