Ref ID : 625
Taylor, W.D. and D.R.S. Lean; Radiotracer experiments on phosphorus uptake and release by limnetic microzooplankton. Can.J.Fish Aquat.Sci. 38:1316-1321, 1981
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When carrier-free [32]PO4 is added to lake water, the planktonic ciliated protozoan Strombidium viride gradually becomes labeled over at least 30 hr. The label enters S. viride primarily by the ingestion of labeled particles 0.2-1.0 µm in size; direct uptake of phosphate or uptake of larger particles (>5 µm) is relatively slight or absent. When labeled S. viride are transferred to unlabeled lake water, they lose [32]P by a discontinuous process, presumed to be defecation, plus a relatively slow, continuous process. The latter is assumed to be equivalent to what is usually termed excretion for crustacean zooplankton, and is equivalent to a turnover time for the animal's phosphorus content of many hours. Results of release experiments with the rotifer Keratella cochlearis are quantitatively similar, but defecation was a much larger part of the total. Excretion was similar in turnover time to that for S. viride. The soluble phosphorus released by both species was characterized as primarily phosphate using gel filtration. These results do not support the conventional view that microzooplankton regenerate dissolved phosphorus much more rapidly for their biomass than larger crustacean zooplankton.