A comparative study of the pelagic food webs in two Newfoundland fjords using stable carbon and nitrogen isotope tracers

A comparative study was initiated to investigate the role of environmental variability on the trophic organization and structure of pelagic food chains in two fjords, Bay d'Espoir and Fortune Bay, along the south coast of Newfoundland, Canada. Although in close proximity, these fjords are biologically and physically distinct. On the basis of physical oceanographic studies, Bay d'Espoir was considered to be a relatively constant environment, while Fortune Bay had a dynamic water column, undergoing bi-annual deep-water renewal. Fauna, particulate organic matter (POM) and sediment were collected during summer and winter and analyzed for their stable carbon and nitrogen isotopic compositions. -- This study entailed the elucidation of the trophic organization of the most complex ecosystems yet analyzed using dual stable isotope tracers. Stable carbon and nitrogen isotopes used in combination provided better resolution than either could have given singly. However, they only allowed the assignment of species to a trophic level and did not in themselves provide information on the linkages between and within levels. -- The structure of the pelagic food webs and their principal food chains were determined for winter and summer. The trophic organization of the food webs was similar in both fjords within and between seasons; however, differences were observed in the food chains. With the exception of Bay d'Espoir in August, the top predators in both fjords occupied the fourth trophic level. The isotope data indicated which species were at intermediate trophic levels and the trophic position of the microzooplankton. -- Three pelagic food chains were present in Bay d'Espoir during both seasons, while Fortune Bay had three in the winter and two in summer. On the basis of the carbon and nitrogen isotopic composition of the fauna and POM it is suggested these pelagic food chains are affiliated with specific water types. This study is the first to draw attention to a relationship between the isotopic composition of the fauna and POM deeper than the subsurface layer. -- The trophic composition of the fauna differed between the two fjords; carnivores were dominant in Bay d'Espoir, while omnivores prevailed in Fortune Bay. A decrease in the proportion of omnivores in Fortune Bay was found between seasons, due to increased water column stability in the summer. -- A progressive enrichment of ¹³C and ¹⁵N in the fauna was found with increasing trophic level. Trophic level enrichments calculated for each food web varied slightly between fjords and seasons. These values corresponded closely to those reported in the literature and suggest similar mechanisms are involved in the fractionation of stable isotopes in food chains, independent of geographic location. Although minor differences were noted in the food chains, the overall trophic organization of the two fjords was similar to the Bering Sea (McConnaughey 1978) and the Scotian Shelf (Mills and Fournier 1979, Mills et al. 1984) ecosystems. This confirms the claims of Dickie (1972) and Mills (1975) that coastal ecosystems in general are similarly structured

Ammonium uptake and regeneration rates in a coastal upwelling regime

Ammonium uptake and regeneration rates were measured in time course experiments with 15N as a tracer. Both ammonium uptake and regeneration rates measured over 12 to 18 h remained essentially constant. However, as the length of the incubations increased the amount of usable data decreased dramatically due to substrate depletion and recycling of 15N. Mass balance calculations indicated that 22 to 51 % of the ammonium removed from the dissolved pool was not recovered in the particulate fraction. This appeared to be a more serious problem at 0 and 8 m (47%) than at 25 m (22%). As a result, ammonium uptake rates were probably underestimated. At 0, 12, and 20 m uptake rates either balanced or exceeded regeneration rates, while at 8 and 25 m net regeneration occurred. The fastest rates were measured during upwelling-induced phytoplankton blooms, intermediate rates characterized post-bloom conditions and the lowest rates coincided with an active upwelling event. Ammonium uptake rates were highest during the upwelling season (11 to 17 mmol N m-2 d-1) and lowest during the non-upwelling season (3 mmol N m-2 d-1), whereas regeneration rates did not differ significantly between seasons (11 to 20 mmol N m-2 d-1 ).Keywords: Ammonium uptake, Coastal upwelling, Ammonium regeneratio

Constraining bacterial production, conversion efficiency and respiration in the Ross

