Isotopic niche variability in macroconsumers of the East Scotia Ridge (Southern Ocean) hydrothermal vents: What more can we learn from an ellipse?

Aspects of between-individual trophic niche width can be explored through the isotopic niche concept. In many cases isotopic variability can be influenced by the scale of sampling and biological characteristics including body size or sex. Sample size-corrected (SEAc) and Bayesian (SEAb) standard ellipse areas and generalised least squares (GLS) models were used to explore the spatial variability of δ13C and δ15N in Kiwa tyleri (decapod), Gigantopelta chessoia (peltospirid gastropod) and Vulcanolepas scotiaensis (stalked barnacle) collected from 3 hydrothermal vent field sites (E2, E9N and E9S) on the East Scotia Ridge (ESR), Southern Ocean. SEAb only revealed spatial differences in isotopic niche area in male K. tyleri. However, the parameters used to draw the SEAc, eccentricity (E) and angle of the major SEAc axis to the x-axis (θ), indicated spatial differences in the relationships between δ13C and δ15N in all 3 species. The GLS models indicated that there were spatial differences in isotope-length trends, which were related to E and θ of the SEAc. This indicated that E and θ were potentially driven by underlying trophic and biological processes that varied with body size. Examination of the isotopic niches using standard ellipse areas and their parameters in conjunction with length-based analyses provided a means by which a proportion of the isotopic variability within each species could be described. We suggest that the parameters E and θ offer additional ecological insight that has so far been overlooked in isotopic niche studies

Drivers of intrapopulation variation in resource use in a generalist predator, the macaroni penguin

Intrapopulation variation in resource use occurs in many populations of generalist predators with important community and evolutionary implications. One of the hypothesised mechanisms for such widespread variation is ecological opportunity, i.e. resource availability determined by intrinsic constraints and extrinsic conditions. We combined tracking data and stable isotope analysis to examine how breeding constraints and prey conditions influenced intrapopulation variation in resource use among macaroni penguins Eudyptes chrysolophus. Isotopic variation was also examined as a function of breeding success, individual traits and individual specialisation. Variation in isotope ratios was greatest across multiple tissue types when birds were able to undertake mid-range foraging trips (i.e. during incubation and pre-moult). This variation was highly consistent between years that spanned a 3-fold difference in local krill Euphausia superba density and was also highly consistent at the individual level between 2 years that had similar krill densities. However, by comparing our results with previous work on the same population, it appeared that a decrease in local prey availability can increase intrapopulation variation in resource use during periods with more restricted foraging ranges (i.e. during brood-guard and crèche). This study highlights the importance of considering ecological interactions that operate on multiple spatio-temporal scales when examining the drivers of resource use in populations of generalist predators

Drivers of intrapopulation variation in resource use in a generalist predator, the macaroni penguin

Intrapopulation variation in resource use occurs in many populations of generalist predators with important community and evolutionary implications. One of the hypothesised mechanisms for such widespread variation is ecological opportunity, i.e. resource availability determined by intrinsic constraints and extrinsic conditions. In this study, we combined tracking data and stable isotope analysis to examine how breeding constraints and prey conditions influenced intrapopulation variation in resource use in a generalist predator, the macaroni penguin Eudyptes chrysolophus. Isotopic variation was also examined as a function of breeding success, individual traits and individual specialisation. Variation in isotope ratios was greatest across multiple tissue types when birds were able to undertake mid-range foraging trips (i.e. during incubation and pre-moult). This variation was highly consistent between years that spanned a 3-fold difference in local prey Euphausia superba density, and was also highly consistent at the individual level between 2 years that had similar prey densities. Furthermore, by comparing our results with previous work on the same population, it appeared that a decrease in local prey availability can also increase intrapopulation variation in resource use during periods with more restricted foraging ranges (i.e. during brood-guard and crèche). This study highlights the importance of considering ecological interactions that operate on multiple spatio-temporal scales when examining the drivers of resource use in populations of generalist predator

Migration strategies of skuas in the southwest Atlantic Ocean revealed by stable isotopes

