MEPS 246:85-94 (2003)  -  doi:10.3354/meps246085

Effect of anoxia on the vertical migration of benthic foraminifera

I. A. P. Duijnstee1,2,*, S. R. Ernst1,2, G. J. van der Zwaan1,2

1Department of Geology, Institute of Earth Sciences, Utrecht University, Budapestlaan 4, 3584 CD Utrecht, The Netherlands
2Department of Biogeology, Faculty of Sciences, University of Nijmegen, Toernooiveld 1, 6525 ED Nijmegen, The Netherlands

ABSTRACT: We present the results of a microcosm experiment in which benthic foraminifera had to re-establish microhabitat distributions under simulated anoxic and oxygenated bottom-water conditions after initial homogenization of the sediment (obtained from the northern Adriatic Sea at 32 m water depth). After 3 wk, the vertical distribution of the 12 most abundant species was assessed. These taxa could be divided into 2 distinct groups: (1) typical shallow-living species with maximum abundances in the top 2 cm of the sediment; and (2) deeper-dwelling taxa that were more homogeneously distributed throughout the sediment column. Compared to the oxygenated environment, the average living depth of all species was less under anoxic bottom-water conditions in which the group of shallow dwellers was almost restricted to the top 5 mm of the sediment. This distribution was most probably caused by negative geotaxis, induced by an external stimulus associated with anoxic conditions (e.g. high [H2S]). The deeper-living taxa apparently lack the ability for negative geotaxis or are less sensitive to the stimulus.

KEY WORDS: Living benthic foraminifera · Vertical distribution · Vertical migration · Anoxia · Negative geotaxis · Microcosm experiment

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