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  • 1
    Electronic Resource
    Electronic Resource
    In vivo measurements of the internal pH of Hediste (Nereis) diversicolor (Annelida, Polychaeta) exposed to ambient sulphidic conditions using pH microelectrodes (2000)
    Springer
    Naturwissenschaften 87 (2000), S. 283-287 
    Details
    ISSN: 1432-1904
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Natural Sciences in General
    Notes: Abstract  The effect of different ambient sulphide concentrations on the internal pH regime of Hediste (Nereis) diversicolor was studied under in vivo conditions using liquid membrane pH microelectrodes, a method which is new to marine sciences. As a case study, the hypothesis was tested whether organisms exposed to ambient sulphidic conditions are able to lower their internal pH which, in effect, would reduce sulphide influx into the animals and thus could represent an effective detoxification mechanism. It was shown that a significant lowering of the internal pH occurred within only 20 min after adding sulphide. This pH lowering appeared to be dependent on the external sulphide concentration of the ambient medium and showed a saturation beyond a threshold level of about 130 μM. It is discussed whether this sulphide-induced pH drop is an active regulatory mechanism and acts as an effective protection mechanism against sulphide during short-term exposures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s001140050723
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    Paper (German National Licenses)
    Fulltext
  • 2
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    The squat lobster Pleuroncodes monodon tolerates anoxic "dead zone" conditions off Peru (2015)
    Springer
    In:  Marine Biology, 162 (9). pp. 1913-1921.
    Details
    Publication Date: 2019-09-23
    Description: The squat lobster Pleuroncodes monodon is a key species of the highly productive, but oxygen-poor upwelling system of the Eastern Tropical South Pacific. Observations of P. monodon in the water column off Peru have led to the hypothesis that anoxic conditions force this otherwise primarily benthic species to adopt a pelagic lifestyle. Here we show that off Peru, P. monodon can be found in the oxygenated surface water, but also on the anoxic seafloor. Our physiological experiments demonstrate that juvenile and adult specimens have a very low critical respiratory pO2 of 0.5 kPa and that adults survive anoxia for 30.5–70.5 h. Anoxic conditions at the seafloor should therefore force P. monodon to regularly migrate to the oxic surface layer in order to restore energy reserves and recycle metabolic end products of anaerobic metabolism. It was recently estimated that the ammonium supply mediated by diel vertical migrations (DVMs) of zooplankton and nekton considerably fuels bacterial anaerobic ammonium oxidation—a major loss process for fixed nitrogen in the ocean. These estimates were based on the implicit assumption that anoxia does not result in a down-regulation of ammonium excretion. We here show that exposure to anoxia elicits a fourfold reduction in ammonium excretion from 2.1 ± 0.6 µmol h−1 g dry weight−1 under normoxic to 0.5 ± 0.6 µmol h−1 g DW−1 under anoxic conditions in P. monodon. Estimates of ammonium supply to the anoxic core of oxygen minimum zones via DVM therefore are likely too high.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1007/s00227-015-2709-6
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 3
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    Simple, robust eddy correlation amplifier for aquatic dissolved oxygen and hydrogen sulfide flux measurements (2011)
    American Society of Limnology and Oceanography
    In:  Limnology and Oceanography: Methods, 9 . pp. 340-347.
