Oxygen-minimum zone sediments in the northeastern Arabian Sea off Pakistan : a habitat for the bacterium Thioploca

• 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: Oldendorf Inter-Research 01-01-2001
• Subjects: Animal, plant and microbial ecology; Beggiatoa; Biological and medical sciences; Fundamental and applied biological sciences. Psychology; General aspects; Marine; Microbial ecology; Pakistan; sulfur-oxidizing bacteria; Thioploca; Indian Ocean; Arabian Sea; ISW, Pakistan, Balochistan; ISW, Arabian Sea, Makran Accretionary Prism; ISW, Arabian Sea; Morphological variation; Minimum; Oxygen; Beggiatoaceae; Reduction rate; Carbon dioxide; Environmental factor; Sulfates; Sediments; Spatial variation; Depth; Coastal zone; Marine environment; Cold seep; Sulfides; Fixation; Thioploca; Bacteria; Beggiatoales; Ecological abundance
• ISSN: 0171-8630; 1616-1599
• DOI: 10.3354/meps211027

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 bacterium Thioploca in near-surface layers between 0 and 13 cm depth. Thioploca bundles were up to 20 mm in length and contained up to 20 filaments of varying diameters, between 3 and 75 mu m. Up to 169 ind. cm super(-2) were counted. Maximum numbers occurred in the top 9 cm of sediment, which contained very low concentrations of soluble sulfide (<0.2 mu M) and high amounts of elemental sulfur (up to 10 mu mol cm super(-3)). Moderate sulfate reduction activity (between 20 and 190 nmol cm super(-3) d super(-1)) was detected in the top 10 cm of these sediments, resulting in a gradual downcore decrease of sulfate concentrations. CO sub(2) 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 of Thioploca and of the geochemical setting are discussed and compared to other sites containing Thioploca communities.