Feeding by Cyclidium Sp. (Ciliophora, Scuticociliatida) on Particles of Different Sizes and Surface Properties
Abstract:The effect of size, surface properties, and concentration of food particles on feeding by the scuticociliate Cyclidium sp. was investigated. A range of particle sizes at concentrations bracketing natural picoplankton densities (1·104 to 5·108·ml−1) was offered to the ciliates. Uptake of microspheres and of single cells of the cyanobacterium Microcystis aeruginosa was directly related to feeding time for up to 15 minutes. Clearance rates on 0.6 µm microspheres were always higher than for 0.93 µm microspheres when compared for similar concentrations or volumes offered. Maximum clearance on 0.93 µm spheres was at an intermediate sphere concentration. This atypical functional response was due to a change in swimming behavior which reduced ingestion at low concentrations of 0.93 µm spheres. When Cyclidium was offered either carboxylated or protein-coated 0.6 µm microspheres, there was no significant difference in clearance rates at any particle concentration. However, clearance rates on 0.93 µm protein-coated spheres were significantly greater than on the same size carboxylated spheres at concentrations < 108·ml−1. The electrophoretic mobilities (e.m., an indicator of surface charge) of protein-coated and carboxylated spheres were significantly different. Clearance rates on carboxylated and amide-modified spheres (0.93 and 0.94 µm, respectively) were similar whether they were offered alone or together at concentrations between ∼4·105 and 8·105·ml−1. Carboxylated and amide-modified spheres had similar e.m. These data suggest that interactions between food particle size, concentration, and surface properties alter behavior and food capture by Cyclidium in a complex manner. Use of fluorescent microspheres of the same size, but with different coatings, has the potential for elucidating feeding behavior by protozoa in the laboratory and ultimately in situ, where the prevalence of selective feeding by protozoa has direct bearing on regulation of picoplankton community structure.
Document Type: Research Article
Publication date: November 1, 1988
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