Bacteria-protozoa interactions are one of the oldest between prokaryotic and eukaryotic organisms. As such, their study offers a unique opportunity to understand the different relationships that have evolved between them, including pathogenesis, and how their interaction can affect some important processes, such as wastewater treatment. In the first part of the work described here, the grazing defence mechanisms employed by Pseudomonas aeruginosa against the surface grazer, Acanthamoeba castellanii, were investigated. P. aeruginosa cells from early logarithmic growth and stationary phase were found to use different defence strategies. The type-III secretion system (T3SS) was found to be responsible for cytotoxicity of early logarithmic growth cells against A. castellanii. Of the three exotoxins produced by P. aeruginosa PA99, the phospholipase ExoU was found to make the greatest contribution to bacterial toxicity against the amoebae. Interestingly, a PA99null mutant that does not produce any known exotoxins but synthesises a secretion apparatus, was also found to be toxic to the amoeba, suggesting that the T3SS was being used to translocate other unknown toxins. Quorum sensing regulated virulence factor production was found to be involved in the grazing defence response of stationary phase P. aeruginosa cells. A. castellanii was found to be most susceptible to hydrogen cyanide and elastase produced during late logarithmic and stationary phase. In the second part, a stable isotope probing method was developed to investigate carbon flow through bacteria-protozoa food webs in activated sludge. The method was subsequently used to track carbon from bicarbonate and acetate through bacteria-orotozoa food webs under ammonia oxidising and nitrate reducing conditions. It was found that the Peritrich ciliate Campanella umbellaria, dominated the acquisition of carbon from bacteria with access to CO2 under ammonia oxidising conditions. Thus it appears that some of these bacteria must live in the plankton, as C. umbellaria is a filter feeder. No specific protozoan groups were found to dominate carbon acquisition from bacteria with access to acetate, under nitrate reducing conditions, probably due to label dilution. Overall the results presented here showed how bacteria-protozoa interactions have shaped infectious processes in higher eukaryotes, and the dynamics of carbon flow in activated sludge.

The potential relationship between riparian arachnids and aquatic insect productivity was assessed in forest streams throughout the central South Island of New Zealand. Initially, a survey was conducted of thirty seven, first-third order forest streams. Streams were selected to represent a range of benthic invertebrate standing crops (as a surrogate measure of "productivity") from Banks Peninsula streams with relatively high benthic invertebrate densities to acid mine drainage streams near Reefton that were almost devoid of aquatic life. At each site benthic invertebrate densities and biomass were measured in riffle habitats and adjacent gravel bars were sampled for terrestrial invertebrates. At a sub-set of 16 sites, a 20 metre longitudinal web-building spider survey was conducted along each bank of the stream. As an additional component, a 20 metre transect starting at the stream margin and running perpendicularly into the forest was used to survey the density of web-building spiders with increasing distance from the stream. Results from the survey of in-situ stream insect biomass and gravel bar invertebrates showed a strong relationship between aquatic insect biomass and the biomass of riparian arachnids (R2 = 0.42, P < 0.001) having accounted for potentially confounding factors such as stream size, elevation, substrate and disturbance. The 20 metre longitudinal survey showed that streams with the highest in-situ insect biomass had significantly higher densities of web-building spiders along their banks (R2 = 0.28, P < 0.05), having accounted for potential confounding variables of elevation, habitat architecture and stream and channel width. The stream to forest survey showed a strong exponential decay in web-building spider densities with increasing distance from the stream (R2 = 0.96, P < 0.0001). Regardless of stream productivity web-building spiders were most abundant at the stream margins and rapidly declined to very low densities 20 metres from the stream. In order to further test the relationship between riparian web-building spider densities and stream insect productivity, a stream fertilization experiment was conducted on six first-second order streams in the Maimai experimental catchment, Reefton. Three streams were enriched by the addition of a fertiliser solution mainly consisting of sodium nitrate for seven months, and the other three streams were used as controls. Water chemistry, benthic invertebrate communities, emerging aquatic adults, and the densities of web-building spiders along the stream corridor and in the forest were monitored in three seasons (spring, summer and autumn) over the course of the nutrient-addition. By the end of the experiment, conductivity was significantly higher in nutrient-addition streams than in the control streams (F = 80.5, P < 0.001), but chlorophyll concentrations showed no significant differences between treatments. Both benthic mayfly densities (F = 6.15, P < 0.05) and the biomass of adult aquatic dipterans (Chironomidae, Simuliidae) (F = 9.25, P < 0.01) were significantly higher in nutrient-addition streams in the last sampling round. Spiders recorded from intercept traps indicated that by the end of the experiment spider activity was significantly higher within 2.5 metres of the nutrient-addition streams (F = 5.70, P < 0.01). However, seasonal densities of web-building spiders along the stream margin and in the forest decreased with no significant differences observed between nutrient-addition and control streams. The results from these studies indicate that adult insects emerging from streams represent an important source of prey that could influence the biomass and abundance of riparian arachnids. Additionally, the results imply that stream productivity and size could mediate the strength of the interaction between riparian and stream habitats. Moreover, feedback mechanisms present in both systems could have implications for such interactions. The elevated densities of web-building spiders observed at the stream margin led to the proposal of the "Highway Robber" hypothesis. This hypothesis suggests that such higher densities of spiders are the result of increased insect activity along the stream corridor: the emergence of adult aquatic insects was predicted to vary less over temporal and spatial scales than that of terrestrial insects due to the poorly synchronized life histories in many New Zealand stream insects. I conclude by suggesting that there are numerous anthropocentric perturbations such as loss of heterogeneity, introduced species, pollution and habitat degradation that could undermine and decouple the intimate linkages between aquatic and terrestrial ecosystems.

