Science

Publication Search Results

Now showing 1 - 10 of 16
  • (2016) Sun, Melanie
    Thesis
    Healthy sediment communities are considered highly beneficial for aquatic ecosystem health. Sediments act as sinks for allochthonous materials and may buffer impacts through complexation and adsorption. As such, sediment dwelling organisms are susceptible to stress from compounds stored in the sediments. Factors that influence taxa-compound and inter-taxa interactions can impact important sediment functions. While biogeochemical implications of such impacts have received great attention, understanding the biotic changes that drive most of these functions remains elementary. Using high-throughput sequencing, this thesis investigates the influence of abiotic factors in anthropogenically modified estuarine systems on the relationship between sediment organisms and their potential function. Taxonomic (16S and 18S rDNA sequencing) and functional (amo-based diagnostic microarray) approaches independently found a significant association between anthropogenic activity and changes in sediment community structure across eight southeast Australian estuaries, ranging from relatively pristine to modified states. However, the complex interactions between multiple stressors in natural environments impede our efforts to disentangle the influence of common toxicants (e.g. metals, PAHs) and nutrients (e.g. total organic carbon) on sediment communities. In a replicated field experiment, we therefore focused our attention on sediment community responses to organic enrichment—a common contemporary stressor. Paired metagenome and metatranscriptome sequencing revealed functional shifts between control and organically enriched sediments. Anoxia, toxic sulphide production, lower primary productivity and decreased nitrogen metabolism were favoured under organic enrichment. Ammonification was the primary route of nitrogen removal. These all have negative implications for ecosystem health. Compositional shifts reflected functional attributes, with putative links identified between ammonia oxidation and Crenarcheota, methanogenesis and Methanosarcina taxa, and sulphate reduction and Desulfovibrio taxa. This research highlights the powerful insight gained when both compositional and functional aspects of community structure are viewed in concert.

  • (2012) Cassidy, Elizabeth
    Thesis
    Morphological variation is a result of complex interactions between physiological constraints, selection pressures and ecological conditions. All of these factors are vital in the understanding of the evolution of morphological adaptations. In this thesis, I examine three aspects of the phenotypic plasticity and morphological variation in two species of neriid flies, Telostylinus angusticollis and Telostylinus lineolatus. Chapter one examines allometric constraints on the diversification of populations. Static allometry slope is generally thought to constrain adaptation and diversification. We examined the diversification of static allometry by manipulating larval nutrient concentration and comparing allometric slopes in sexual and non-sexual traits across populations. We found evidence of slope diversification within T. angusticollis and T. lineolatus in a sexual trait. Our results suggest the diversification of static allometry slope can be driven by sexual selection. Following this, chapter two discusses sexual selection and its impact on diversification in males and females. Using reaction norms for nutrient concentration in a range of sexual and non-sexual body shape components, we identify different patterns of morphological diversification between the sexes. In addition to this, the patterns of diversification seen in males suggest that sexual selection is acting upon male body shape as a whole, rather than specific morphological traits. We consider the ecological and selective forces contributing to the diversification of the sexes. Chapter three examines another aspect of larval ecology, group relatedness, and its benefits or disadvantages. We find that fly larvae gain an advantage from being housed with closely related individuals, and emerge larger as adults, congruent with the kin selection hypothesis. These three chapters outline some of the different factors contributing to morphological variation and highlight the importance and complexity of phenotypic plasticity.

