Resource partitioning between Pacific walruses and bearded seals in the Alaska Arctic and sub-Arctic.

Climate-mediated changes in the phenology of Arctic sea ice and primary production may alter benthic food webs that sustain populations of Pacific walruses (Odobenus rosmarus divergens) and bearded seals (Erignathus barbatus). Interspecific resource competition could place an additional strain on ice-associated marine mammals already facing loss of sea ice habitat. Using fatty acid (FA) profiles, FA trophic markers, and FA stable carbon isotope analyses, we found that walruses and bearded seals partitioned food resources in 2009-2011. Interspecific differences in FA profiles were largely driven by variation in non-methylene FAs, which are markers of benthic invertebrate prey taxa, indicating varying consumption of specific benthic prey. We used Bayesian multi-source FA stable isotope mixing models to estimate the proportional contributions of particulate organic matter (POM) from sympagic (ice algal), pelagic, and benthic sources to these apex predators. Proportional contributions of FAs to walruses and bearded seals from benthic POM sources were high [44 (17-67)% and 62 (38-83)%, respectively] relative to other sources of POM. Walruses also obtained considerable contributions of FAs from pelagic POM sources [51 (32-73)%]. Comparison of δ13C values of algal FAs from walruses and bearded seals to those from benthic prey from different feeding groups from the Chukchi and Bering seas revealed that different trophic pathways sustained walruses and bearded seals. Our findings suggest that (1) resource partitioning may mitigate interspecific competition, and (2) climate change impacts on Arctic food webs may elicit species-specific responses in these high trophic level consumers.

Antimicrobial activity of cyclodextrin entrapped allyl isothiocyanate in a model system and packaged fresh-cut onions.

The aim of this work was to determine the antimicrobial effect of allyl isothiocyanate (AIT) entrapped in alpha and beta cyclodextrin inclusion complexes (ICs). In model experiments, AIT formulations were applied to filter paper discs fixed inside the lid of Petri dishes, where the agar surface was inoculated with the target organism (Penicillium expansum, Escherichia coli or Listeria monocytogenes). Solid phase microextraction coupled with gas chromatography was used to determine static headspace concentrations of AIT formulations. The antimicrobial effect of beta IC was determined during aerobic storage of packaged fresh-cut onions at 5 °C for 20 days. AIT entrapped in beta IC exhibited a significantly (p < 0.05) better antimicrobial effect compared to unentrapped AIT. AIT vapour concentrations in the static system were highest for unentrapped AIT followed by beta IC and alpha IC. Application of beta IC (200 µl/l) to packaged fresh-cut onions effectively decreased numbers of L. monocytogenes, which were also decreased at slower rates to undetectable levels on untreated cut onion. After 10 days, total aerobic counts were ca. 4 log CFU/g lower on onions treated with beta IC (100 and 200 µl/l) compared to untreated controls. This work demonstrates the utility of beta IC as an antimicrobial treatment with potential applications in packaged fresh-cut vegetable products.

Rapid method for determination of residual tert-butanol in liposomes using solid-phase microextraction and gas chromatography.

A simple, rapid, and reliable method to detect residual levels of tert-butanol in liposomes using sec-butanol as an internal standard has been developed. Solid-phase microextraction (SPME) followed by gas chromatographic analysis was used to quantify the amount of residual tert-butanol in freeze-dried liposome material. Only 1 min was necessary for reproducible amounts of analyte to absorb onto the SPME fiber, and because this method requires very little sample preparation, a single analysis can be completed in less than 15 min. This method had a linear range of 10-600 microg/mL. Careful control of times of temperature equilibration and exposure to headspace was necessary to ensure reproducible results. This method can easily be applied to other applications in the food and pharmaceutical industries where detection of residual solvents, such as hexane and chloroform, is necessary.

Tracing carbon flow in an arctic marine food web using fatty acid-stable isotope analysis.

Global warming and the loss of sea ice threaten to alter patterns of productivity in arctic marine ecosystems because of a likely decline in primary productivity by sea ice algae. Estimates of the contribution of ice algae to total primary production range widely, from just 3 to >50%, and the importance of ice algae to higher trophic levels remains unknown. To help answer this question, we investigated a novel approach to food web studies by combining the two established methods of stable isotope analysis and fatty acid (FA) analysis--we determined the C isotopic composition of individual diatom FA and traced these biomarkers in consumers. Samples were collected near Barrow, Alaska and included ice algae, pelagic phytoplankton, zooplankton, fish, seabirds, pinnipeds and cetaceans. Ice algae and pelagic phytoplankton had distinctive overall FA signatures and clear differences in delta(13)C for two specific diatom FA biomarkers: 16:4n-1 (-24.0+/-2.4 and -30.7+/-0.8 per thousand, respectively) and 20:5n-3 (-18.3+/-2.0 and -26.9+/-0.7 per thousand, respectively). Nearly all delta(13)C values of these two FA in consumers fell between the two stable isotopic end members. A mass balance equation indicated that FA material derived from ice algae, compared to pelagic diatoms, averaged 71% (44-107%) in consumers based on delta(13)C values of 16:4n-1, but only 24% (0-61%) based on 20:5n-3. Our estimates derived from 16:4n-1, which is produced only by diatoms, probably best represented the contribution of ice algae relative to pelagic diatoms. However, many types of algae produce 20:5n-3, so the lower value derived from it likely represented a more realistic estimate of the proportion of ice algae material relative to all other types of phytoplankton. These preliminary results demonstrate the potential value of compound-specific isotope analysis of marine lipids to trace C flow through marine food webs and provide a foundation for future work.