Food webs are structured by intricate nodes of species interactions which govern the flow of organic matter in natural systems. Despite being long recognized as a key component in ecology, estimation of food web functioning is still challenging due to the difficulty in accurately measuring species interactions within a food web. Novel tracing methods that estimate species diet uptake and trophic position are therefore needed for assessing food web dynamics. The focus of this thesis is the use of compound specific nitrogen and carbon stable isotopes and molecular techniques for assessing predator-prey interactions and energy flow in natural aquatic ecosystems, with a particular focus on the species links between phytoplankton and zooplankton. The use of δ15N amino acid values to predict organism trophic position are evaluated through a meta-analysis of available literature which included measurements from 359 marine species (article I). Through a controlled feeding study isotope incorporation in aquatic organisms, across both plant-animal and animal-animal species linkages is further assessed (article II). These studies showed that δ15N amino acid values are useful tools for categorizing animal trophic position. Organism feeding ecology influenced nitrogen trophic discrimination (difference in isotope ratio between consumer and diet), with higher discrimination in herbivores compared to omnivores and carnivores (article I). Nitrogen isotope trophic discrimination also varied among feeding treatments in the laboratory study (article II). The combined findings from articles I &amp; II suggest that researchers should consider using group specific nitrogen trophic discrimination values to improve accuracy in species trophic position predictions.  Another key finding in the controlled laboratory study (article II) was consistently low carbon isotope discrimination in essential amino acids across all species linkages, confirming that these compounds are reliable dietary tracers. The δ13C ratios of essential amino acids were applied to study seasonal dynamics in zooplankton resource use in the Baltic Sea (article III). Data from this study indicated that zooplankton assimilate variable resources throughout the growing season. Molecular diet analysis (article IV) showed that marine copepod and cladoceran species ingested both autotrophic and heterotrophic resources. Evidence from both articles III &amp; IV also revealed that zooplankton feed on a relatively broad range of diet items but not opportunistically on all available food sources. Mesozooplankton feeding patterns suggested that energy and nutritional flows were channelled through an omnivorous zooplankton food web including microzooplankton prey items. Overall the results of this thesis highlight that stable isotope ratios in specific compounds and molecular techniques are useful tracing approaches that improve our understanding of food web functioning. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Manuscript. Paper 4: Manuscript.</p><p> </p>

Climate changes affect species interactions which can have cascading effect up to the ecosystem level. This work investigates the effects of temperature and predator size on predator prey interactions by measuring the feeding rates of predators and metabolic rates of both predator and prey, using dragonfly larvae Aeshna cyanea and toad tadpoles Bufo bufo as a model system. Possible consequences of the findings for the impacts of climate change and predation on amphibian populations are discussed.