  • (2021) Hinchliffe, Charles
    Thesis
    Since Johan Hjort first proposed his ‘critical period’ hypothesis in the early 1900’s, fisheries scientists have recognised the importance of the early-life stages of fish in determining year-to-year variation in recruitment. Despite this, our ability to forecast larval success remains limited. This is particularly true in the Australian context, where larval fish monitoring programs have only recently been established. This thesis aims to contribute knowledge regarding the population dynamics of larval fishes off eastern Australia. To achieve this, I utilise a new larval fish assemblage database, develop new modelling techniques, and conduct three sampling voyages to test my models on original data. The work is presented across 4 independent research chapters. In Chapter 2, I characterise patterns in the distribution of larval fish over 15° of latitude with highly variable conditions driven by the East Australian Current, using a newly available larval fish database supplemented with recently collected samples. Along eastern Australia, generalized additive models reveal that larval abundance and diversity is higher in the north and decreases poleward for most of the year, establishing a baseline trend for the region. This pattern reverses in summer, when spawning events occur around Tasmania, which could change as the East Australian Current strengthens with climate change. Existing methods for estimating mortality rates, such as catch-curves, require large sample sizes, as they work by grouping individuals into age bins to determine a frequency distribution. Yet, sampling enough larvae is often not possible at fine scales within the constraints of research projects. Drawing on size distribution theory, and improved computational techniques, in Chapter 3 I develop a novel method to simultaneously estimate growth and mortality of fish larvae which improves certainty in estimates with fewer fish available. Using Bayesian inference methods, I show how growth and mortality can be estimated from a continuous distribution of sizes removing the need to bin data. Furthermore, these new models are flexible and can estimate non-linear growth and mortality functions. The ratio of larval growth to mortality, or its inverse, is used to indicate changes in cohort biomass and is referred to as a cohort’s “recruitment potential”. Most studies observing this metric have focused on variation at survey-level or annual scales, which may ignore crucial variability in cohort success at finer spatiotemporal scales relevant to individual larvae. By sampling larval Pacific sardine (Sardinops sagax) off southeast Queensland, in Chapter 4 I demonstrate that vital rates of cohort success vary at scales smaller than features that are generally considered to be oceanographic habitats (i.e., eddies and shelf waters). While growth rates are more consistent among features, rates of mortality are highly variable, highlighting the importance of incorporating mortality estimates in attempts to understand cohort success in field studies. Building on the understanding that size-spectra are remarkably consistent in marine ecosystems, in Chapter 5 I test the hypothesis that the slope of the plankton spectra provides a valuable diagnostic tool for rapidly assessing growth and mortality of larval fishes in situ. To test this, I sampled larval Pacific sardine and plankton simultaneously on three voyages along eastern Australia, using a bongo net with an interior finer-mesh net. Contrary to expectations, results from this study demonstrate a negative relationship between the slope of plankton size spectra and recruitment potential of larval Pacific sardine of equivalent size. This may result from high susceptibility of larval Pacific sardine to predation, owing to the thin body shape and poor swimming ability characteristic of clupeid larvae. Several stronger relationships between larval growth and mortality, and physical oceanographic parameters were evident. Together, these results indicate that years where spawning occurs predominantly in shelf areas with a lower concentration of large predatory zooplankton, and, the East Australian Current is meandering further from the shelf break than normal, could provide the necessary conditions allowing for exceptional levels of Pacific sardine recruitment off eastern Australia. My thesis suggests plankton size spectra are unlikely to reflect recruitment potential directly, at least for Pacific sardine. However, incorporating some size-based aspects of the plankton community into a broader modelling framework could further our ability to determine how larval success varies across a seascape. Improvements in the resolution of vital rate estimates, and of spatially explicit modelling procedures, might accurately predict larval success although data is currently unavailable. Therefore, continued sampling larval fishes and estimation of vital rates is required. While data from international programs such as CalCOFI provide a strong starting point, continuation of larval fish monitoring programs in Australia will provide an avenue to further explore forecasting of larval success

  • (2019) Ledet, Janine
    Thesis
    Global climate change is predicted to affect ecosystem functions and alter crucial interactions among species. While extensive research has been done on individual species across a range of stressors, less is known on how community responses to climate stressors are context dependent and vary across timescales. Responses may alter among individuals, by effects on interactions with other species, or with recent exposure to stress in an organism’s lifetime or that of previous generations. In this thesis, I measured the response of marine invertebrate assemblages associated with macroalgae to climate stressors, focusing on factors that may alter the magnitude or direction of climate effects. Subtidal macroalgae provide habitat for diverse communities and dominate temperate reefs worldwide. These habitats are some of the most vulnerable to climate stress, with the invertebrates associated with macroalgae critical to ecosystem function. Initially, I measured the combined effects of temperature and diet quality over two generations of the marine amphipod, Sunamphitoe parmerong. When provided their preferred diet, S. parmerong had greater survival at increasing temperatures that contributed to a larger potential population size, an effect not found on other alternate diets. Next, I considered effects of extreme temperatures on the survival of species within the epifaunal assemblage of the brown alga Sargassum across two seasons. Taxa were tolerant to extreme temperatures within the range of a heatwave, however, shifts in species composition between seasons suggests that the timing of stress is crucial. Using S. parmerong as a model, I determined whether trans- and multigenerational effects of prolonged temperature stress could influence individual traits and population survival. The fecundity of offspring from heat-stressed mothers was reduced, with no improvement of brood sizes found after three generations of increased temperatures. While thermal tolerance was greater in heat-stressed populations, further tolerance was not gained over multiple generations. Lastly, I measured how short-term acidification stress altered community composition and abundance. The most abundant taxonomic groups were tolerant to short-term acidification. Overall, factors relevant to ecological context altered assemblage-level outcomes under future climate conditions, emphasizing the need to incorporate these factors in climate research.

