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| 2. |
- Attard, Karl M., et al.
(författare)
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Benthic oxygen exchange in a live coralline algal bed and an adjacent sandy habitat : an eddy covariance study
- 2015
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Ingår i: Marine Ecology Progress Series. - : Inter-Research. - 0171-8630 .- 1616-1599. ; 535, s. 99-115
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Tidskriftsartikel (refereegranskat)abstract
- Coralline algal (maerl) beds are widespread, slow-growing, structurally complex perennial habitats that support high biodiversity, yet are significantly understudied compared to seagrass beds or kelp forests. We present the first eddy covariance (EC) study on a live maerl bed, assessing the community benthic gross primary productivity (GPP), respiration (R), and net ecosystem metabolism (NEM) derived from diel EC time series collected during 5 seasonal measurement campaigns in temperate Loch Sween, Scotland. Measurements were also carried out at an adjacent (similar to 20 m distant) permeable sandy habitat. The O-2 exchange rate was highly dynamic, driven by light availability and the ambient tidally-driven flow velocity. Linear relationships between the EC O-2 fluxes and available light indicate that the benthic phototrophic communities were light limited. Compensation irradiance (E-c) varied seasonally and was typically similar to 1.8-fold lower at the maerl bed compared to the sand. Substantial GPP was evident at both sites; however, the maerl bed and the sand habitat were net heterotrophic during each sampling campaign. Additional inputs of similar to 4 and similar to 7 mol m(-2) yr(-1) of carbon at the maerl bed and sand site, respectively, were required to sustain the benthic O-2 demand. Thus, the 2 benthic habitats efficiently entrap organic carbon and are sinks of organic material in the coastal zone. Parallel deployment of 0.1 m(2) benthic chambers during nighttime revealed O-2 uptake rates that varied by up to similar to 8-fold between replicate chambers (from -0.4 to -3.0 mmol O-2 m(-2) h(-1); n = 4). However, despite extensive O-2 flux variability on meter horizontal scales, mean rates of O-2 uptake as resolved in parallel by chambers and EC were typically within 20% of one another.
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| 3. |
- Attard, Karl M., et al.
(författare)
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Metabolism of a subtidal rocky mussel reef in a high-temperate setting : pathways of organic C flow
- 2020
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Ingår i: Marine Ecology Progress Series. - : Inter-Research Science Center. - 0171-8630 .- 1616-1599. ; 645, s. 41-54
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Tidskriftsartikel (refereegranskat)abstract
- Mytilid mussels form abundant, species-rich reefs on rocky substrates, but the role of this key habitat in carbon (C) cycling remains poorly understood. We performed a seasonal study on a 5 m deep photic Mytilus trossulus reef in the Central Baltic Sea to investigate pathways and rates of organic C flow. Reef gross primary production (GPP) and respiration (R) were estimated seasonally using underwater O2 eddy covariance on hourly and daily timescales. Photogrammetry and biotic sampling were used to quantify reef rugosity and mussel coverage, and to derive mussel filtration and biodeposition. Mussels were highly abundant, reaching ~50000 ind. m-2, and the reef structure increased the seabed surface area by 44%. GPPhourly was up to 20 mmol O2 m-2 h-1 and GPPdaily was up to 107 mmol O2 m-2 d-1, comparable to a nearby seagrass canopy. Hourly eddy fluxes responded linearly to light intensity and flow velocity, with higher velocities enhancing reef O2 uptake at night. Reef Rdaily exceeded GPPdaily on 12 of 13 measurement days, and Rannual (29 mol O2 m-2 yr-1) was 3-fold larger than GPPannual. The reef sustained a productive community of microbes and fauna whose activities accounted for ~50% of Rannual. Horizontal water advection promoted food supply to the reef and likely facilitated substantial lateral C export of mussel biodeposits. Our analyses suggest that a reduction in mussel reef extent due to ongoing environmental change will have major implications for the transport and transformation of C and nutrients within the coastal Baltic Sea.
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| 4. |
- Attard, Karl M., et al.
(författare)
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Seasonal ecosystem metabolism across shallow benthic habitats measured by aquatic eddy covariance
- 2019
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Ingår i: Limnology and Oceanography Letters. - : Wiley. - 2378-2242. ; 4:3, s. 79-86
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Tidskriftsartikel (refereegranskat)abstract
- Shallow benthic habitats are hotspots for carbon cycling and energy flow, but metabolism (primary production and respiration) dynamics and habitat-specific differences remain poorly understood. We investigated daily, seasonal, and annual metabolism in six key benthic habitats in the Baltic Sea using similar to 2900h of in situ aquatic eddy covariance oxygen flux measurements. Rocky substrates had the highest metabolism rates. Habitat-specific annual primary production per m(2) was in the order Fucus vesiculosus canopy>Mytilus trossulus reef>Zostera marina canopy>mixed macrophytes canopy>sands, whereas respiration was in the order M. trossulus>F. vesiculosus>Z. marina>mixed macrophytes> sands>aphotic sediments. Winter metabolism contributed 22-31% of annual rates. Spatial upscaling revealed that benthic habitats drive >90% of ecosystem metabolism in waters <= 5 m depth, highlighting their central role in carbon and nutrient cycling in shallow waters.
