Pelagic squid associationswith a warm-core eddy of the East Australian Current

Cephalopods were sampled at night by midwater trawling in the upper 500 m in and near warm- core eddy F during summer. In all, 29 species (1019 specimens) were caught. Of the five dominant species, the squid Pterygioteuthis giardi and Brachioteuthis riisei were most numerous inside the eddy and Abraliopsis gilchristi and Pterygioteuthis gemmata had length-frequency distributions that were significantly larger outside than inside the eddy. A. gilchristi was also concentrated in warmer water and Pyroteuthis margaritifera was more common at 250 m than at shallower depths. Cluster analysis established a clear association of overall composition and relative abundances of cephalopod species with water temperature and location with respect to the eddy

Changes in Diet and Body Condition of Lake Whitefish in Southern Lake Michigan Associated with Changes in Benthos

We evaluated the long‐term trends of the benthic macroinvertebrate community (1980–1999) and biological attributes of lake whitefish Coregonus clupeaformis (1985–1999) in southeastern Lake Michigan. We also determined what food types were important to lake whitefish in an area where the amphipod Diporeia had not yet declined in 1998 and how the diet of lake whitefish changed as Diporeia declined during 1999–2000. Zebra mussels Dreissena polymorpha invaded the study area in 1992; Diporeia began to decline in 1993 and was nearly absent by 1999. The body condition of lake whitefish decreased after 1993 and remained low thereafter. The length at age and weight at age of lake whitefish was lower in 1992–1999 than in 1985–1991. After declines of Diporeia off the city of Muskegon, Michigan, between 1998 and 1999–2000, the proportion of Diporeia in the diet by weight fell from 70% to 25% and the percent occurrence decreased from 81% to 45%. In contrast, the proportion of lake whitefish that ate other prey, such as Mysis relicta (an opossum shrimp), ostracods, oligochaetes, and zooplankton, increased in the same period. At sites south of Muskegon, where the density of Diporeia has been low since 1998, chironomids, zebra mussels, and fingernail clams (Shaeriidae family) were the most important diet items of lake whitefish. Decreases in body condition and growth are associated with the loss of the high‐energy prey resource Diporeia, the consumption of prey with lower energy content, such as zebra mussels, and possible density‐dependence. Commercial harvests of lake whitefish will probably decrease because of low body condition and growth. Future management may require changes in harvest quotas, size restrictions, and depth restrictions as zebra mussel‐related impacts spread northward in Lake Michigan.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/142050/1/nafm0876.pd

Alewife planktivory controls the abundance of two invasive predatory cladocerans in Lake Michigan

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/74873/1/j.1365-2427.2007.01728.x.pd

Effects of Hypoxia on Consumption, Growth, and RNA:DNA Ratios of Young Yellow Perch

As in various freshwater and coastal marine ecosystems worldwide, seasonal bottom water hypoxia is a recurring phenomenon in Lake Erie’s central basin. While bottom hypoxia can strongly affect sessile benthic animals, its effects on mobile organisms such as fish are less understood. We evaluated the potential for bottom hypoxia to affect the growth rates of yellow perch Perca flavescens, a species of ecological and economic importance in the lake. To this end, we (1) conducted laboratory experiments to quantify the effects of reduced dissolved oxygen on consumption, somatic growth, and RNA : DNA ratios (an index of short‐term growth) of young yellow perch and (2) explored the effects of bottom hypoxia on young yellow perch growth in Lake Erie’s central basin by collecting individuals in hypoxicand normoxic regions of the lake and quantifying their RNA : DNA ratios. Yellow perch consumption and growth in our experiments declined under hypoxic conditions (≤2 mg O2/L). While yellow perch RNA : DNA ratios responded strongly to experimental temperature, nucleic acid ratios were not significantly affected by dissolved oxygen or feeding ration. We did, however, observe a positive correlation between yellow perch growth and RNA : DNA ratios at low temperatures (11°C). The nucleic acid ratios of yellow perch collected in Lake Erie varied spatiotemporally, but their patterns were not consistent with hypoxia. In short, while yellow perch consumption and growth rates respond directly and negatively to low oxygen conditions, these responses are not necessarily reflected in RNA : DNA ratios. Moreover, in central Lake Erie, where yellow perch can behaviorally avoid hypoxic areas, the RNA : DNA ratios of yellow perch do not respond strongly to bottom hypoxia. Thus, this study suggests that there is no strong negative effect of bottom hypoxia on the growth of young yellow perch in Lake Erie.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/141858/1/tafs1574.pd

Interactive Effects of Hypoxia and Temperature on Coastal Pelagic Zooplankton and Fish