  • (2016) Lau, Ronda
    Thesis
    This research was about how life history traits were influenced by the nutrient components in the juvenile diet. The aim of this study was to provide more understanding about the function and the purpose of nutrients consumption. The first chapter addresses how essential and non-essential amino acids in the juvenile diet influence the juvenile performance and adult morphological traits. The second chapter addresses the effects of additional vitamin E in the protein-unrestricted juvenile diets on adult fitness and longevity. Both chapters had used Telostylinus angusticollis, neriid flies as the experimental organism. This was because this species is exceptionally plastic in adult morphology to its larval diet. The experimental larvae in the first chapter were raised in the nutrient-poor diet with the combination of extra essential amino acids, non-essential amino acids and sugar. The adult body size and relative head, antenna, wing and foreleg length were boosted by the presence of extra essential amino acids while the relative hind leg length was not affected, but the cost of such benefit was the decrease of larval viability. In contrast, the viability was significantly reduced to almost none by the non-essential amino acids. This may be caused by the large change in pH associated with the addition of non-essential amino acids. The development time was not affected by either essential or non-essential amino acids. The larvae in chapter two were raised in treatments with three levels (1, 3, 5μg/mL) of vitamin E and the presence of an additional amount of protein to the nutrient-poor base diet in the first experiment. The larvae in the second experiment were raised in treatments of the nutrient-poor base diet with the addition of 3μg/mL of vitamin E and the poor base diet as the control. The first experiment provided little evidence of a vitamin E by protein interaction. The second experiment showed that vitamin E itself had a positive effect on body size, but this effect was dependent to the sterilization of the larval environment. The presence of vitamin E in the juvenile diet decreased adult longevity and activity, especially in males. Nonetheless, it did not have any effects on juvenile development time, adult relative head length and adult relative antenna length. In conclusion, the effect of amino acids and the effect of vitamin E on life history traits were complex, indicating a need for further study.

  • (2017) Gibson, Alyssa
    Thesis
    The early-life environment can have profound effects on offspring development and behaviour into adulthood. There are physiological and behavioural trade-offs associated with altered developmental strategies as a result of responding to environmental cues. Oxidative stress, a physiological mechanism that can lead to decreased reproductive output and increased aging, has also been suggested to be a main consequence mediating investment in life-history traits, particularly reproductive effort. I aimed to examine the effects of developmental environments on reproductive effort and oxidative stress in young wild-derived mice, Mus musculus domesticus. I also examined age-related differences in sexual signalling and aggression in young adult and old male mice. I altered the early-life environment by manipulating litter size or introducing social cues in wild-derived mice and measured developmental and reproductive traits as well as markers of oxidative stress. Pups from enlarged litters suffered higher oxidative challenges compared to those from reduced litters. Male young exposed to male scents also exhibited lower levels of markers indicating oxidative stress, although this result was not consistent through all assays examined. However, males from enlarged litters and those exposed to female cues increased investment in sexual signalling, irrespective of potential increased oxidative challenges. Mothers exposed to male cues during pup rearing decreased maternal care at peak pup development age. Interestingly, male young exposed to male cues at weaning age suppressed their growth rate, whereas those that were raised with male cues from birth grew at a faster trajectory, possibly as a result of altered maternal care. When examining differences in reproductive effort between older and younger adult males, older males scent marked more frequently and were significantly more aggressive, although they had lower major urinary protein levels than younger adult males. Interestingly, both young and old males scent marked more frequently after competitive encounters regardless of the outcome. While I did find evidence of oxidative stress potentially mediating reproductive effort, especially in offspring from experimentally enlarged litters, it did not explain all the differences in reproductive effort measured. I also found that the early-life environment had significant impacts on growth and traits linked to reproductive investment post-weaning, especially in male mice.