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| 5. |
- Balmonte, John Paul, et al.
(författare)
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Sharp contrasts between freshwater and marine microbial enzymatic capabilities, community composition, and DOM pools in a NE Greenland fjord
- 2020
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Ingår i: Limnology and Oceanography. - : WILEY. - 0024-3590 .- 1939-5590. ; 65:1, s. 77-95
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Tidskriftsartikel (refereegranskat)abstract
- Increasing glacial discharge can lower salinity and alter organic matter (OM) supply in fjords, but assessing the biogeochemical effects of enhanced freshwater fluxes requires understanding of microbial interactions with OM across salinity gradients. Here, we examined microbial enzymatic capabilities-in bulk waters (nonsize-fractionated) and on particles (>= 1.6 mu m)-to hydrolyze common OM constituents (peptides, glucose, polysaccharides) along a freshwater-marine continuum within Tyrolerfjord-Young Sound. Bulk peptidase activities were up to 15-fold higher in the fjord than in glacial rivers, whereas bulk glucosidase activities in rivers were twofold greater, despite fourfold lower cell counts. Particle-associated glucosidase activities showed similar trends by salinity, but particle-associated peptidase activities were up to fivefold higher-or, for several peptidases, only detectable-in the fjord. Bulk polysaccharide hydrolase activities also exhibited freshwater-marine contrasts: xylan hydrolysis rates were fivefold higher in rivers, while chondroitin hydrolysis rates were 30-fold greater in the fjord. Contrasting enzymatic patterns paralleled variations in bacterial community structure, with most robust compositional shifts in river-to-fjord transitions, signifying a taxonomic and genetic basis for functional differences in freshwater and marine waters. However, distinct dissolved organic matter (DOM) pools across the salinity gradient, as well as a positive relationship between several enzymatic activities and DOM compounds, indicate that DOM supply exerts a more proximate control on microbial activities. Thus, differing microbial enzymatic capabilities, community structure, and DOM composition-interwoven with salinity and water mass origins-suggest that increased meltwater may alter OM retention and processing in fjords, changing the pool of OM supplied to coastal Arctic microbial communities.
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| 6. |
- Bonaglia, Stefano, et al.
(författare)
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Meiofauna improve oxygenation and accelerate sulfide removal in the seasonally hypoxic seabed
- 2020
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Ingår i: Marine Environmental Research. - : Elsevier BV. - 0141-1136 .- 1879-0291. ; 159
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Tidskriftsartikel (refereegranskat)abstract
- Oxygen depleted areas are widespread in the marine realm. Unlike macrofauna, meiofauna are abundant in hypoxic sediments. We studied to what extent meiofauna affect oxygen availability, sulfide removal and microbial communities. Meiofauna were extracted alive and added to intact sediments simulating abundance gradients previously reported in the area. A total of 324 porewater microprofiles were recorded over a 3-week incubation period and microbial community structure and cable bacteria densities were determined at the end of the experiment. At high abundances meiofauna activity deepened oxygen penetration by 85%, 59%, and 62% after 5, 14, and 22 days, respectively, compared to control sediment with scarce meiofauna. After 6 days, meiofauna increased the volume of oxidized, sulfide-free sediment by 68% and reduced sulfide fluxes from 8.8 to 0.4 mmol m(-2) d(-1). After 15 days, the difference with the control attenuated due to the presence of a cable bacteria population, which facilitated sulfides oxidation in all treatments. 16S rRNA gene analysis revealed that meiofauna affected microbial community structure (beta diversity). Thus, meiofauna bioturbation plays an important role in deepening oxygen penetration, counteracting euxinia and in structuring microbial diversity of hypoxic sediments. Co-existence with cable bacteria demonstrates neutralism interaction between these two ecosystem engineers.
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| 7. |
- Carroll, Christopher, et al.