Stable isotope ratios of carbon (δ13C) and nitrogen (δ15N) were measured in feathers to compare the non-breeding distributions and habitat use of adult brown skuas Stercorarius antarcticus lönnbergi from high-latitude colonies at Esperanza/Hope Bay (Antarctic Peninsula, 63°S) and Signy Island (South Orkneys, 60°S), with those from Bird Island (South Georgia, 54°S), which have also been tracked previously using geolocators. Breeding colony, but not sex, had a significant effect on feather δ13C and δ15N values. Feather stable isotope data from South Georgia birds mostly corresponded to oceanic, mixed subtropical–subantarctic to subantarctic waters, which agrees with the tracking data, as did a subset of the birds from the two higher latitude populations. However, other individuals displayed feather stable isotope ratios that were consistent with continental shelf or shelf-slope waters, suggesting that unlike the vast majority of brown skuas from South Georgia, many birds from higher latitude colonies spend the non-breeding season on, or near, the Patagonian Shelf. These population-level differences may have implications for exposure to anthropogenic threats or have carryover effects on subsequent breeding behaviour or performance

Diet and foraging areas of Southern Ocean seabirds and their prey inferred from stable isotopes: review and case study of Wilson's storm-petrel

Analysis of stable isotope ratios in animal tissues has emerged as a powerful tool for determining the trophic level and composition of prey and foraging location. We summarize here data on the stepwise trophic enrichment in d15N and latitudinal gradient in d13C in the Southern Ocean, and derive a regression equation to estimate latitudes from d13C values. We analysed isotope ratios of feathers of the small, pelagic seabird Wilson's storm-petrel <i>Oceanites oceanicus</i>, in different breeding stages, in comparison to isotope ratios of 4 other seabird species breeding in close vicinity on King George Island, South Shetland Islands. d15N analysis of feathers and albumen from Wilson's storm-petrels indicated a shift in diet from mainly crustaceans during egg formation to an increased proportion of fish during chick-feeding and moulting. d15N values of Wilson's storm-petrels during the chick-rearing season were closer to the mainly piscivorous-carnivorous skuas than to krill-feeding penguins, confirming that fish is an important part of their diet. d13C analysis of feathers identified 4 distinct foraging areas: d13C values in egg-white suggest that egg-forming females moved south to the sea ice edge. This coincides with the distribution of their main prey, Antarctic krill <i>Euphausia superba</i>, during this period

Re-constructing nutritional history of Serengeti wildebeest from stable isotopes in tail hair: seasonal starvation patterns in an obligate grazer

Rationale Nutritional bottlenecks often limit the abundance of animal populations and alter individual behaviours; however, establishing animal condition over extended periods of time using non-invasive techniques has been a major limitation in population ecology. We test if the sequential measurement of δ15N values in a continually growing tissue, such as hair, can be used as a natural bio-logger akin to tree rings or ice cores to provide insights into nutritional stress. Methods Nitrogen stable isotope ratios were measured by continuous-flow isotope-ratio mass spectrometry (IRMS) from 20 sequential segments along the tail hairs of 15 migratory wildebeest. Generalized Linear Models were used to test for variation between concurrent segments of hair from the same individual, and to compare the δ15N values of starved and non-starved animals. Correlations between δ15N values in the hair and periods of above-average energy demand during the annual cycle were tested using Generalized Additive Mixed Models. Results The time series of nitrogen isotope ratios in the tail hair are comparable between strands from the same individual. The most likely explanation for the pattern of 15N enrichment between individuals is determined by life phase, and especially the energetic demands associated with reproduction. The mean δ15N value of starved animals was greater than that of non-starved animals, suggesting that higher δ15N values correlate with periods of nutritional stress. Conclusions High δ15N values in the tail hair of wildebeest are correlated with periods of negative energy balance, suggesting they may be used as a reliable indicator of the animal's nutritional history. This technique might be applicable to other obligate grazers. Most importantly, the sequential isotopic analysis of hair offers a continuous record of the chronic condition of wildebeest (effectively converting point data into time series) and allows researchers to establish the animal's nutritional diary

The palaeoenvironment of East Kirkton, West Lothian, Scotland: stable isotope evidence from silicates and sulphides

Stable isotope data from the East Kirkton succession are used to elucidate the extent of hot-spring influence in the palaeoenvironment by constraining conditions of deposition of the silica and the formation of sulphides. Petrographically silica occurs as chert laminae thought to be primary, and as patchy chert considered as replacive. No evidence for biogenic silica was observed. For 20 silica samples δ18O was measured for structural oxygen and δD for bound water. δ18O(SMOW) varied between +21 and +27‰ with no sample groupings related to petrography. The range in δD(SMOW) was from −50 to −90‰ with lower values characterising replacive or altered silica; water contents of both petrographic groups were similar. A plot of δ18O versus δD for the laminated primary silica defines a grouping about the line defined by Scottish agates (Fallick et al. 1985). This suggests for the unaltered silica a formation temperature of about 60°C and a fluid containing a strong component of meteoric water. The data imply a Lower Carboniferous meteoric water δ18O composition of −3‰ and δD of −15‰, consistent with the known palaeolatitude. The only sulphide observed was pyrite; 34 samples were selected from a wide variety of lithological and textural occurrences. δ34S(CDT) ranges widely and continuously between +8 and −34‰ with no strong mode. The sulphur appears to be derived from several sources, and pyrite formation from a variety of conditions as indicated by such wide ranging data, but for the samples with the lowest δ34S the involvement of bacteria in sulphate reduction is inferred