Abstract Bacteria consume dissolved organic carbon at rates averaging about 50% of primary production across a wide spectrum of marine ecosystems. However, total utilization rates are poorly constrained due to a lack of data on conversion eciencies and/or bacterial respiration rates. We estimated total community dark respiration rates (DCR) from in vitro oxygen utilization and estimated bacterial production from H-leucine incorporation during January}February 1997 in the Ross Sea, Antarctica. Bacterial respiration rates (BR) were estimated by assuming that BR was less than some fraction of DCR, and by choosing values for the bacterial growth eciency. By comparing these derived bacterial respiration rates with the DCR we were able to constrain conversion e$ciency and bacterial production within various bounds. Bacterial biomass was 10$ciencies had to be in the range of 35}45%, similar to independent discrete measurements made during the summer season on this cruise. Dark respiration rates are an absolute constraint on the estimates of bacterial carbon demand. A low value of the leucine conversion factor (1.5 kgC mol\) was required to meet this strong constraint

Effects of antiplatelet therapy on stroke risk by brain imaging features of intracerebral haemorrhage and cerebral small vessel diseases: subgroup analyses of the RESTART randomised, open-label trial

Background Findings from the RESTART trial suggest that starting antiplatelet therapy might reduce the risk of recurrent symptomatic intracerebral haemorrhage compared with avoiding antiplatelet therapy. Brain imaging features of intracerebral haemorrhage and cerebral small vessel diseases (such as cerebral microbleeds) are associated with greater risks of recurrent intracerebral haemorrhage. We did subgroup analyses of the RESTART trial to explore whether these brain imaging features modify the effects of antiplatelet therapy

A Multicenter Pilot Evaluation of the National Institutes of Health Chronic Graft-versus-Host Disease (cGVHD) Therapeutic Response Measures: Feasibility, Interrater Reliability, and Minimum Detectable Change

The lack of standardized criteria for measuring therapeutic response is a major obstacle to the development of new therapeutic agents for chronic graft-versus-host disease (cGVHD). National Institutes of Health (NIH) consensus criteria for evaluating therapeutic response were published in 2006. We report the results of four consecutive pilot trials evaluating the feasibility and estimating the inter-rater reliability and minimum detectable change of these response criteria

International genome-wide meta-analysis identifies new primary biliary cirrhosis risk loci and targetable pathogenic pathways.

Primary biliary cirrhosis (PBC) is a classical autoimmune liver disease for which effective immunomodulatory therapy is lacking. Here we perform meta-analyses of discovery data sets from genome-wide association studies of European subjects (n=2,764 cases and 10,475 controls) followed by validation genotyping in an independent cohort (n=3,716 cases and 4,261 controls). We discover and validate six previously unknown risk loci for PBC (Pcombined<5 × 10(-8)) and used pathway analysis to identify JAK-STAT/IL12/IL27 signalling and cytokine-cytokine pathways, for which relevant therapies exist

The International Bathymetric Chart of the Arctic Ocean Version 4.0

Funder: The Nippon Foundation of Japan, grant Seabed 2030Funder: Open access funding provided by Stockholm UniversityAbstract: Bathymetry (seafloor depth), is a critical parameter providing the geospatial context for a multitude of marine scientific studies. Since 1997, the International Bathymetric Chart of the Arctic Ocean (IBCAO) has been the authoritative source of bathymetry for the Arctic Ocean. IBCAO has merged its efforts with the Nippon Foundation-GEBCO-Seabed 2030 Project, with the goal of mapping all of the oceans by 2030. Here we present the latest version (IBCAO Ver. 4.0), with more than twice the resolution (200 × 200 m versus 500 × 500 m) and with individual depth soundings constraining three times more area of the Arctic Ocean (∼19.8% versus 6.7%), than the previous IBCAO Ver. 3.0 released in 2012. Modern multibeam bathymetry comprises ∼14.3% in Ver. 4.0 compared to ∼5.4% in Ver. 3.0. Thus, the new IBCAO Ver. 4.0 has substantially more seafloor morphological information that offers new insights into a range of submarine features and processes; for example, the improved portrayal of Greenland fjords better serves predictive modelling of the fate of the Greenland Ice Sheet