The production and use of manufactured metal (oxide) nanoparticles has exploded in recent years as they are exploited for their novel physical and chemical properties. Cerium oxide NPs (CeO2NPs) help increase combustion in diesel engines and their reported ability to scavenge free radicals has been exploited in therapeutic treatments. Silver NPs (AgNPs) are now used in consumer products such as socks and sticking plasters due to their antibacterial properties. Once released into the environment, their ultimate fate is predicted to be the oceans The aims of this thesis are to investigate the bioaccumulation and biological effects (oxidative stress and lipid peroxidation) of CeO2NPs and AgNPs on the mussel Mytilus edulis, and to understand the potential for trophic transfer of CeO2NPs to the crab Carcinus maenas, and subsequent induced biological effects. It was found in acute exposures that, at the suggested regulatory limit of 3mg/l, less than 5% of a CeO2NP dose will be accumulated by the digestive gland of M. edulis within 4 hours, before being depurated over at least 56 hours. There were no significant biological effects of CeO2NPs, yet larger, micron-size particles had significant anti-oxidant effects. Most effects were transitory, returning to normal levels after 24 hours. In uptake comparisons between AgNPs and Ag-nanorods (AgNRs) at 10μg/l (towards the regulatory limit of 1.9μg/l), AgNRs were accumulated in the digestive gland within 2 hours, but were depurated by 4 hours. Similarity in accumulation between AgNPs and ionic Ag – including continuous accumulation in the gills over 48 hours – suggested dissolution was mostly responsible for this. Both nanoforms instigated isolated oxidative stress responses over 4-24 hours, yet none were significantly worse than AgNO3, which instigated the greatest suite of significant oxidative stress responses. In trophic transfer experiments C. maenas accumulated CeO2NPs in the hepatopancreas at less than 1% of the fed dose. Stomach accumulation was high but transitory, with most particles removed in the faeces. Gills were also a site of accumulation and it was thought that the haemolymph provided a route of transit between the digestive organs and the respiratory organs. This novel experiment used NPs crafted from 140Ce; changes in isotopic ratios of Ce in the crab following trophic transfer could therefore be used to determine absolute increases in concentration against high, and highly variable, background concentrations. There were no significant biological effects following trophic transfer of these 140CeO2NPs. It was found that the current regulatory limits are predicted to be sufficient to protect M. edulis and C. maenas from acute exposure to CeO2NPs and AgNPs, yet chronic exposures should be investigated since the relationship between the uptake and elimination rate of NPs will determine the extent of bioaccumulation and biological effects.

There is ample evidence that climate change is impacting on phenology and it has been suggested that this may generate trophic mismatches. A key system for investigating phenology and trophic mismatch occurs in spring in temperate deciduous woodlands, where folivorous caterpillars and their predators, insectivorous passerines, are reliant upon ephemeral resources for reproductive success and survival. However, studies are primarily conducted within single-site, oak- (Quercus sp) dominated woodland and focus on a single caterpillar species, winter moth (Operophtera brumata), despite these passerines being habitat generalists with large geographic ranges. It remains to be seen whether insights gained from these studies can be generalised on the landscape scale across different habitats. In this thesis, I explore the extent to which geographic and habitat variation operates in this system and attempt to expand the system beyond a linear single-species food chain into a more biologically realistic multi-species food web. I also identify the most important environmental factors predicting the phenology of the passerines to allow better predictions of how their phenology could alter under future climate change scenarios. To address these questions, I established a novel 220km transect of Scotland incorporating 40 field sites that vary in elevation and the type of deciduous woodland habitat, monitoring six blue tit (Cyanistes caeruleus) nestboxes, tree and invertebrate phenology and abundance, at each site throughout the springs of 2014-16. Firstly, I assess how blue tit occupancy and productivity are affected by the variation in fine-scale woodland habitat, latitude, elevation and prey availability that exists along the transect (Chapter 2). I find that habitat variables strongly affect fledging success but not occupancy or clutch size, whilst occupancy exhibits biogeographic trends, revealing that the relationship between breeding