    Details
    Publication Date: 2018-08-15
    Description: The aquatic application of the eddy correlation (EC) technique is growing more popular and is gradually becoming a standard method for resolving benthic O2 fluxes. By including the effects of the local hydrodynamics, the EC technique provides greater insight into the nature of benthic O2 exchange than traditional methods (i.e., benthic chambers and lander microprofilers). The growing popularity of the EC technique has led to a greater demand for easily accessible and robust EC instrumentation. Currently, the EC instrumentation is limited to two commercially available systems that are still in the development stage. Here, we present a robust, open source EC picoamplifier that is simple in design and can be easily adapted to both new and existing acoustic Doppler velocimeters (ADV). The picoamplifier has a response time of 〈 0.1 ms and features galvanic isolation that ensures very low noise contamination of the signal. It can be adjusted to accommodate varying ranges of microelectrode sensitivity as well as other types of amperometric microelectrodes. We show that the extracted flux values are not sensitive to reduced microelectrode operational ranges (i.e., lower resolution) and that no signal loss results from using either a 16- or 14-bit analog-to-digital converter. Finally, we demonstrate the capabilities of the picoamplifier with field studies measuring both dissolved O2 and H2S EC fluxes. The picoamplifier presented here consistently acquires high-quality EC data and provides a simple solution for those who wish to obtain EC instrumentation. The schematic of the amplifier’s circuitry is given in the Web Appendix.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
    Format: text
    DOI: 10.4319/lom.2011.9.340
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 4
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    Evaluation of a lifetime-based optode to measure oxygen in aquatic systems (2006)
    American Society of Limnology and Oceanography
    In:  Limnology and Oceanography: Methods, 4 . pp. 7-17.
    Details
    Publication Date: 2019-09-23
    Description: In this article, we evaluate the performance of a commercially available lifetime-based optode and compare it with data obtained by other methods. We performed a set of 10 different tests, including targeted laboratory evaluations and field studies, covering a wide range of situations from shallow coastal waters and wastewater treatment plants to abyssal depths. Our principal conclusion is that, owing to high accuracy (± 2 µM), long-term stability (more than 20 months), lack of pressure hysteresis, and limited cross-sensitivity, this method is overall more suitable for oxygen monitoring than other methods.
    Type: Article , PeerReviewed
    Format: text
    Format: text
    DOI: 10.4319/lom.2006.4.7
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 5
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    Gas exchange system for extended in situ benthic chamber flux measurements under controlled oxygen conditions: First application - Sea bed methane emission measurements at Captain Arutyunov mud volcano (2008)
    American Society of Limnology and Oceanography
    In:  Limnology and Oceanography: Methods, 6 . pp. 23-33.
    Details
    Publication Date: 2018-08-15
    Description: Mass transfer rates of many gases, nutrients, and trace metals across the sediment water interface are dependent on environmental oxygen conditions. In this article, a novel gas exchange system for extended in situ flux and respiration measurements in benthic chambers under defined oxygen conditions is described. Integrated within a GEOMAR modular lander, the gas exchange system was used to perform in situ measurements of the total oxygen uptake and sea bed methane emission rates under constant oxygen conditions at Captain Arutyunov mud volcano (Gulf of Cadiz) in a water depth of 1320 m. During two separate lander deployments, the oxygen concentration within the benthic chambers was kept constant for 37 and 47 h, respectively. Under these conditions total oxygen uptake rate remained constant at 4.4 and 13.2 mmol m�2 d�1. Seabed methane emission was low, in the range 0 to 0.2 mmol m�2 d�1. The system is suited for prolonged (days) in situ flux determinations under natural background oxygen conditions and offers a wide range of experimental applications
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.4319/lom.2008.6.23
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 6
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    Rotifers colonising sediments with shallow gas hydrates (2003)
    Springer
    In:  Naturwissenschaften, 90 . pp. 273-276.
    Details
    Publication Date: 2017-03-07
    Description: Rotifers, one of the smallest metazoans, are only seldom found in marine environments. Surprisingly, we discovered high abundances of at least two new species of rotifers settling in anoxic and highly sulphidic sediments associated with shallow gas hydrates (GH) at the southern crest of Hydrate Ridge off Oregon, NE Pacific, in a water depth of about 780 m. At basins adjacent to Hydrate Ridge, 1,285–2,304 m deep, we found rotifers co-occurring with the sulphide-oxidising bacteria Thioploca sp.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1007/s00114-003-0423-6
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 7
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    Coupling between phytodetritus deposition and the small-sized benthic biota in the deep Arabian Sea: analysis of biogenic sediment compounds (2000)
    Pergamon Press
    In:  Deep Sea Research Part II: Topical Studies in Oceanography, 47 (14). pp. 2805-2833.
