Current trends toward warmer air temperatures and longer ice free seasons in Hudson Bay are expected to cause changes in Arctic marine ecosystem dynamics. Ringed seals (Phoca hispida) will likely experience changes in levels of predation, competition, and prey availability. The purpose of this thesis was to investigate seasonal, inter-annual, and spatial variation in Hudson Bay ringed seal feeding ecology. Fatty acid composition, δ15N, and δ13C varied significantly by season, suggesting seasonal changes in foraging habitat and diet. Spatial differences in ringed seal stable isotope ratios occurred between western and eastern Hudson Bay, and there was a strong relationship between spring air temperature and δ15N. Peak δ15N occurred within a range in spring air temperatures between approximately -5°C and -2°C. I propose that the high δ15N observed in ringed seals within this temperature range is indicative of relatively greater importance of capelin (Mallotus villosus) in the ringed seal diet.

Identifying the ecological mechanisms that determine food web structure is critical for understanding the causes and consequences of diversity. The objective of this thesis was to identify the mechanisms structuring aquatic food webs across environmental gradients from a multi-level perspective (individual to ecosystem) using integrative methodology and field experiments to test classic ecological theory. My results demonstrate support for the dynamic constraints hypothesis, which predicts habitats with greater disturbance should have shorter food chains, but are not consistent with the ecosystem size hypothesis that predicts larger ecosystems have longer food chains. Insect and amphibian richness increased with increasing pond size and hydroperiod, indicating that insertion of new consumers into pond communities was driving variation in food-chain length. A multivariate analysis testing the influence of physicochemical variables on food-web characteristics revealed that hydroperiod and pond area had a strong influence on amphibian and invertebrate assemblages, trophic diversity and 15N range. Food-chain length did not respond strongly to any one variable, but instead responded weakly to multiple environmental variables, suggesting interacting influences on food-web structure. Conversely, the trophic niche of amphibian larvae was not influenced by pond hydroperiod, but did exhibit ontogenetic diet shifts. Populations of amphibian larvae with broader niche widths also had increased individual variation, supporting the niche variation hypothesis. In addition, I assessed whether species diversity influenced the magnitude of cross-habitat resource flow between aquatic and terrestrial habitats via emerging aquatic insects, metamorphosing amphibians, and litter deposition. Deposition into ponds far exceeded carbon exported via insect and amphibian emergences. We found a negative relationship between resource flux and the diversity of amphibians and insects, which contradicts the general pattern of positive biodiversity-ecosystem function relationships. My research strongly suggests environmental variation is a key process in shaping food-web structure and function and that multiple methodologies are needed to understand temporal and spatial dynamics of aquatic ecosystems.

Submerged caves, locally referred to as cenotes, can be found throughout the Yucatan Peninsula of Mexico. These nutrient poor, aphotic “underground estuaries” lack photosynthetic primary productivity, but are often found underlying high primary productivity areas such as mangroves and tropical forests. Adjacent ecosystems contribute organic carbon to the cave systems via percolation, where it is then utilized by the obligate, cave-dwelling fish and invertebrates. Another potential pathway through which organic carbon can enter the cave food web is through chemosynthesis. Chemoautotrophic sulfur-oxidizing or nitrifying bacteria have been found in the hydrogen sulfide layer or in the sediments of some anchialine caves. Our study utilizes 13C/12C and 15N/14N stable isotopes as well as 14C radiocarbon dating to determine and compare the sources of organic matter entering a coastal anchialine cave (Cenote Aak Kimin) versus an inland cave (Cenote Maya Blue) in the Yucatan Peninsula. Stable isotopes have long been employed in tropic investigations. This study, however, is the first to utilize radiocarbon isotopes in anchialine caves. The use of both stable and radiocarbon isotopes as source indicators provides greater discrimination in systems that contain numerous carbon sources or indistinct trophic levels, particularly to distinguish between chemoautotrophic versus photosynthetically derived carbon. Results indicate that chemosynthetically derived organic carbon contributes substantially to the diet of some crustaceans, such as the stygobitic shrimp Typhlatya, while other species remain dependent on detrital inputs. Depleted δ13C values and aged radiocarbon values (as low as -47.51‰ and 1840 yrs. for Typhlatya spp.) in comparison to particulate and sediment δ13C values (lowest -32.07‰ and -28.43‰, respectively). A comparison of isotopic values between Cenote Aak Kimin and Cenote Maya Blue suggests that the trophic web of the coastal cave incorporates more photosynthetic or detrital carbon, while the inland cave, with more depleted 13C and 14C values, relies more heavily on chemoautotrophic carbon. Within both systems, however, distinct photosynthetic and chemoautotrophic levels were identified. Water quality parameters, especially dissolved oxygen and pH, support the hypothesis of bacterial activity at the halocline. Anchialine systems in the Yucatan Peninsula are threatened due to increases in tourism, development, and pollution. Quantifying and qualifying the inputs of organic carbon is vital for the management and conservation of the area’s freshwater resources.