  • (2017) Birrer, Simone
    Thesis
    The development of coastal areas often results in the introduction of a suite of contaminants to these highly productive systems. Contaminants accumulate in soft sedimentary environments where they may affect resident microorganisms responsible for driving major biogeochemical cycles and providing a range of ecosystem services. The cumulative effects of multiple contaminants can impact both the structure and function of microbial communities. These cumulative effects are not yet well understood, however they have potential repercussions at local, regional and global scales. Microbes are inherently difficult to study as the majority cannot be cultured in the laboratory. Modern molecular techniques enable the study of microbes at a genetic level. Targeted gene sequencing and meta-omics provide snapshots of community structure and function. However, their application as biomonitoring tools is still in its infancy. In this thesis, I investigate targeted sequencing for ecosystem health assessment and assess metatranscriptomics as a new biomonitoring tool. I use experiments and surveys to test the value of molecular techniques in informing ecosystem-wide consequences of structural and functional changes. Targeted sequencing revealed that bacterial communities are more sensitive to multiple disturbances than eukaryotes (traditionally used for biomonitoring) and are potentially better indicators of ecosystem change. Metatranscriptomics proved to be a sensitive, reliable and replicable tool, which provided rapid, ecologically relevant, information. Sediment communities exposed to metals and organic enrichment had significantly altered gene expression profiles that may reflect accumulation of toxic compounds and increased production of greenhouse gases. Surveys revealed that sediment communities impacted by legacy contaminants had reduced primary productivity and greater potential for community fracturing, which itself may lead to lower productivity and lower remediation capacity. Molecular approaches generated information that could revolutionise biomonitoring approaches. However, the lack of extensive genetic reference libraries and complex data processing requirements continue to pose challenges to the routine adoption of these techniques. My research highlights the power of molecular approaches for assessing ecosystem health and the consequences of urban contaminants on community structure and function.

  • (2013) Morgans, Courtney
    Thesis
    My thesis aimed to investigate the influence of selection on an animal invading a novel habitat and how subsequent differences in natural selection, sexual selection and genetic drift might influence phenotypic variation among populations. The Pacific leaping blenny on Guam (Alticus arnoldorum) provided a novel opportunity to address these aims as it has made one of the most extreme ecological transitions possible, it is a fish that lives its entire adult life on land. Furthermore, the presence of multiple populations of this fish around the island allowed the investigation of how differences in selection pressures and gene flow might generate or limit phenotypic variation between populations that otherwise occupy the same broad habitat type (intertidal rocks on land). First, I examined the influence of natural selection in the form of predation on colonising a novel environment (here, a shift onto land). The colouration of male and female blennies from five populations was examined along with the colour of their respective backgrounds. I found the body colour of all populations closely resembled the habitat on land. A subsequent predation experiment confirmed that this background matching functioned to reduce predation and was therefore adaptive. These results suggested that closely resembling the colour of habitat backgrounds has probably aided the Pacific leaping blenny in successfully colonising land. Second, I examined the relative influence of natural selection (predation), sexual selection and gene flow on phenotypic variation among populations on land. Results suggested that variation in natural selection and sexual selection had a predictable influence on phenotypic expression: sexual selection has promoted the exaggeration of ornaments, while natural selection has reduced the conspicuousness of these features. Most notably, this population divergence in ornamentation has occurred despite high gene flow. Overall, my thesis demonstrates how adopting an integrative approach is essential for isolating the mechanisms leading to phenotypic divergence during the invasion of new environments, and how populations can subsequently diverge in response to variation in social factors and predation once colonisation has occurred.

  • (2014) Pease, Ceiwen
    Thesis
    Contamination is a ubiquitous problem in the marine environment that has been observed to cause negative effects on multiple scales. Contamination may interact with other co-occurring stressors in natural systems further complicating the understanding of contaminant effects in the natural environment. Exposure to contamination via diet may also alter contaminant toxicity, due to varying uptake rates between different food sources. This thesis examines the effects of diet-borne contamination and other frequently encountered stressors, as well as their interactions, on herbivores that live on and consume macroalgae in near-shore rocky reefs. The relationship between temporal and spatial variation in macroalgal copper contamination and associated herbivore assemblages was assessed in a one-year field survey of Port Jackson (Sydney, Australia). Decreased herbivore abundance was associated with increased copper concentration; however, this relationship was only observed during peak abundance periods and was highly species-specific. The persistence of herbivores at even the most contaminated sites suggested the possibility of local adaptation and this was subsequently explored for an abundant herbivorous amphipod. Using a quantitative genetics approach genotypes from 8 locations were tested for copper tolerance. While many of the criteria for local adaptation were met, no evidence of local adaptation was found in this species. Copper toxicity is highly dependent on the species of macroalgae consumed, as indicated by a significant interaction between these two factors. A synergistic effect of exposure to copper contamination and temperature was observed at 26 ºC, with decreased amphipod survival observed. Exposure to algal secondary metabolites did not appear to interact with copper contamination; however the efflux transporter, P-glycoprotein, is a good candidate for the regulation of both chemical stressors. In summary algal-herbivore interactions are complex and driven by differential bioavailability of copper amongst macroalgal species. Persistence of herbivores at contaminated locations may be due to regulatory mechanisms such as P-glycoprotein however more research in this field is required.

