Foraminifera are a dominant group of amoeboid protists in the deep-sea and play possibly a significant role in decomposition processes of incoming organic matter. In order to study the poorly known ecology of these protozoans, microcosm experiments with living bathyal benthic foraminifera have been conducted. Foraminifera from 2880 m and shallower water depths were successfully maintained and their movement patterns investigated. By video documentation, high mean migration speed of 20,02 (N = 22) and 24,48 /Lm min-1 (N = 10) at 4 DC were found for species such as Hoeglundina elegans and Quinqueloculina seminula from 1847 m and 1921 m water depth, respectively. The results demonstrate that some bathyal foraminifera have migration speeds comparable to those of shallow water species. Environmental factors such as temperature, food concentration and oxygen content showed a marked influence on the migration of some species. An increase in temperature from 10 DC to 15 DC resulted in an increase of 35% in the migration speed of Allogromia spp. However, other species reacted differently. Higher food concentration resulted in a decrease in speed of some species. While in Quinqueloculina lamarckiana speed was not greatly affected by a low oxygen content in the sediment, other foraminifera responded to oxygen depletion by migration to the surface layers. Observations of benthic foraminifera in the laboratory microcosms are discussed in relation to microhabitats and the fate of organic matter on the sea floor and in the sediment.

Despite their small size, foraminifera often reach high standing stocks and play a significant role in structuring the top layers of the sediment. However, the behavioral and ecological interactions of foraminifera with the surrounding sediments have been rarely investigated. In order to study these poorly known aspects of foraminiferal ecology, living foraminifera from bathyal and shallower water depths were successfully maintained in microcosms and their relationship with the sediment was investigated. Sediment-interactions of foraminifera take part mainly as a result of 1) locomotion, 2) deposit feeding with ingestion and egestion within different sediment layers, thus causing constant bioturbation, and 3) the use of particles for the formation of cysts for feeding, reproduction, chamber building or protection. Movement by foraminifera results in the ventilation of the sea floor as demonstrated by the active and passive transport of luminescent particles. From the experiment conducted, a high mixing rate (Db ഠ 0.2 cm 2 /day) for the foraminiferal assemblage was calculated. Thus, benthic foraminifera contribute significantly to the bioturbation of surface sediments. These observations are discussed in relation to microhabitats and the fate of organic matter at and below the sediment-water interface.

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