An experimental study on the proxy value of benthic foraminifera : the impact of physical disturbance, oxygen depletion and organic flux

Abstract

The preparation of the laboratory experiments, e.g., sieving, causes physical disturbance to the foraminifera. In Chapter 2 we studied the effects of such disturbance by observing individual living specimens. Observations were made on individuals from three different areas: the Wadden Sea, the Adriatic Sea and the Bay ofBiscay. We sieved sediments from which we handpicked individual specimens. We used for the observations an inverted-light microscope with phase-contrast filter to which a video camera was connected to make recordings. Specimens from the intertidal area (Wadden Sea), and especially the epifaunal to shallow infaunal taxa, showed to be very active and able to survive the transport and sieving treatments. The taxa from deeper environments, Adriatic Sea and Bay of Biscay, were less active, and deep infaunal taxa showed no pseudopodial activity. It can well be that a general relation exists between pseudopodia! activity on the one hand, and environment and the vertical depth of the habitat on the other. Taxa living in high-energy environments and occupying shallow infaunal or epifaunal microhabitats, display the highest pseudopodia! activity. More detailed observations were made on the morphology of pseudopodia! networks. Groups of taxa could be distinguished based upon pseudopodium characteristics. Variation between these groups was seen in the density, shape ofand connections between the pseudopodia. This ranged from taxa with a dense and strongly branched pseudopodium to taxa with only a few thin and long pseudopodia. Part of the observations focussed on locomotion and they showed that different modes existed. Planispiral taxa rotate almost continuously while moving, whereas miliolid, uni-, bi- and triseria! taxa move in a more linear way. Potential important negative effects oflight on the pseudopodia] activity of certain foraminifera ""ere demonstrated by the observation of an allogromiid specimen. This specimen showed a strong sensitivity for intense light, which made the specimen to cease all pseudopodia! activity. Finally, a number of observations dealt with the disturbance of pseudopodial networks of some taxa. Using a brush, parts of the pseudopodium were separated from the rest of the organism, fonning so-called pseudopodial satellites. These satellites were capable of surviving in a petri dish, depending upon their size for how long. Often the satellites formed a central body from which small pseudopodia were extended. When brought in contact with the pseudopodium of the parent organism, they fused and the satellite formed again part of the organism. Satellites from other specimens of the same or of other taxa did not merge with the pseudopodium but were transported into the test, perhaps ro be used as food.