decisions and outcomes differs among habitats and implies that it may be difficult to generalise results from one habitat to others. Next, I aim to identify the environmental aspects which play a role in regulating blue tit reproductive phenology by examining the ability of temperature, tree phenology, invertebrate prey abundance and photoperiod to predict nest initiation and laying dates (Chapter 3). I find that night-time temperature in early spring is the most important predictor of both nest initiation and lay date (slopes ~ -3days/°C) and I suggest that this supports the hypothesis that temperature acts as a constraint on timing rather than a cue. Invertebrate abundance is also a positive correlate of lay date, possibly allowing fine-tuning of timing. This knowledge provides clearer foundations from which to predict future phenological change and possible trophic mismatch in this system. There is the potential that the apparent effect of temperature on blue tit reproductive phenology is indirect and mediated by diet, which is largely undescribed in the period prior to breeding. Therefore, in Chapter 4 I examine how blue tit diet varies across habitat, geography and time, and whether there is a dietary cue utilised to initiate breeding phenology, using data from metabarcoding faeces collected from nestbox-roosting adults in early spring. Geographic variation in diet is substantial, with high site-to-site dietary turnover (β-diversity), as well as high turnover along the elevational and latitudinal gradients studied. Dietary α-diversity (richness) is unaffected by geographical variables, but increases over time, with significant pre-breeding dietary increases in Lepidoptera and Hemiptera signifying a possible cue. In addition, these data provide the most comprehensive next-generation insights into the diet of a wild bird to date and identify 432 prey taxa. Finally, I analyse how biogeographic and habitat variables affect the phenology, abundance and diversity of caterpillars (Chapter 5). Host tree species’ varied significantly in their likelihood of hosting a caterpillar, with oak and willow (Salix sp.) the most likely. Biogeography had less effect on the likelihood of caterpillar occurrence, but elevation delayed peak date by 3.7 days/100m increase. There was also support for the spring caterpillar peak being dominated by a few key species, with over half of all caterpillars identified being of just three of the 62 total species, including winter moth. These findings contribute to understanding how the temporal distribution of caterpillars varies across habitats on the landscape scale. Taken together, the findings of this thesis reveal considerable geographic and habitat variation throughout this system, in both the composition of the food web and the impacts on blue tit productivity, demonstrating why caution must be exercised when extrapolating findings from one location or habitat to others.

<p>Analiza ishrane je urađena na uzorcima 16 populacija vrste <em>Bufo bufo</em>, sa&nbsp;ukupno 356 adultnih jedinki. Od toga 8 uzoraka pripada podvrsti<em> B.b. bufo</em>-populacija sa 158, a 8 uzoraka <em>B.b spinosus</em> populacija sa 198 jedinki. Za analizu&nbsp;ishrane je kori&scaron;ćen i uzorak od 150 primjeraka, tek metamorfoziranih jedinki.&nbsp;Uzorci populacija su prikupljeni sa teritorije Srbije i Crne Gore. Ishranu ispitivanih&nbsp;podvrsta roda <em>Bufo</em>, na svim lokalitetima čine jedinke plijena isključivo predstavnici&nbsp;Invertebrata. Kod obje podvrste dominantan plijen su pripadnici reda Coleoptera i&nbsp;Hymenoptera kod <em>B.b. spinosus&nbsp;</em>(70,05%,16,92%), &nbsp;kod <em>B.b. bufo&nbsp;</em>(59,69%, 22,61%).&nbsp;Multivarijantna analiza urađena na ukupnom uzorku pokazujeda postoji statistički&nbsp;značajna zavisnost ispitivanih morfolo&scaron;kih karaktera žaba i promjenljive&nbsp;morfologije plijena. Korespodentna analiza je pokazala da jedinke obje &nbsp;podvrste&nbsp;preferiraju sličan plijen samo &scaron;to je učestalost tog plijena različita po podvrstama i&nbsp;polovima. Kod tek metamorfoziranih jedinki Anura na oba lokaliteta prisutan je isti&nbsp;plijen sa malim procentualnim razlikama. Prisustvo relativno visokog procenta&nbsp;Chironomidae ukazuje da ove jedinke nisu u potpunosti pre&scaron;le na terestrični način&nbsp;života. Dok prisustvo visokog procenta familija Formicidae i Byrrhidae ukazuje na&nbsp;<br />ishranu kojoj inače teže pripadnici vrste <em>B. bufo</em>, prelaskom na terestrični način&nbsp;života. Vrijednosti &scaron;irina trofičkih ni&scaron;a (B_A) po podvrstama pokazuju da je podvrsta <em>B.b. spinosus</em><i>&nbsp;</i>(B₁A=0,15) imala neznatno manju vrijednost u odnosu na podvrstu&nbsp;<em>B.b. bufo</em> (B₁A=0,16) , &scaron;to ukazuje na to da su pripadnici obje podvrste imale&nbsp;prilično ujednačenu ishranu. Na osnovu taksonomije plijena zabilježeno je veoma&nbsp;visoko preklapanje ni&scaron;a ishrane između podvrsta (95%). Veoma su oskudni&nbsp;literaturni podaci o ishrani ove dvije podvrste, &scaron;to podatke i rezultate ovog rada čini&nbsp;posebno vrijednim.