Hypoxia, triggered in large part by eutrophication, exerts widespread and expanding stress on coastal ecosystems. Hypoxia is often specifically defined as water having dissolved oxygen (DO) concentrations < 2 mg L−1. However, DO concentration alone is insufficient to categorize hypoxic stress or predict impacts of hypoxia on zooplankton and fish. Hypoxic stress depends on the oxygen supply relative to metabolic demand. Water temperature controls both oxygen solubility and the metabolic demand of aquatic ectotherms. Accordingly, to assess impacts of hypoxia requires consideration of effects of temperature on both oxygen availability and animal metabolism. Temperature differences across ecosystems or across seasons or years within an ecosystem can dramatically impact the severity of hypoxia even at similar DO concentrations. Living under sub-optimum DO can reduce temperature-dependent metabolic efficiencies, prey capture efficiency, growth and reproductive potential, thus impacting production and individual zooplankton and fish fitness. Avoidance of hypoxic bottom water can reduce or eliminate low-temperature thermal refuges for organisms and increase energy demands and respiration rates, and potentially reduce overall fitness if alternative habitats are sub-optimal. Moreover, differential habitat shifts among species can shift predator-prey abundance ratios or interactions and thus modify food webs. For example, more tolerant zooplankton prey may use hypoxic waters as a refuge from fish predation. In contrast, zooplankton avoidance of hypoxic bottom waters can result in prey aggregations at oxyclines sought out by fish predators. Hypoxic conditions that affect spatial ecology can drive taxonomic and size shifts in the zooplankton community, affecting foraging, consumption and growth of fish. Advances in understanding the ecological effects of low DO waters on pelagic zooplankton and fish and comparisons among ecosystems will require development of generic models that estimate the oxygen demand of organisms in relation to oxygen supply which depends on both DO and temperature. We provide preliminary analysis of a metric (Oxygen Stress Level) which integrates oxygen demand in relation to oxygen availability for a coastal copepod and compare the prediction of oxygen stress to actual copepod distributions in areas with hypoxic bottom waters

Edge Tunneling of Vortices in Superconducting Thin Films

We investigate the phenomenon of the decay of a supercurrent due to the zero-temperature quantum tunneling of vortices from the edge in a thin superconducting film in the absence of an external magnetic field. An explicit formula is derived for the tunneling rate of vortices, which are subject to the Magnus force induced by the supercurrent, through the Coulomb-like potential barrier binding them to the film's edge. Our approach ensues from the non-relativistic version of a Schwinger-type calculation for the decay of the 2D vacuum previously employed for describing vortex-antivortex pair-nucleation in the bulk of the sample. In the dissipation-dominated limit, our explicit edge-tunneling formula yields numerical estimates which are compared with those obtained for bulk-nucleation to show that both mechanisms are possible for the decay of a supercurrent.Comment: REVTeX file, 15 pages, 1 Postscript figure; to appear in Phys.Rev.

Lake Erie hypoxia prompts Canada‐U.S. study

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95631/1/eost15589.pd

Exploring the spectral properties of faint hard X-ray sources with XMM-Newton

We present a spectroscopic study of 41 hard X-ray sources detected serendipitously with high significance (> 5 sigma in the 2-10 keV band) in seven EPIC performance/verification phase observations. The large collecting area of EPIC allows us to explore the spectral properties of these faint hard X-ray sources with 2< F_{2-10} < 80 x 10^{-14} erg cm^{-2}s^{-1} even though the length of the exposures are modest (~ 20 ks). Optical identifications are available for 21 sources of our sample. Using a simple power law plus Galactic absorption model we find an average value of the photon index Gamma ~ 1.6-1.7, broadly consistent with recent measurements made at similar fluxes with ASCA and with Chandra stacked spectral analyses. We find that 31 out of 41 sources are well fitted by this simple model and only eight sources require absorption in excess of the Galactic value. Interestingly enough, one third of these absorbed sources are broad line objects, though with moderate column densities. Two sources in the sample are X-ray bright optically quiet galaxies and show flat X-ray spectra. Comparing our observational results with those expected from standard synthesis models of the cosmic X-ray background (CXB) we find a fraction of unabsorbed to absorbed sources larger than predicted by theoretical models at our completeness limit of F_{2-10} ~ 5 x 10^{-14} erg cm^{-2}s^{-1}. The results presented here illustrate well how wide-angle surveys performed with EPIC on board XMM-Newton allow population studies of interesting and unusual sources to be made as well as enabling constraints to be placed on some input parameters for synthesis models of the CXB.Comment: 16 pages, 11 figures. To be published in A&

Exercise, APOE, and Working Memory: MEG and Behavioral Evidence for Benefit of Exercise in Epsilon4 Carriers

Performance on the Sternberg working memory task, and MEG cortical response on a variation of the Sternberg task were examined in middle-aged carriers and non-carriers of the APOE ε4 allele. Physical activity was also assessed to examine whether exercise level modifies the relationship between APOE genotype and neurocognitive function. Regression revealed that high physical activity was associated with faster RT in the six- and eight-letter conditions of the Sternberg in ε4 carriers, but not in the non-carriers after controlling for age, gender, and education (N = 54). Furthermore, the MEG analysis revealed that sedentary ε4 carriers exhibited lower right temporal lobe activation on matching probe trials relative to high-active ε4 carriers, while physical activity did not distinguish non-carriers (N = 23). The M170 peak was identified as a potential marker for pre-clinical decline as ε4 carriers exhibited longer M170 latency, and highly physically active participants exhibited greater M170 amplitude to matching probe trials