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Revista Chilena de Historia Natural 81 (3): 403-416, 2008
Living (stained) calcareous benthic foraminifera from recent sediments off Concepción, central-southern Chile (~36º S)
This study examines onshore-offshore and vertical distribution of living (Rose Bengal stained) benthic foraminifera (> 180 µm fraction) from three sediment stations along a bathymetric transect off Concepción, Chile (station 18 = 88 m water depth, station 26 = 120 m, station 40 = 1,030 m), within and below the oxygen minimum zone. All cores were collected in austral winter. Calcareous foraminifera dominated the three stations. The species composition, living foraminiferal density, and vertical distribution patterns within the sediment changed in accordance with bottom water dissolved oxygen concentration and food availability. Onshore-offshore pattern revealed overall highest living foraminiferal densities at shelf stations 18 and 26 where bottom water dissolved oxygen was lowest (~ 0.2 mL<sup>-1</sup>) and content in labile organic matter highest. Within the sediment, maximum relative abundances (50-60 %) of living organisms were found in the 0-1 cm interval at the organic-rich and oxygen-poor shelf stations 18 and 26. In the well-oxygenated (2.7 mL<sup>-1</sup>) slope station 40, 70 % of living foraminifera were observed deeper than the first centimeter. The number of species and the contribution of the > 250 αm fraction to the total fauna larger than 180 µm increased offshore. Nonionella auris (d’Orbigny) dominated at stations 18 and 26 while a more diverse foraminifera fauna was found at station 40. This study provides the first quantitative data on living benthic foraminifera in the area; seasonal and interannual changes are not addressed.
Key words:
benthic foraminifera, sediments, oxygen minimum zone, Concepción, Chile

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