(författare)
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Hypoxia Generated by Avian Embryo Growth Induces the HIF-α Response and Critical Vascularization
- 2021
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Ingår i: Frontiers in Ecology and Evolution. - : Frontiers Media SA. - 2296-701X. ; 9, s. 1-15
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Tidskriftsartikel (refereegranskat)abstract
- Cancer research has transformed our view on cellular mechanisms for oxygen sensing. It has been documented that these mechanisms are important for maintaining animal tissues and life in environments where oxygen (O2) concentrations fluctuate. In adult animals, oxygen sensing is governed by the Hypoxia Inducible Factors (HIFs) that are stabilized at low oxygen concentrations (hypoxia). However, the importance of hypoxia itself during development and for the onset of HIF-driven oxygen sensing remains poorly explored. Cellular responses to hypoxia associates with cell immaturity (stemness) and proper tissue and organ development. During mammalian development, the initial uterine environment is hypoxic. The oxygenation status during avian embryogenesis is more complex since O2 continuously equilibrates across the porous eggshell. Here, we investigate HIF dynamics and use microelectrodes to determine O2 concentrations within the egg and the embryo during the first four days of development. To determine the increased O2 consumption rates, we also obtain the O2 transport coefficient (DO2) of eggshell and associated inner and outer shell membranes, both directly (using microelectrodes in ovo for the first time) and indirectly (using water evaporation at 37.5°C for the first time). Our results demonstrate a distinct hypoxic phase (<5% O2) between day 1 and 2, concurring with the onset of HIF-α expression. This phase of hypoxia is demonstrably necessary for proper vascularization and survival. Our indirectly determined DO2 values are about 30% higher than those determined directly. A comparison with previously reported values indicates that this discrepancy may be real, reflecting that water vapor and O2 may be transported through the eggshell at different rates. Based on our obtained DO2 values, we demonstrate that increased O2 consumption of the growing embryo appears to generate the phase of hypoxia, which is also facilitated by the initially small gas cell and low membrane permeability. We infer that the phase of in ovo hypoxia facilitates correct avian development. These results support the view that hypoxic conditions, in which the animal clade evolved, remain functionally important during animal development. The study highlights that insights from the cancer field pertaining to the cellular capacities by which both somatic and cancer cells register and respond to fluctuations in O2 concentrations can broadly inform our exploration of animal development and success.
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| 8. |
- Cheung, Henry Lok Shan, et al.
(författare)
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Denitrification, anammox, and DNRA in oligotrophic continental shelf sediments
- 2024
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Ingår i: Limnology and Oceanography. - 1939-5590 .- 0024-3590.
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Tidskriftsartikel (refereegranskat)abstract
- Continental shelf sediments are considered hotspots for nitrogen (N) removal. While most investigations have quantified denitrification in shelves receiving large amounts of anthropogenic nutrient supply, we lack insight into the key drivers of N removal on oligotrophic shelves. Here, we measured rates of N removal through denitrification and anammox by the revised-isotope pairing technique (r-IPT) along the Northeastern New Zealand shelf. Denitrification dominated total N2 production at depths between 30 and 128 m with average rates (± SE) ranging from 65 ± 28 to 284 ± 72 μmol N m−2 d−1. N2 production by anammox ranged from 3 ± 1 to 28 ± 11 μmol N m−2 d−1 and accounted for 2–19% of total N2 production. DNRA was negligible in these oligotrophic settings. Parallel microbial community analysis showed that both Proteobacteria and Planctomycetota were key taxa driving denitrification. Denitrification displayed a negative correlation with oxygen penetration depth, and a positive correlation with macrofauna abundance. Our denitrification rates were comparable to oligotrophic shelves from the Arctic, but were lower than those from nutrient-rich Pacific and Atlantic shelves. Based on our results and existing IPT measurements, the global shelf denitrification rate was reassessed to be 53.5 ± 8.1 Tg N yr−1, equivalent to 20 ± 2% of marine N removal. We suggest that previous estimates of global shelf N loss might have been overestimated due to sampling bias toward areas with high N loads in the Northern Hemisphere.
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| 9. |
- Maciute, Adele, et al.
(författare)
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A microsensor-based method for measuring respiration of individual nematodes
- 2021
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Ingår i: Methods in Ecology and Evolution. - 2041-210X. ; 12:10, s. 1841-1847
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Tidskriftsartikel (refereegranskat)abstract
- Meiofauna (invertebrates that pass through a 1-mm mesh sieve, but are retained on a 40-µm mesh) represent the most abundant and diverse animal group on Earth, but empirical evidence of their role in benthic respiration, production and carbon cycling across ecosystems is not well documented. Moreover, how meiofauna respond to changing oxygen conditions is poorly understood. We further developed an incubation system, in which oxygen and temperature conditions are easily controlled and single meiofaunal nematode respiration is resolved in glass capillary tubes, using Clark-type oxygen microsensor. We performed the respiration measurements after exposing nematodes to different ambient oxygen concentrations, which resulted in 3–60µM O2 during hypoxic and 80–210µM O2 during oxic incubations in close proximity to the respective nematodes. Individual nematode respiration rates ranged from 0.02 to 1.30nmol O2 ind.−1day−1 and were 27% lower during hypoxic than oxic incubations. Rates derived from established allometric relations were on average fourfold higher than our direct measurements. The presented method is suitable for single nematode respiration measurements and can be adapted to a wide range of experimental conditions. Therefore, it can be used to assess meiofauna contribution to ecosystem processes and investigate species-specific responses to changing environmental conditions, for example, oxygen stress, increasing water temperature.
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