</p> / <p>Diet analysis was conducted on the samples of 16 populations of species&nbsp;<em>Bufo bufo</em>, &nbsp;with total of 356 adult individuals. Among that, 8 samples belonged to&nbsp;sub-species <em>B.b. bufo</em> &ndash; population with 158 samples, and another 8 samples&nbsp;belonged to <em>B.b. spinosus</em>, with population of 198 individuals. For diet analysis we&nbsp;also used the sample of 150 individuals which have just finished metamorphosis.&nbsp;Population samples were collected from the territories of Serbia and Montenegro.&nbsp;The diet of investigated subspecies belonging to the genus <em>Bufo</em> from all localities,&nbsp;was composed of the Invertebrata exclusively. Coleoptera and Hymenoptera were dominant prey items in both groups <em>B.b. spinosus&nbsp;</em>(70.05%, 16.92%), and <em>B.b. bufo&nbsp;</em>(59.69%, 22.61%). Multivariate statistical analysis which was performed on the&nbsp;entire sample, showed existence of statistically significant dependence of&nbsp;morphological traits of common toadand variable morphology of prey. &nbsp;Correspondent analysis showed that individuals of both subspecies prefer similar&nbsp;prey, but the frequency of the prey occurance at different subspecies and sexes is&nbsp;different. Recently metamorphosed Anuran individuals from both localities, take&nbsp;the same prey with a small differences inpercentage. The presence of a relatively&nbsp;high percentage of Chironomidae indicates that these individuals are not completely&nbsp;moved on to terrestrial life. While the presence of a high percentage of the families&nbsp;Formicidae and Byrrhidae indicates a diet which usually species <em>B. bufo </em>aspire&nbsp;during the transition to terrestrial life. Values (B_A) of trophic niche width (B_A)&nbsp;indicate that the subspecies <em>B.b. spinosus&nbsp;</em>(B_A =15) had a slightly lower value&nbsp;compared to subspecies <em>B.b. bufo</em> (B_A =15) which indicates that both subspecies had&nbsp;a fairly uniform diet. Based on the taxonomy of prey, very high dietary &nbsp;niche&nbsp;overlap between subspecies was recorded (95%). Since there are very scarce&nbsp;<br />literature data about diet of the two subspecies, the data and results of this thesis are&nbsp;<br />particularly valuable.&nbsp;</p>

Amphibian diversity has declined, in part, due to the infectious disease chytridiomycosis, caused by the fungal pathogen Batrachochytrium dendrobatidis (Bd). Andean water frogs in the genus Telmatobius are particularly vulnerable to the disease and the genus has been extirpated from Ecuador and in Andean cloud forests, yet populations of species persist in the high Andes of Peru and Bolivia. The Alpaca Water Frog (Telmatobius intermedius), endemic to the Peruvian Andes, can be found infected with Bd. Alpaca Water Frogs inhabit high elevation open canopy freshwater systems. My overall goal was to study the effect of chytrid infection on the trophic ecology of Telmatobius tadpoles. I used stable isotope ratios of carbon (δ13C) and nitrogen (δ15N) to characterize the the trophic structure and energy flow in this system. I observed the values of δ15N were higher for tadpoles than algal material (t-test, t= -8.60, df= 34, p< 0.01), mayfly nymphs (t-test, t= 5.25, df= 30, p< 0.01), and predatory aquatic invertebrates (t-test, t= -4.18, df= 47, p< 0.01). In regard to the δ15N values of tadpoles and frogs, tadpoles had a lower value (t-test, t= -3.0, df= 31, p< 0.01). Values of δ15N in tadpoles were relatively high, signaling the presence of animal tissue in their diet. I also investigated changes in tadpole diet associated with mouthpart deformities caused by the fungal pathogen Bd. There was a positive association between the extent of mouthpart deformity and Bd infection (Fisher’s Exact test, p<0.001). The relative proportions of diatom morphotaxa groups found in the foregut of T. intermedius tadpoles varied in association with the degree of mouthpart deformity, as indicated by an ANOSIM analysis (R=0.875, p<0.001). Finally, in addition to Bd prevalence in adult aquatic frogs, I investigated whether Alpaca Water Frogs and other Andean Water Frogs tested positive for the antifungal bacterium Janthinobacterium lividum (Jliv). My results show that 57% of the sampled frogs were infected with Bd, 12.5% of frogs hosted both Jliv and Bd, while 7.2% hosted just Jliv. We found that the probability of an individual being infected with Bd was independent of the presence of Jliv; however, we did detect a protective effect of Jliv with respect to intensity of infection. My findings demonstrate that the fungal pathogen Bd influences the trophic ecology of tadpoles of Andean water frogs.

