Abstract

A propagule experiment was designed to investigate the effects of different food types and varying sediment depths on the survival and growth of upper-bathyal benthic foraminifera, collected from surface-sediment cores in Oslofjord, Norway. Sediment that passed through a 53-μm sieve was used in the experiment. Any foraminifera >63 μm at the end of the experiment had therefore grown, indicating at least tolerable living conditions. The experiment was arranged into four sub-experiments to test foraminiferal responses to a lack of food input, algal medium, sediment depth (1- vs. 2-cm depth), and different food types. Potential food sources included monospecific algal cultures (the green alga Dunaliella tertiolecta, the haptophyte Emiliania huxleyi, and the diatoms Chaetoceros sp. and cf. Navicula), as well as phytoplankton and zooplankton from net hauls collected at the same sampling site. After six weeks all foraminiferal assemblages showed an increase in abundance, even those which were not fed. This suggests that most species (e.g., Textularia earlandi, Bathysiphon flexilis) were feeding on microbes or detritus already in the sediment. However, the addition of certain phytodetritus increased the abundance, suggesting that some species (e.g., Epistominella vitrea) are dependent on the input of this particular fresh phytodetritus. Conversely, certain types of detritus (E. huxleyi and zooplankton) appear detrimental to most species, except Elphidium excavatum which appeared resistant to the treatments inimicable to other species. Leptohalysis catella was the only species observed to respond positively to net hauls dominated by dinoflagellates. For some species (e.g., Stainforthia fusiformis, Nonionella iridea) the availability of a greater sediment depth stimulates growth more than the input of organic matter.

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