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Mesoscale ocean eddies are commonly formed ocean habitats in the western Tasman Sea off the east coast of Australia. Ocean eddies form distinct ecosystems with elevated, or depleted productivity compared to the surrounding waters in a region that supports several ocean fisheries that are currently managed in real time by fisheries permits based on sea surface temperature and other satellite derived features that have been related to fish populations, but more details on the variable food-web parameters of ocean eddies would greatly benefit ecosystem based dynamic management strategies. I investigated two contrasting ocean eddies in the western Tasman Sea during September 2017, a cyclonic and anti-cyclonic eddy, using a size-based approach and stable isotope analysis of 15N, to identify a normalised biomass size-spectra (NBSS) and significant linear relationships between trophic level and body-size from primary producers to mesopelagic fishes. After correcting for differences in ẟ15N of Particular Organic Matter (POM, at the base of the food web), I derived estimates of predator prey mass ratios (PPMR), food-chain lengths (FCL), and trophic transfer efficiencies (TE) for each of the eddy food webs. The biological community within a cyclonic eddy had a higher enrichment of ẟ 15N resulting in increased trophic level with body-size when compared to an anti-cyclonic eddy. This resulted in a PPMR that was 7.5 times larger in the cyclonic eddy, and a TE that was approximately half as efficient than the contrasting anti-cyclonic warm-core eddy. Comparisons of two warmer water in the northern Tasman Sea eddies, with two similar eddies in the cooler waters to the south showed that the northern eddies influenced by tropical waters and the EAC had PPMRs 2.5-3 times larger than the eddies with the same rotational direction in the Tasman Sea. Furthermore, estimated trophic transfer efficiencies of both anti-cyclonic eddies were approximately double that of the cyclonic eddy in th

Yellowtail kingfish (Seriola lalandi, Valenciennes 1833; YTK) farming is considered the greatest opportunity for aquaculture expansion and diversification in Australia. Consequently, the demand for pelleted feed is expected to increase significantly for this species. Nutritional research on YTK has focused on macronutrient requirements and testing alternative protein and lipid sources to fishmeal and fish oil. However, there is a lack of information on micronutrient requirements and their effects on the growth and health of YTK. Therefore, it is important to acquire more knowledge on this topic to optimise the feed formulation for YTK. Choline is an essential nutrient typically supplemented in aquafeed and is abundant in raw materials such as fishmeal and soybean meal. Substituting raw materials for alternative food sources without knowing the choline requirement or its role in YTK performance might hinder YTK production. Accordingly, the main aim of this thesis was to improve our understanding of dietary choline on the growth performance and liver health of juvenile YTK at sub-optimal water temperatures. Liver was selected as a target organ because it is one of the major sites that facilitates various metabolic processes, including choline metabolism, and is susceptible to choline-deficiency induced liver disease. This thesis further explored the efficacy of using naturally-occurring stable isotopes to better understand the interactive effects of dietary choline and water temperature on nutrient assimilation of YTK. The aim was achieved and addressed by conducting two independent experiments with a series of interlinked studies. The research first determined the digestible choline requirement of YTK using a dose-response approach. The choline supplementation of a practical diet formulation at two temperatures (16 °Cand 24 °C) that bracket the culturing water temperatures commonly experienced by farmed YTK in Australia was also conducted. The digestible choline requ

2020 Elsevier Ltd Carbon mitigation services provided by coastal wetlands are not spatially homogeneous, nevertheless are commonly described on the basis of vegetation distribution within the intertidal zone. Distribution of mangrove and saltmarsh varies in response to frequency of tidal inundation, resulting in environmental gradients in edaphic factors that influence vegetation structure, and subsequently affect sedimentary carbon additions by vegetation and carbon losses by decomposition. Current sampling approaches and reporting do not adequately account for variability of carbon storage within a wetland, and assessments need to capture spatial variation associated with carbon storage to improve estimates of potential carbon mitigation services by natural ecosystems. This study quantifies the variation in near-surface carbon storage (i.e. upper 30 cm) across an intertidal gradient using a stratified sampling approach that recognises vegetation structure. Vegetation distribution and structure, as well as sedimentary controls on carbon content, explained variation in carbon storage. Saltmarsh near-surface carbon storage varied considerably between structural form. This was less evident for mangrove structural forms (i.e. tall, shrub, dwarf), which may be due to mangrove roots extending to depths beyond 30 cm. Sedimentary characteristics correlated with carbon content, demonstrating considerable influence on near-surface carbon storage within a wetland. The principal finding of this study was that variation within a wetland corresponds to the variation between sites. Stable carbon isotopes offer a means to identify previous vegetation contributions to sediment, associated with an earlier stage of wetland development, likely reflecting previous environmental conditions. A stratified sampling approach that recognises vegetation structure provides the capacity to account for variability of carbon within a wetland that is inadequately described by current sampling prot