Arsenic transfers and toxicology are important topics of research and a public health concern because arsenicosis affects millions of people worldwide every year. One of the most significant sources of arsenic in the environment is industrial wastes, such as by-products of mining operation. In Yellowknife, Northwest Territories, Canada, there were two large gold mines—Giant Mine and Con Mine, along with dozens of small-scale mines. The combined by-product of emission from these roasters might have contributed to high concentrations of arsenic found in the city. This thesis presents the results of two related studies to address the environmental health concern: (1) to investigate the arsenic transfers and arsenic species accumulation in freshwater food webs near large legacy mining operations in Yellowknife, and (2) to assess the long-term health risk of inorganic arsenic exposure from the consumption of fish in Yellowknife among the general residents and the Yellowknives Dene First Nation. We found that inorganic arsenic is biominified in food webs (i.e. inorganic arsenic concentrations diminish at higher trophic positions relative to lower trophic positions). Higher-trophic organisms have low inorganic arsenic concentrations in tissue due to biotransformation of inorganic arsenic to non-toxic organic arsenobetaine, and effective elimination of arsenic from their tissue. The trophic positions of freshwater organisms can be used to predict the range of arsenic concentrations and its species composition, accounting for more than 80% of variance. Dietary study results show that the Yellowknives Dene First Nation consumed significantly more fish in their diets (adults: 19 g/day, children: 9 g/day) compared to the general residents of Yellowknife (adults: 9 g/day, children: 5 g/day). Our probabilistic risk assessments showed no significant long-term non-carcinogenic and carcinogenic health risks of inorganic arsenic exposure from fish consumption for the majority of Yellowknife residents, but elevated cancer risks among the adult heavy fish consumers in Yellowknife. However, our data suggested that the residents of Yellowknife were not exposed to higher cancer risks from inorganic exposure compared to the general population in Canada. Therefore, due to fish health benefits and the values associated with its consumption, fish should continue to be a major source of sustenance in Yellowknife.

Microplastic particles (MPs) are widely distributed in aquatic environments and present a potential risk to marine life. This thesis considers several issues relating to methodologies for sampling and analyzing MPs and the sources and fate of these particles in the marine environment, wild and farmed shellfish, and food webs of southern coastal British Columbia, Canada. Chapter 1 introduces MPs as a contaminant, methodologies for studying them, and reviews what is known about their source, fates, and ecotoxicology in marine environments. Chapter 1 also outlines the goals of this thesis. Chapter 2 compares the potential MP concentration estimates provided by two different seawater sampling methods. Jar samples filtered to 8-µm yielded MP concentrations averaging approximately 8.5 times higher than bucket samples filtered to 63 µm, per L of water (at the site level), driven largely by differences in the number of microfibres. An analysis of MP concentrations and mesh sizes reported in the literature suggests that using a 300–350-µm mesh may underestimate total MP concentrations by one to four orders of magnitude compared with samples filtered through much smaller mesh sizes (e.g., less than 100 µm), and despite the effect of sample volume. Particles less than 300 µm in diameter make up a large component of MPs commonly found in fish and invertebrates. As such, common sampling practices fail to adequately measure a biologically relevant class of MPs, thereby undermining the ability to quantify ecological risk. Chapter 3 determines the influence of shellfish aquaculture activity, and its use of plastic equipment, on MPs in bivalves and their environment by comparing MP concentrations in Manila clams (Venerupis philippinarum) and Pacific oysters (Crassostrea gigas) grown on commercial shellfish beaches with those grown on non-aquaculture beaches from six areas. MP concentrations in water and sediment were also determined in four of the areas. MP concentrations did not differ between shellfish aquaculture and non-aquaculture sites for either bivalve species or for sediment and water samples. Beach sediment type had a minor effect, with more gravelly or sandier beaches associated with higher MP concentrations in oysters or clams, respectively. Oysters on sites using many synthetic anti-predator nets had more MPs than those on sites without any plastic, but analysis of particles using Fourier-transform infrared spectroscopy suggested a predominance of textile fibres including nylon and polyester, which are not typically used in shellfish aquaculture. Chapter 4 uses stable isotope food web analysis and hierarchical Bayesian generalized linear mixed models to explore whether bioaccumulation and biomagnification are occurring in coastal marine food webs at three locations. Bioaccumulation was higher for smaller-bodied suspension feeding animals such as bivalves. However, biomagnification was not occurring in animal digestive tracts, and trophic dilution was demonstrated in fish livers. Trophic transfer was shown to occur between prey and predator for rockfish, but higher concentrations in full stomachs compared with empty ones suggested rapid excretion of ingested MPs. Chapter 5 supplies some general conclusions on the status of MPs in the British Columbian environment, as well as risks to seafood consumers. It also explores future work that will be needed to understand the complex ecotoxicology of MPs. / Graduate / 2022-04-12