Drylands occupy about one-third of the world's land surface area and rivers in these regions have less predictable flow regimes than those in humid tropical and temperate regions. Australia's dryland river-floodplain systems cycle through recurrent periods of floods and droughts, oflen resulting in extreme hydrological variability. As a result, these systems have been described as having a 'boom and boost' ecology with periods of high productivity associated with flooding. Not surprisingly, flow and its variability have been recognised as major driving forces in the ecological functioning of Australian rivers and responses to flow variability from fish and aquatic invertebrates have been reasonably well described. Furthermore, the reduced amount of water reaching floodplain waterbodies due to river regulation has been held responsible for successional changes in aquatic biota and, consequently, the resources available for both fish and invertebrates. However, information regarding the impacts of water resource development has generally focused on within-channel processes of Australian rivers, not on floodplains, which are arguably more affected by water development. The following dissertation is concerned with how different types of natural and modified floodplain lagoons are able to trophically support their fish communities in the floodplain of the Macintyre River, Border Rivers catchment (QLD/NSW), a regulated dryland river. This study focuses on the influence of flooding and the implications of an extended dry period, and different levels of flow regulation, on the feeding ecology of selected fish species (Ambassis agassizil, Lelopotherapon unicolor and Nematalosa erebi) between 2001 and 2003. Food resources consumed by fish are hypothesised to vary in response to flooding, when inundation of isolated lagoons and vast floodplain areas can result in a burst of primary and secondary productivity. Given the permanently elevated water levels of some regulated floodplain lagoons, fish diets are hypothesised to be less variable in these floodplain habitats in comparison to diets of fish from floodplain lagoons with natural flow and water regime. Feeding ecology is examined firstly, in terms of diet composition of selected fish species, using stomach content analysis, and secondly, in relation to possible energy sources sustaining fish (using stable isotope analysis) in selected floodplain lagoons and a site in the main channel of the Macintyre River. The information produced should allow managers to take variations in food resources, food web structure and dietary ecology into account in management regimes for refugia and dryland systems in general. Factors such as diel and ontogenetic variations in dietary composition and food intake by fish are shown to considerably affect ovemll dietary patterns of each study species. Therefore, it is important to understand the contributions of such factors to the variability of fish dietary patterns before performing studies on resource use by fish in floodplain habitats of the Macintyre River. Major food categories consumed by the study species were zooplankton, aquatic invertebrates and detrital material. Zooplankton was of particular importance as this food item was ingested by all three study species at some stage of their life history. Spatial and temporal variation in diet composition of the study species was mostly associated with changes in prey items available across floodplain habitats and between seasons (summer/winter). The low magnitude of flooding events during the study period is arguably the most likely factor influencing the lack of patterns of variation in fish diets in floodplain habitats subject to flooding, whereas in non-flooded lagoons the observed dietary variation was a consequence of successional changes in composition of the aquatic fauna as the dry season progressed. Water regime had an important effect on differences in fish diet composition across lagoons, but further evaluation of the influence of flooding is needed due to overall lack of major flooding events during the study period. Autochthonous resources, namely plankton, were the basis of the food web and phytoplankton in the seston is the most likely ultimate energy source for fish consumers, via planktonic suspension feeders (zooplankton). Nevertheless, organic mailer could not be disregarded as an important energy source for invertebrates and higher consumers. In general, the present study does not provide support for the major models predicting the ftinctioning of large rivers, such as the River Continuum Concept and Flood Pulse Concept, which argue that allochthonous organic matter either from upstream or from the floodplain are the most important sources of carbon supporting higher consumers. In contrast, the Riverine Productivity Model would be more appropriate to describe the food web and energy sources for consumers in the Macintyre River floodplain as this model suggests that local productivity, based on autochthonous phytoplankton and organic matter, ftiels food webs in large rivers. The results of this study suggest that factors known to affect phytoplankton production in floodplain lagoons (e.g. flow regulation, turbidity and nutrient/herbicide inputs) must be seriously considered in current landscape and water management practices.

