Gas hydrates occur at the sediment surface on the southern summit of Hydrate Ridge, Cascadia convergent margin. The hydrates are found in mounds several meters in diameter and up to 2 m high, and are covered by sediment and mats of the filamentous sulfur-oxidizing bacteria Beggiatoa. The mounds are surrounded by vesicomyid clams (Calyptogena pacifica, C. kilmeri), which in turn are encircled by solemyid bivalves (Acharax sp.). The zonation pattern of 3 species (Calyptogena spp. and Acharax sp., which harbor chemoautotrophic bacteria in their gills, and the chemoautotrophic Beggiatoa), is also reflected in a change in the entire community structure. Beggiatoa, Calyptogena spp. and Acharax sp. are shown to be characteristic species for the different communities. The Beggiatoa community directly overlaying the gas hydrates consists of seep endemic species in high densities: gastropods (Provanna laevis, P. lomana, Pyropelta corymba, Hyalogyrina sp. nov.), bivalves (Nuculana sp. nov.) and polychaetes (Ampharetidae, Polynoidae, Dorvilleidae). Based on pooled samples, the rarefaction curves show a decrease in species diversity in the Beggiatoa and Calyptogena communities. The hydrogen sulfide gradients in the porewater of sediments below the different communities dominated by either Beggiatoa, Calyptogena spp. or Acharax sp. vary by 3 orders of magnitude. The diffusive sulfide flux based on the measured sulfide concentration gradients is highest in Beggiatoa sp. communities (23 ± 13 mol m -2 yr -1 ), slightly less in Calyptogena communities (6.6 ± 2.4 mol m -2 yr -1 ), and low in Acharax communities (0.05 ± 0.05 mol m -2 yr -1). The difference in the sulfide environment is a factor influencing the distribution patterns of the chemoautotrophy-dependant and heterotrophic species at the deep-sea sediments containing gas hydrate.KEY WORDS: Gas hydrate · Community structure · Biomass · Diversity · Sulfide · Chemoautotrophy · Cold seep Resale or republication not permitted without written consent of the publisher

The North American Symptomatic Carotid Endarterectomy Trial (NASCET) has thus far demonstrated conclusive benefit for carotid endarterectomy for patients with symptomatic 70% to 99% internal carotid artery (ICA) stenosis. In the NASCET, ICA stenosis was classified angiographically: % ICA stenosis = (1-[narrowest ICA diameter/diameter normal distal cervical ICA]) x 100%. However, widely used duplex scan criteria for ICA stenosis correlate with different angiographic categories of high-grade stenosis (50% to 79%, > 80%) and were developed on the basis of estimated bulb diameter. We therefore blindly evaluated with separate observers carotid angiograms from 100 patients who also underwent carotid duplex scanning in our vascular laboratory. Methods: "Angiographic stenosis" was calculated as in NASCET. Duplex scan measurements of ICA peak systolic velocity (PSV), ICA end-diastolic velocity, and the ratio of ICA PSV to common carotid artery (CCA) PSV were analyzed for sensitivity, specificity, positive predictive value, negative predictive value, and overall accuracy to identify a 70% to 99% ICA stenosis. Results: Analysis of the data revealed that an ICA PSV/CCA PSV ratio of 4.0 provided the best combination of sensitivity (91%), specificity (87%), positive predictive value (76%), negative predictive value (96%), and overall accuracy (88%) for detection of a 70% to 99% stenosis. Conclusion: We conclude duplex scan determination of 70% to 99% stenosis as defined in the NASCET requires the adoption of duplex criteria modified from those in current use in most vascular laboratories.

Deep-sea hydrothermal vents are populated by dense communities of animals that form symbiotic associations with chemolithoautotrophic bacteria. To date, our understanding of which factors govern the distribution of host/symbiont associations (or holobionts) in nature is limited, although host physiology often is invoked. In general, the role that symbionts play in habitat utilization by vent holobionts has not been thoroughly addressed. Here we present evidence for symbiont-influenced, regional-scale niche partitioning among symbiotic gastropods (genus Alviniconcha) in the Lau Basin. We extensively surveyed Alviniconcha holobionts from four vent fields using quantitative molecular approaches, coupled to characterization of high-temperature and diffuse vent-fluid composition using gastight samplers and in situ electrochemical analyses, respectively. Phylogenetic analyses exposed cryptic host and symbiont diversity, revealing three distinct host types and three different symbiont phylotypes (one ε-proteobacteria and two γ-proteobacteria) that formed specific associations with one another. Strikingly, we observed that holobionts with ε-proteobacterial symbionts were dominant at the northern fields, whereas holobionts with γ-proteobacterial symbionts were dominant in the southern fields. This pattern of distribution corresponds to differences in the vent geochemistry that result from deep subsurface geological and geothermal processes. We posit that the symbionts, likely through differences in chemolithoautotrophic metabolism, influence niche utilization among these holobionts. The data presented here represent evidence linking symbiont type to habitat partitioning among the chemosynthetic symbioses at hydrothermal vents and illustrate the coupling between subsurface geothermal processes and niche availability. chemoautotrophy | symbiosis | endosymbiosis

Based on retrospective comparisons of duplex scanning with arteriography of the celiac (CA) and superior mesenteric (SMA) arteries in 34 patients, we previously suggested that an SMA peak systolic velocity of 275 cm/sec or greater or no flow signal and a CA PSV of 200 cm/sec or greater or no flow signal were reliable indicators of a 70% or greater angiographic stenosis of the SMA and CA, respectively. We now report the results of a blinded, prospective study in a larger patient group designed to determine the ability of mesenterie duplex scanning to visualize the CA and SMA and to validate our proposed duplex criteria for splanchnic artery stenosis. Methods: During an 18-month period 100 patients admitted to our vascular surgery service for aortography underwent routine mesenteric artery duplex scanning and lateral abdominal aortography regardless of abdominal symptoms. The lateral aortograms were evaluated to determine the presence or absence of a 70% or greater stenosis in the CA or SMA. Duplex-determined peak systolic velocities from the CA and SMA were recorded without knowledge of the angiographic results. Results: Aortography satisfactorily visualized 100% of the CAs and 99% of the SMAs. Of these, 93% of the SMAs and 83% of the CAs were visualized by duplex. According to the above criteria, duplex sensitivity, specificity, positive predictive value, negative predictive value, and overall accuracy for detection of a 70% or greater SMA stenosis were 92%, 96%, 80%, 99%, and 96% and for a 70% or greater CA stenosis 87%, 80%, 63%, 94%, and 82%. Conclusions: Mesenteric duplex scanning is feasible in the majority of patients. Prospective evaluation of duplex diagnostic criteria for 70% or greater stenosis indicates that mesenteric duplex scanning is sufficiently accurate to be clinically useful as a screening examination to detect SMA and CA stenosis.

Understanding why food chains are relatively short in length has been an area of research and debate for decades. We tested if progressive changes in the nutritional content of arthropods with trophic position limit the availability of a key nutrient, lipid, for carnivores. Arthropods at higher trophic levels had progressively less lipid and more protein in their bodies compared with arthropods at lower trophic levels. The nutrients present in arthropod bodies were directly related to the nutrients that predators extracted when feeding on those arthropods. As a consequence, nutrient assimilation shifted from lipid-biased to protein-biased as arthropods ascended trophic levels from herbivores to secondary carnivores. Successive changes in the nutritional consequences of predation may ultimately set an upper limit on the number of trophic levels in arthropod communities. Further work is needed to examine the influence of lipid and other nutrients on food web traits in a range of ecosystems.