  • (2015) Henschke, Natasha
    Thesis
    Pelagic tunicates, including salps, are an important category of gelatinous zooplankton and yet are relatively understudied. Salps regularly occur in intermittent swarms and can quickly become the most dominant zooplankton within an area. My thesis explores the trophic interactions of salps within the zooplankton community using stable isotope analysis, the environmental drivers of salp population dynamics, and the occurrence of salp deposition on the sea floor. The trophic niche of salps within the oceanic zooplankton community was investigated using stable isotopes of carbon and nitrogen. Zooplankton and suspended particulate organic matter (POM) were sampled in three different water types: inner shelf (IS), a cold core eddy (CCE; cyclonic) and a warm core eddy (WCE; anti-cyclonic). Recent upwelling in the IS water type resulted in lower than expected trophic enrichment for all zooplankton species (0.53 compared to 3.4 ), and the salp Thalia democratica was depleted in 15N compared to POM. Trophic enrichment of zooplankton within the CCE (2.74 ) was higher than the IS, and more similar to expected results (3.4 ). Based on chlorophyll a and nitrate concentrations, the WCE was characterised as an oligotrophic environment and was associated with an increased trophic level for omnivorous zooplankton (copepods and euphausiids) to a similar level as carnivorous zooplankton (chaetognaths). This study shows that trophic relationships among the zooplankton are dynamic and can vary across water types. The demographic characteristics of three salp swarms were studied to examine factors influencing variations in salp swarm magnitude. The interannual abundance of Thalia democratica during spring was related to the rates of asexual reproduction (buds per chain). T. democratica abundance was significantly higher in October 2008 (1312 individuals m-3) than 2009 and 2010 (210 and 92 individuals m−3, respectively). Salp abundance was negatively related to buds per chain and relative growth rates, implying a faster release rate. As T. democratica abundance was significantly positively related to food >2 μm in size and negatively related to the proportion of non-salp zooplankton, salp swarm abundance may depend on the abundance of larger phytoplankton (prymnesiophytes and diatoms) and competition with other zooplankton. A discrete-time, size-structured Thalia democratica population model was developed to investigate the temporal resolution of a salp swarm. The model used size-dependent reproduction and mortality, where growth was dependent on food consumption (chlorophyll a biomass) and temperature. Average generation time (12 days) and mean abundances of each stage correspond to previously reported values. Salp ingestion rate and the doubling time of chlorophyll a were the most influential parameters, negatively influencing salp biomass and abundances for each individual stage. Forcing the model with a 10-year temperature and chlorophyll a time-series identified that salp abundances off the coast of Sydney (34ºS) were significantly greater during spring and summer compared to autumn and winter. This is consistent with observations of salp swarms which occur after the spring phytoplankton bloom. Salp swarm abundance appears to be related to the availability of food (chlorophyll a per salp) rather than absolute abundance (chlorophyll a biomass). Mass depositions of the large salp Thetys vagina were observed on the Tasman Sea floor in 2008 and 2009, prompting examination into the potential of salp carcasses to act as food fall events to the benthos. Over 1700 carcasses were identified on the sea floor and benthic fish and crustaceans were observed feeding on the carcasses. Analysis of a 30-year trawl survey database determined that salp biomass (wet weight, WW) in the eastern Tasman Sea regularly exceeds 100 t km−3. T. vagina has a carbon (31% dry weight, DW) and energy (11 kJ g−1 DW) content more similar to that of phytoplankton blooms, copepods and fish than to that of jellyfish (cnidarians), with which they are often grouped. Given their abundance, rapid export to the seabed and high nutritional value, salps are likely to be a significant input of carbon to pelagic and benthic food webs, which until now, has been largely overlooked.