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Living dangerously: implications of hydrogen sulphide events for marine life along the Namibian coast: A.G.V. Salvanes6, R. Bahlo5
Stockholm University.
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2008 (English)In: International Symposium on Eastern Boundary Upwelling Ecosystems: Spain, 2008Conference paper, Published paper (Other (popular science, discussion, etc.))
Abstract [en]

Hypoxia, anoxia and free hydrogen sulphide in the water column are characteristic of the inner shelf coastal upwelling system off central Namibia. Biogeochemical monitoring of the diatomaceous sediments along the central coast over a 3-year period, coupled with acoustic studies and ROV video coverage, indicated a major role played by the seafloor in the generation and control of H2S into the water column. We determined the sedimentary processes resulting in the generation and dispersal of hydrogen sulphide, and its effect on some of the locally important fishes and invertebrates.

Marked interannual variability with no obvious seasonal trends was apparent in methane contents of sediments even over the short three-year period, whilst sulphate reduction rates in the sediment showed little change. The large sulphur bacteria Thiomargarita namibiensis and Beggiatoa spp. form dense mats over extensive areas of mud and oxidize sulphide at the sediment-water interface, thereby regulating its flux into the overlying water. During episodic events however, hydrogen sulphide pervades the entire water column, followed by severe hypoxia. Under experimental conditions, the survival of juvenile horse mackerel Trachurus trachurus capensis was limited to less than two hours in water containing <0.7ml.l-1 dissolved oxygen. If sulphide was also present survival time was reduced to less than 30 minutes. In contrast, pelagic gobies Sufflogobius bibarbatus survive exposure to extended periods of anoxia and water containing sulphide. Gobies are found abundantly on the muddy seafloor where they evidently possess both physiological and behavioural strategies to survive sulphide and anoxia, accounting for the success of this species in Namibian waters and its importance as a key diet species for predatory fish, seabirds and marine mammals.

Place, publisher, year, edition, pages
2008.
Keyword [en]
hydrogen sulphide, hypoxia, anoxia, methane, Northern Benguela, Namibia, large sulphur bacteria, pelagic goby
Identifiers
URN: urn:nbn:se:su:diva-15797OAI: oai:DiVA.org:su-15797DiVA: diva2:182317
Available from: 2008-12-10 Created: 2008-12-10Bibliographically approved

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