    Details
    Publication Date: 2020-08-05
    Description: As part of the large-scale, interdisciplinary deep-sea study “BIGSET”, the relationship between the monsoon-induced regional and temporal variability of POC deposition and the small-sized benthic community was investigated at several sites 2316–4420 m deep in the Arabian Sea during four cruises between 1995 and 1998. Vertical and horizontal distribution patterns of chloroplastic pigments (a measure of phytodetritus deposition), readily soluble protein and activity, and biomass parameters of the small-sized benthic community (Electron Transport System Activity (ETSA); bacterial ectoenzymatic activity (FDA turnover) and DNA concentrations) were measured concurrently with the vertical fluxes of POC and chloroplastic pigments. Sediment chlorophyll a (chl. a) profiles were used to calculate chl. a flux rates and to estimate POC flux across the sediment water interface using two different transport reaction models. These estimates were compared with corresponding flux rates determined in sediment traps. Regional variability of primary productivity and POC deposition at the deep-sea floor creates a trophic gradient in the Arabian Basin from the NW to the SE, which is primarily related to the activity of monsoon winds and processes associated with the topography of the Arabian Basin and the vicinity of land masses. Inventories of sediment chloroplastic pigments closely corresponded to this trophic gradient. For ETSA, FDA and DNA, however, no clear coupling was found, although stations WAST (western Arabian Sea) and NAST (northern Arabian Sea) were characterised by high concentrations and activities. These parameters exhibited high spatial and temporal variability, making it impossible to recognise clear mechanisms controlling temporal and spatial community patterns of the small-sized benthic biota. Nevertheless, the entire Arabian Basin was recognised as being affected by monsoonal activity. Comparison of two different transport reaction models indicates that labile chl. a buried in deeper sediment layers may escape rapid degradation in Arabian deep-sea sediments.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/S0967-0645(00)00050-3
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 8
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    Metazoan meiofauna of the deep Arabian Sea: Standing stocks, size spectra and regional variability in relation to monsoon included enhanced sedimentation regimes of particulate organic matter (2000)
    Pergamon Press
    In:  Deep Sea Research Part II: Topical Studies in Oceanography, 47 (14). pp. 2957-2977.
    Details
    Publication Date: 2020-08-05
    Description: Effects of monsoon-induced enhanced depositional regimes of particulate organic carbon (POC) on regional variability and distribution patterns and size spectra of metazoan meiofauna, particularly of nematodes, were investigated at five sites 3158–4414 m deep in the Arabian Sea. The sampling sites were subjected to different flux rates of POC. Total meiofaunal abundance ranged from 109 to 320 ind./10 cm2. Nematodes were the numerically most abundant taxon, with a relative abundance of 82.5–88.7%, followed by copepods and ostracods. Mean individual nematode biomass ranged from 0.0272 to 0.1033 μgC, and Mean nematode population biomass varied between 0.0026 and 0.0133 mgC/10 cm2. Mean nematode lengths ranged from 614.2 to 832.6 μm. The length distributions of nematodes at the different sites were typically skewed with the distributions extending into the longer size classes. At the sites with higher POC deposition rates, nematodes displayed deeper distributions in the sediment column (47.4–58.5% of nematodes in the top 1 cm layer of the sediment) in contrast to very shallow distributions at a site of low POC flux (75.1% of nematodes in the top 1 cm of the sediment). Regional variability of nematode biomass, size and vertical distribution was related to monsoon-driven gradients of POC- and chlorophyll a (chl. a) flux rates and bacterial biomass i.e. bioavailable organic carbon. This was in contrast to nematode abundance which did not correlate significantly with any of these environmental parameters. The differential pattern between biomass and abundance, distribution might be related to POC-dependent alterations in the species composition of the nematode assemblages at the different sites. The hypothesis of increased meiobenthic stocks due to monsoon-induced enhanced sedimentation could not be confirmed compared to data from other less productive oceanic regions. Nematode abundance and biomass in the Arabian Sea were similar to values obtained from the abyssal temperate NE-Atlantic.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/S0967-0645(00)00054-0
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    OceanRep: Article in a Scientific Journal - peer-reviewed
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