In this study we compared ecosystem trophic structure between a tropical mangrove forest at Matang, Malaysia, and a temperate mangrove forest near mangrove poleward limits at Towra Point in south-east Australia. These forests are separated by 8500 km of ocean over 45° of latitude and are of contrasting size, productivity and diversity. However, we observed a marked degree of similarity in food chain length (approximately four trophic levels in both forests), the taxonomy of key intermediate members of the food chain and the isotope signature of primary carbon sources, suggesting a strong contribution of surface organic matter rather than mangrove detritus. Common families were represented among dominant grazing herbivores, zooplanktivorous fishes, decapod crustaceans and top predators. These similarities suggest that there is some consistency in trophic interactions within two mangroves on opposite sides of the Indo-Pacific, despite a degree of evolutionary divergence in the assemblage.

Groundwater is a vital resource. It contains 97% of unfrozen water on the planet, playing a key role in present and future water needs for humanity. However, our knowledge about the ecosystem functioning is very poor, and groundwater environments are increasingly exposed to anthropic impacts and climate change related processes. Novel biochemical (e.g. isotopic ecology) and genetic (e.g. eDNA) techniques, widely employed in fresh surface water studies, have the potential to unravel the complex dynamics shaping subsurface ecosystems, providing new insights to the small but quickly growing field of groundwater ecology. Stygofauna, together with microbes, are crucial actors in shaping and maintaining the organic matter (OM) cycles in environments characterized by low energy and scarce carbon availability. In order to understand groundwater ecological patterns, we investigate calcrete stygofaunal shifts linked with contrasting rainfall periods (low rainfall (LR), dry season; high rainfall (HR), wet season), through an interdisciplinary design composed of hydrology, isotopic ecology and genetics. Our results indicate that the inflow of rainfall under HR is responsible for increased nutrient concentrations in the system and dissolved organic carbon (DOC) pulses from the surface. Both the meiofaunal and stygofaunal communities’ benefit from these organic inflows, with gamma and proteobacteria the biota that fuels carbon and nutrients to the higher levels of the trophic web. The HR regime - and its subsequent terrestrial carbon incorporation - triggers a cascade effect driven by microbes (OM processors) and amphipods (biofilm grazers), which is finally transferred to the aquatic beetles (top predators). Overall, and in line with other work in the same research area, the inflow of rainfall triggered shifts towards more deterministic dynamics, revealing a complex web of interactions in a seemingly simple environmental setting. This study provides a preliminary untangling of t

Mangrove ecosystems store large quantities of organic carbon for long periods of time. This study explores organic carbon stock change through the first comparative study of radiometric analysis and repeat field measures over a multi-decadal period in a mangrove system. Examining one tall gallery forest of Avicennia marina, and an adjacent interior scrub mangrove of mixed Avicennia marina and Aegiceras corniculatum, radiometric analysis estimated a soil organic carbon accumulation rate of 4.3 ± 0.6 Mg C ha−1 y−1 in the tall gallery forest and 2.2 ± 0.5 Mg C ha−1 y−1 in a stunted mangrove. Repeat measures of root carbon separated by 30 years estimated an increase of 5.06 Mg C ha−1 y−1 in the tall forest and 6.63 Mg C ha−1 y−1 in the stunted forest-suggesting an underestimate of carbon accumulation by radiometric dating of 15% and 67% in the tall and stunted forest, respectively. A higher carbon stock in the interior forest was attributed to root mass increase, associated with landward mangrove encroachment. Extrapolated to the entire region of NSW we estimate that mangrove encroachment has contributed at least about 1.8 Tg C sequestration over the 70 years for which this has been observed in New South Wales, Australia.

We monitored coastal wetland vertical accretion, elevation gain and surface carbon (C) at Homebush Bay, Australia over 18 years (2000-2017) in three settings initially characterized by saltmarsh, mixed saltmarsh-mangrove ecotone and mangrove-dominated zones. During this time, the saltmarsh transitioned to mixed saltmarsh-mangrove ecotone, and the mixed saltmarsh-mangrove ecotone transitioned to mangrove, consistent with vegetation transitions observed across the east Australian continent in recent decades. In spite of mangrove recruitment and thickening in the former saltmarsh zone, and the dominance of mangrove root material as a contributing C source, the rate of C accumulation in the former saltmarsh zone did not change over the study period, and there was no significant increase in surface elevation. This contrasted with the response of sites with a longer history of mangrove colonization, which showed strong accretion and C accumulation over the period. The result suggests that the C accumulation and surface elevation gains made as a result of mangrove colonization may not be observable over initial decades, but will be significant in the longer term as forests reach maturity.