The greater Everglades ecosystem, including Florida Bay, has undergone significant anthropogenic manipulation over the past century. These actions resulted in a series of ecologically undesirable events in the Everglades ecosystem, prompting passage of the Comprehensive Everglades Restoration Plan (CERP). It is necessary to understand the variability in, and relationship between, salinity and ecology to fully evaluate the potential effects of CERP on Florida Bay. A seven-year dataset on surface salinity along with eleven-year and eight-year datasets on mesozooplankton and planktivorous fish were analyzed. Overall, mean Bay-wide salinity varied from a low of 24.2 just after the passing of Hurricane Irene in October 1999 to a high of 41.8 near the end of a drought period in July 2001. Bay-wide mean salinity exhibited dramatic decreases, up to 0.5 per day, whereas increases in bay-wide salinity were slower, with a maximum rate of 0.1 per day. Meteorological phenomena, such as tropical cyclones and ENSO, dramatically altered the salinity patterns of Florida Bay on interannual time scales. There was a large degree of spatial heterogeneity in salinity between sub-regions of Florida Bay due to differing freshwater sources and geomorphology. Mesozooplankton abundance displayed interannual variability and a positive correlation with salinity. Both of these features were also closely correlated with abundance of the dominant planktivorous fish, Anchoa mitchilli, indicating the importance of top-down control. The hypersaline periods appear to provide a refuge from predators, allowing mesozooplankton to increase in abundance during periods of increased physiological stress. The interaction between mesozooplankton and A. mitchilli, along with its correlation to salinity, was further investigated through the development of a mechanistic model of the populations in Florida Bay. The model indicated predation alone was insufficient to control mesozooplankton populations; rather, it was necessary to incorporate density-dependence utilizing a logistic prey population. With both mechanisms the model was able to replicate the observed interannual variability pattern and positive correlation between mesozooplankton and salinity. A preliminary management scenario evaluation suggests a two to six-fold difference in A. mitchilli and mesozooplankton populations between targeted and general salinity reductions. This suggests alternative freshwater management scenarios could produce drastically different ecological consequences.

A lake-wide benthic survey of Lake Erie during summer 2002 indicated that Dreissena bugensis is the dominant dreissenid in Lake Erie, especially in the east basin where this species was found at every station but no Dreissena polymorpha were collected. Mean (±SD) densities of dreissenid mussels were comparable between the west (601±2,110/m2,n=49) and central (635±1,293/m2; n=41) basins, but were much greater in the east basin (9,480±11,173/m2;n=17). The greater variability in mussel density among stations and replicate samples in the central and west basins than in the east basin is attributable to the preponderance of fine-grained substrata in the nearshore, higher episodic rates of sediment deposition and periodic hypoxia in bottom waters. Although there was little change in lake-wide mean dreissenid densities between 1992 and 2002 (declining from ca. 2,636 individuals/m2 to 2,025 individuals/m2), basin-averaged shell-free dry tissue mass increased by almost four-fold from ca. 6.8±15.6 g /m2 to 24.7±71.3 g/m2 in the same interval. Up to 90% of this biomass is in the eastern basin. Other changes in 2002 include the virtual absence of mussels in the 3 to 12 mm size range, probably because of predation by round gobies, and an increase in the average size of mature mussels. The substantial changes observed between 1992 and 2002 suggest that dreissenid populations in Lake Erie were still changing rapidly in abundance and biomass, as well as species composition. The results of this survey suggest that a direct link between Dreissena spp. and hypolimnetic hypoxia in the central basin is unlikely. The dominant organisms of Lake Erie in 2002 were D. rostriformis bugensis (38%), Oligochaeta (33%), Chironomidae (18%), Sphaeriidae (2.7%), Amphipoda (2.3%) and Hydrozoa (2.2%). Mean invertebrate density was greater in the east basin, especially on hard substrates, than either the west or central basin. In the central basin, sites ≥5m supported greater numbers of organisms, than shallow (≤2m) sites in the nearshore wave zone. The greatest number of taxa were observed in the central basin, likely a resutlt of greater sampling effort there. Gammarus fasciatus comprised 80% of all amphipods, being most abundant on Dreissena-dominated hard substrates in the east basin. The introduced species, Echinogammarus ischnus occured at only 11 of 69 sites, and was the only amphipod found at 4 east basin sites, but at relatively low densities. Diporeia were not found in our survey. Hexagenia was collected at only 4 stations, all in the west basin. Chironomids were dominated by Tanytarsus and Chironomus, with Procladius, Dicrotendipes and Polypedilum also being relatively common. Oligochaete Trophic Index for 2002 indicates a similarly mesotrophic condition throughout the lake and marginal nutrient enrichment of sediments between years 1979-2002. Multivariate ordination of community data indicates clear separation of sites by year and basin as expected given the extirpation of Diporeia and the introduction of Dreissena and E. ischnus, but also reveals subtle changes in benthic structure over the last 2 decades. The benthic community of Lake Erie in 2002 does not likely represent an equilibrium condition.

