Next, one treatment, in which cells of B comatum ingested no mor

Next, one treatment, in which cells of B. comatum ingested no more than one particle per cell on average, was chosen for analysis. All bottles with sea water (200 ml each) were incubated for half an hour on an anchored

experimental set-up deployed in the coastal zone of the Baltic Sea. All experiments were carried out between 11:00 and 14:00 hrs (around noon). Samples were HDAC inhibitor taken before and after the incubations and immediately fixed with acid Lugol’s solution (a low concentration – 0.5%). Samples were stored in a refrigerator (4°C) and analysed under an inverted microscope (Utermöhl 1958) within one month. All measurements were done manually with the image analysis system. Starch particles inside ciliates were categorized into 8 size classes: 1.25 μm, 2.50 μm, 3.75 μm… 10.00 μm (as above). Because some B. comatum cells contained dark inclusions prior to incubation (most probably food particles like flagellates), two analyses were performed:

before and after incubation, the difference being treated as due to starch particles ingested during the experiment. Typically, 50–70 cells in every sample were analysed (the minimum number of specimens was 23). Additionally, the abundance of natural food – nanoflagellates – was determined in the samples taken before experimental incubations. This was done under GSI-IX an epifluorescence microscope after staining with primulin ( Caron 1983). Balanion comatum ingested particles ranging from 1.25 μm to 6.25 μm, and preferably from two size classes, 2.50 μm and 3.75 μm. Because of the classification into arbitrary size classes, the preferred particle size in practice ranged from 1.9 to 4.4 μm. The clearance rate for the whole range of particles ingested generally rose from 1.4 to 6.4 μl cell−1 h−1 with a temperature increase from 8 to 19°C ( Figure 1); however, the dependence was non-significant (both linear and exponential models). Consistently higher estimates (Wilcoxon’s signed rank test, p = 0.04)

were obtained for particles of preferred size (1.9–7.0 μl cell−1 h−1, the same temperature range). This clearance rate (for preferred particles) rose significantly with temperature ( Table 1). The linear approximation was statistically highly significant (R2 = 0.91, Rapamycin ic50 p = 0.01), whereas the exponential model yielded a lower significance (R2 = 0.86, p = 0.02). Q10 calculated with the exponential model amounted to 2.9 and lay within the range of typical values. As the studies were carried out under natural conditions (temperature, irradiance, wave motion), the measured clearance rates were most probably very close to the natural ones. Starch particles are typically used as a surrogate food for oligotrichs and choreotrichs (Heinbokel 1978, Kivi & Setälä 1995), that is, filter-feeders that ingest particles rather unselectively.

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