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キーワード:
Ciliata; Abundance; Biomass; Seasonal distribution; Depth distribution; Size classes
要旨:
Ciliata in sandy bedsediments of the Breitenbach were studied quantitatively. The Breitenbach is an unpolluted foothill stream in Hesse, Germany, which runs through an area of fine-grained sandstone. The stream lacks a porous, continuously oxygenated, hyporheic zone. Sediment cores were collected at monthly intervals, from September 1990 to August 1991, at four sites along the stream, to depths of 10 cm. They were subdivided into 2 cm layers, and live Ciliata were counted directly in diluted samples. Their abundance varied greatly, the observed maximum being about 4000/ml sediment in March 1991. There was no longitudinal gradient of ciliate abundance, and it showed no clear seasonal pattern at one site; but at the other three sites it peaked in spring and early summer. At two sites, bacterivorous Ciliata were normally dominant, but peak abundances resulted from increased numbers of herbivorous species. Depth distribution of Ciliata peaked in the 0-2 cm sediment layer. Some so-called sapropelic taxa (genera Metopus, Brachonella and Caenomorpha) were normally observed only below 2 cm depth; but during periods of low discharge they also occurred in the top layer of sediment. Biomass was up to 170 µg wet weight/ml sediment. Small ciliata (<60 μm) were strongly dominant all the time, and seasonal variation of biomass was essentially parallel to numerical abundance.