Total mercury (Hg) levels were determined in the tissues of ten taxa of pelagic fishes, with a special emphasis on apex predators (large vertebrates). Highest Hg levels were observed in blue marlin (Makaira nigricans), carcharhinid sharks (Genus Carcharhinus) and little tunny (Euthynnus alletteratus), ranging from 1.08 to 10.52 ppm. Moderate to low concentrations (<1.0 ppm) were observed in blackfin tuna (Thunnus atlanticus), cobia (Rachycentron canadum), dolphinfish (Coryphaena hippurus), greater amberjack (Seriola dumerili), king mackerel (Scomberomorus cavalla), wahoo (Acanthocybium solandri) and yellowfin tuna (Thunnus albacares). For the majority of species examined, Hg level did not vary significantly between locations (Texas and Louisiana) and years (2002 and 2003). The relationship between Hg level and fish size/weight was also explored and six taxa (blackfin tuna, carcharhinid sharks, dolphinfish, king mackerel, wahoo, yellowfin tuna) showed significant positive relationships between Hg level and body size and/or weight. Natural dietary tracers, stable isotopes (15N, 13C) and fatty acids were used to evaluate the relationship between Hg and trophic position and the relationship between Hg and dietary history. Stable nitrogen isotope analysis showed that Hg levels in fish tissues were positively associated with trophic position. Based on the 13C and 15N values of pelagic consumers examined in this study, three natural groups were identified with cluster analysis, and the same groupings were detected based on fatty acid profiles. This not only confirmed the existence of these natural groupings, but also indicated that the distinguishing factors for the grouping was likely connected with the dietary history of these fishes. The classification tree based on the fatty acid profiles of pelagic fishes readily separated fishes from different regions, suggesting that diets of pelagic taxa within the same region are similar or these consumers share a common source of organic matter in their food web. Findings from this study complement other Hg investigations conducted in the Gulf and also furthered our understanding of the link between feeding ecology and Hg accumulation. Moreover, the combined use of stable isotope and fatty acid techniques provided new insights on the dietary history of pelagic fishes in the Gulf of Mexico.

Trophic ecology is a key component in describing patterns of variation between and within populations, particularly in Arctic marine systems wherein climate change is impacting food webs. This thesis investigates the trophic ecology of Arctic char (Salvelinus alpinus) in the Cumberland Sound region using a multi-indicator approach. My data show trophic niche differences between resident and anadromous ecotypes and evidence for estuarine feeding by residents. I document a shift in the marine diet of Arctic char from zooplankton to capelin (Mallotus villosus) – a novel prey species in this region – that has occurred in less than a decade. Changes in Arctic char growth imply population-level effects of this shift; however, more research is required. Finally, I find lipid effects on δ13C and lipid-extraction effects on δ15N and δ34S for Arctic char muscle tissue. Lipid-correction models did not provide adequate δ13C estimates; thus, chemical extraction or ecotype-specific validation of models is recommended.

Trophic ecology is a key component in describing patterns of variation between and within populations, particularly in Arctic marine systems wherein climate change is impacting food webs. This thesis investigates the trophic ecology of Arctic char (Salvelinus alpinus) in the Cumberland Sound region using a multi-indicator approach. My data show trophic niche differences between resident and anadromous ecotypes and evidence for estuarine feeding by residents. I document a shift in the marine diet of Arctic char from zooplankton to capelin (Mallotus villosus) – a novel prey species in this region – that has occurred in less than a decade. Changes in Arctic char growth imply population-level effects of this shift; however, more research is required. Finally, I find lipid effects on δ13C and lipid-extraction effects on δ15N and δ34S for Arctic char muscle tissue. Lipid-correction models did not provide adequate δ13C estimates; thus, chemical extraction or ecotype-specific validation of models is recommended.