Abstract
Foraminifera are unicellular organisms that are abundantly present in the marine realm. They inhabit both the water column as well as the sediment; these latter (benthic) foraminifera are the main subject of this thesis research. They have a high fossilisation potential, and for that reason they have become valuable proxies
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in paleoecological studies. In modern sediments their role in the ecosystem is considerable. This has been ignored for a long time and it is only since the last few decades that living foraminifera have attracted interest. Predominant regulating factors of benthic foraminiferal occurrence and microhabitat selection are oxygen and organic flux. The relationship between these two factors and microhabitat selection has been described in the TROX model (Jorissen et al., 1995). An amended version of the model (TROX-II; Van der Zwaan et al., 1999) also incorporated the effect of redox zones. Although specific food preferences of foraminifera are far from understood, many different strategies of feeding have been found. Some foraminifera are dependent on algae as symbionts and possible even bacteria, although the latter interaction has not been properly studied sofar.
Recent studies suggest that bacterial activity might be important in foraminiferal distributions. Since redox zonation plays a prominent role in benthic foraminiferal ecology, the importance of bacteria is undisputed. However, the relative importance of redox conditions versus bacteria in foraminiferal ecology is unclear.
In this thesis research the foraminiferal – bacterial interaction was addressed in several experimental studies as well as in a field study. We aimed at developing an experimental setting that is suitable for both foraminiferal and bacterial research. We also aimed at obtaining more insight in the bacterial impact on redox processes that occur in the sediment and their ensuing influence on foraminifera.
In short the following results were obtained. Bacteria are suggested to have a major influence on foraminiferal microhabitat selection. The occurrence of specific bacterial activities seems to be more important than an obvious change in redox conditions. The way bacteria influence foraminifera is still an open question. Our research also provided some answers concerning the regulating factors of foraminiferal microhabitat selection. Although shallow living taxa are quite conclusively dependent on the oxygen concentration (see also Duijnstee, 2001), the reactive responses of deeper living foraminifera are far more complex. In the deeper redox zones different taxa show a different reaction to environmental factors such as food and bacterial activity.
For the improvement of the proxy value of these deeper living foraminifera research as described in this thesis is essential. It makes a start at understanding the dependence of these deeper living foraminifera on bacteria and redox zonations. This knowledge is essential to better assess disturbances in the deeper marine microniches and food chains. In turn, this will lead to a much better insight into biogeochemical cycling and the role of meiofauna in this context. Especially the effect of grazing by meiofauna (i.e. foraminifera) on bacterial flux, and thus on biogeochemical cycling, would deserve attention
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