Arctic tundra wetlands support abundant waterbirds, but invertebrate prey communities may change with climate warming. Increased influx of nutrients and labile dissolved organic matter (DOM) from thawing permafrost may alter the relative importance of organic matter (OM) sources, with associated changes in relative biomass of taxa dependent on different sources. In six wetland types, we used stable isotopes (δ13C, δ15N) to compare contributions of four OM sources (periphytic microalgae, cyanobacteria, macrophytes, and peat) to the diets of nine macroinvertebrate taxa. Relative OM contributions within invertebrate taxa were similar among wetland types. Cyanobacteria comprised only 2–7% of OM sources for all taxa in shallow wetland types (<1 m), but up to 25% for oligochaetes and Physidae in deeper wetlands. Macrophytes were minor OM sources (<13%) in all wetland types except deep open lakes (21–26%). Peat typically comprised 20–40% of OM sources except for Physidae (mostly 50–80%). Microalgae were the dominant OM source for most taxa (47–78%, mean ⁓60%), although less for Oligochaeta and much less for Physidae (9–32%). High periphyton production with very depleted δ13C values likely results from continuous daylight illuminating shallow depths, high N and P levels, and very high pCO2 derived from bacterial respiration of DOM leached from thawing permafrost. Invertebrate consumption of microalgae and peat appears often to involve bacterial intermediates. Impacts of warming on invertebrate prey availability will likely depend not on shifts in OM sources, but on changes in overall area or number of shallow ponds.

The cold water of Antarctica has a unique endemic fauna, where durophagous predators are rare or absent. Due to climate change the water is heating up and the predators have begun to return to the Southern Ocean, which could bring a lot of changes to the food web. There is a high risk it will lead to losses in the unique marine fauna of Antarctica. The aim of this study is therefore to examine the potential effect these invasive species has on the food web structure in the Weddell Sea. To study this, several general network metrics were used (connectance, number of interactions, vulnerability and generality, trait distributions), as well as a number of centrality metrics (betweenness, closeness, PageRank). The analyses showed that none of the invasive species become important in the Weddell Sea food web. Nor do they significantly change the food web structure in any way which impact the importance of the native species. Their great opportunism regarding their prey species, and thereby their connectedness and thus their position in the network, are probably the main reason why theses invasive species did not become important in this food web. The lack of changes in the food web structure due to the presence of these invasive species are probably also a result of not including factors such as abundances and network dynamics in the analyses, which seem to be the driving forces when it comes to changes in food web structure caused by invasion of species.

The Arctic is warming faster than any other region of the globe. To conserve and manage many thousands of lakes across arctic landscapes, scientists need to understand historic and present conditions within these lakes to predict how the lakes, and the organisms that inhabit them, may respond to a changing climate. The goal of my research was to improve our understanding of what physical, chemical, and biological factors contribute to: 1) how lake food webs are assembled; and, 2) how these food webs may change in the future. First, I used long-term observations and lab experiments to determine how fish food, including zooplankton and snails, may respond to a warming climate. I then used field measurements of arctic char (Salvelinus alpinus) body characteristics, genetic samples, and fish diets to investigate if, and potentially why, populations of arctic char across a series of lakes achieve different maximum body sizes. Finally, as a method of monitoring population-level changes of fish abundance, I collected samples of arctic char DNA in lake water to test if estimated arctic char population abundances within a given lake correspond to the amount of DNA collected. Fish will require more food to eat as their metabolism increases with warming lake temperatures. Based on a thirty-year period of record, I determined zooplankton abundance increases in warmer years, indicating there is likely to be enough food for fishes in the future. Accordingly, zooplankton and snail abundance and development was also faster in warmer treatments of my lab experiments. My field observations indicated these are important prey items for arctic char. Small arctic char eat more zooplankton and large arctic char eat more snails, and these observations were consistent whether or not other predators are found in the particular lake. Similarly, my analyses did not indicate morphological or genetic differences between small and large arctic char within the same lake, suggesting arctic char size structure is determine by biological characteristics, including primary productivity and arctic char density. Indeed, estimates of arctic char population abundances across a series of lakes followed a gradient of arctic char densities, and my DNA sampling corresponded with this gradient. As there are thousands of lakes across the Arctic, my research demonstrates lake food webs, and the fishes within them, are likely to adapt to a warming climate. However, biological, chemical, and physical properties of these lakes can vary widely such that management and conservation plans may need to be developed at relatively small spatial scales across a large landscape.

No description available.