Oxygen-minimum zone sediments in the northeastern Arabian Sea off Pakistan a habitat for the bacteriumThioploca

• Published in: Marine ecology. Progress series (Halstenbek) Vol. 211; pp. 27 - 42
• Main Authors: Schmaljohann, Rolf, Drews, Manuela, Walter, Sylvia, Linke, Peter, von Rad, Ulrich, Imhoff, Johannes F.
• Format: Journal Article
• Language: English
• Published: Inter-Research 14-02-2001
• Subjects: Bacteria; Beggiatoa; Biofilms; Nitrates; Seas; Sediments; Sulfates; Sulfides; Sulfur; Water depth
• ISSN: 0171-8630; 1616-1599

Filamentous sulfur-oxidizing bacteria and geochemical parameters of sediments at the Makran accretionary wedge in the northeastern Arabian Sea off Pakistan were studied. The upper continental slope between 350 and 850 m water depth, which is in the center of the oxygen-minimum zone, is characterized by numerous sites of small-scale seeps of methane- and sulfide-charged porewater. White bacterial mats with diameters <1 m were discovered at the surface of these sites using a photo-TV sled. Seep sediments, as well as non-seep sediments, in the vicinity were characterized by the occurrence of the bacteriumThioplocain near-surface layers between 0 and 13 cm depth.Thioplocabundles were up to 20 mm in length and contained up to 20 filaments of varying diameters, between 3 and 75 μm. Up to 169 ind. cm–2were counted. Maximum numbers occurred in the top 9 cm of sediment, which contained very low concentrations of soluble sulfide (<0.2 μM) and high amounts of elemental sulfur (up to 10 μmol cm–3). Moderate sulfate reduction activity (between 20 and 190 nmol cm–3d–1) was detected in the top 10 cm of these sediments, resulting in a gradual downcore decrease of sulfate concentrations. CO₂ fixation rates had distinct maxima at the sediment surface and declined to background values below 5 cm depth. The nutritional implications of the distinct morphology ofThioplocaand of the geochemical setting are discussed and compared to other sites containingThioplocacommunities.