Fast paced population growth in urban areas of southern Ontario is putting increased pressure on the surrounding aquatic environment. The City of Guelph uses the Speed River to assimilate its municipal wastewater effluent. With a projected 57% population increase in the watershed by 2031, the assimilative capacity of the river may be challenged in the coming years. The Guelph Wastewater Treatment Plant uses tertiary treatment methods greatly reducing ammonia, suspended solids and phosphate concentrations in the effluent. However there are still impacts detectable related to excessive nutrients released into this relatively small river (6th order) which promotes algae and aquatic macrophyte growth. There is also concern about a variety of emerging contaminants that may enter the river and impact the health of the ecosystem. The research in this thesis examined the seasonal and spatial variability and extent of the impacts of the wastewater effluent on the riffle fish communities in the Speed River. Stable isotope signatures (δ13C and δ15N) were used to understand the changes in the dominant benthic fish species, Rainbow Darters (Etheostoma caeruleum) and Greenside Darters (E. blennioides), relative to changes in invertebrate signatures and their abundance. Rainbow Darters were extremely abundant relative to Greenside Darters at the site immediately downstream of the effluent outfall, particularly in August. The benthic invertebrate community was distinctly different downstream of the effluent outfall, especially in the summer, with a reduced abundance of Elmidae beetle larvae and increased abundance of isopods (Caecidotea intermedius) compared to upstream. δ13C and δ15N of the two darters species were similar at all sites in May and July, but in August and October Rainbow Darter signatures were more enriched in the two heavier isotopes at sites downstream of the effluent outfall. The vast majority of invertebrate taxa sampled were also enriched at the downstream sites. An analysis of Rainbow and Greenside Darter stomach contents revealed that Rainbow Darters incorporated more isopods and other invertebrates in their diet, especially at the immediate downstream sites suggesting that they are more adaptable to the altered downstream environment. The feeding habits of Greenside Darters appear to change between July and August in response to changes in habitat and food availability. They are potentially consuming food organisms with less enriched isotopic signatures, which results in their isotopic signatures not rising during these months like most of the invertebrates and other fish. Alternatively, the Greenside Darters may move across the stream to feed on invertebrates that remain unexposed to the wastewater effluent. These impacts, although subtle, may be a reflection of the Speed River ecosystem being compromised by nutrient inputs from the wastewater effluent. With the impending increase in demand on the treatment plant (e.g., population growth), ongoing treatment and infrastructure improvements may be needed in the future to maintain the current ecosystem structure.

Thesis (M.S. - Hydrology and Water Resources)--University of Arizona. / Includes bibliographical references (leaves 118-121).

Thesis (Ph.D.)--McMaster University (Canada), 1991. / Source: Dissertation Abstracts International, Volume: 53-11, Section: B, page: 5618. Supervisor: Henry P. Schwarcz.

Thesis (Ph.D.)--University of Wollongong, 2006. / Typescript. Includes bibliographical references: p. 129-148.

Thesis (M.Sc. Biological Sciences)--University of Waikato, 2008. / Title from PDF cover (viewed February 25, 2009) Includes bibliographical references (p. 70-78)

Thesis (Ph. D.)--University of Hawaii at Manoa, 2003. / Includes bibliographical references (leaves 199-222).

Thesis (Ph. D.)--University of Nevada, Reno, 2008. / "December 2008." Includes bibliographical references. Online version available on the World Wide Web.