Metal and selenium concentrations in blood and feathers of petrels of the genus Procellaria

Concentrations of copper (Cu), zinc (Zn), cadmium (Cd), lead (Pb), mercury (Hg), and selenium (Se) were determined in blood and feathers of spectacled (Procellaria conspicillata) and white-chinned (Procellaria aequinoctialis) petrels, species that are phylogenetically related, but with distinct ecological niches. In winter, they feed on similar foods, indicated by an overlapping range of whole-blood stable isotopes values (δ15N; δ13C). No relation was found between blood metal concentration and stable isotope values. In spectacled petrels, metal concentrations appeared lower in blood (Cu = 0.79–20.77 µg/g; Zn = 10.95–28.02 µg/g; Cd = 1.73–10.11 µg/g; Pb = 5.02–26.03 µg/g; Hg = 0.84–9.86 µg/g) than in feathers (Cu = 1.05–21.57 µg/g; Zn = 45.30–81.49 µg/g; Cd = 3.76–10.44 µg/g; Pb = 16.53–59.00 µg/g; Hg = 4.24–24.03 µg/g). In white-chinned petrels, metal concentrations also appeared lower in blood (Cu = 0.62–10.4 µg/g; Zn = 10.73–24.69 µg/g; Cd = 2.00–6.31 µg/g; Pb = 5.72–24.03 µg/g) than in feathers (Cu = 2.68–23.92 µg/g; Zn = 48.96–93.54 µg/g; Cd = 5.72–24.03 µg/g; Pb = 18.62–55.51 µg/g), except for Hg (blood = 0.20–15.82 µg/g; feathers = 0.19–8.91 µg/g). Selenium (0.24–14.18 µg/g) and Hg (0.22–1.44 µg/g) concentrations showed a positive correlation in growing feathers of spectacled petrels. Blood and feather Hg levels were higher in spectacled petrels while feathers Cu and Zn concentrations were greater in white-chinned petrels. Juvenile white-chinned petrels exhibited greater blood Hg concentrations than adults. In the south Atlantic Ocean, discards from commercial fishing operations consumed by spectacled petrels year-round and by white-chinned petrels during the wintering period have elevated Hg concentrations. Because Hg toxicity is associated with behavioral and reproductive changes in birds, it could potentially have impacts on breeding of these seabirds, as both species are listed as threatened by extinction. Environ Toxicol Chem 2013;32:1641–164

Biophysical and biochemical changes occur in Nephrops norvegicus during starvation

The nutritional status of an animal is maintained through a balance between energy intake and energy expenditure, and in the natural environment can fluctuate due to limited food availability and behavioural changes that remove the animal from its food. The integrated physiological processes that underlie an animal's nutritional status can be measured biophysically or biochemically. The Norway lobster Nephrops norvegicus has been shown to survive long periods of time without food, which is advantageous when food availability is low, such as during the winter months or when access to food is reduced due to risks associated with predation. In this study N. norvegicus was subjected to nutritional stress (starvation) for a period of 20 weeks and various biophysical measures (hepatosomatic index [HSI], length: weight ratio, tissue water content, carbon: nitrogen ratio) and biochemical measures (copper, carbohydrate, lipids, protein, stable isotopes δ15N δ13C) were used to determine how these animals maintain themselves over this period of forced starvation. Results indicate that while there was no variation in the whole weight of each individual, the organ-specific weight of the hepatopancreas (HSI) decreased and there was a corresponding increase in the water content of the hepatopancreas (and tail muscle). In contrast to the findings of previous studies, reserves of lipids decreased within the hepatopancreas. Fuel resources of protein from the tail muscle were not utilised, but reciprocal change in the copper content of the haemolymph to the hepatopancreas is suggestive of a breakdown of haemocyanin. The results provide an initial indication of how N. norvegicus can survive for long periods of time without food, and identify some potential biomarkers for starvation that can be applied to animals caught from the field