Phosphorus Regeneration in Fresh‐Water Paramecia*

SYNOPSIS Turnover rates of soluble phosphorus (P) by Paramecium multimicronucleatum were compared under 3 temperature regimes. Phosphorus uptake by this heterotroph was almost completely dependent on consumption of bacteria rather than direct uptake of soluble 32 PO 4 . Phosphorus uptake rates by P. bursaria when in its autotrophic state (a symbiotic relationship with zoochlorellae) and when in its heterotrophic (bacteria feeding) state were also compared. Paramecium bursaria showed a much higher uptake of P when large numbers of labeled bacteria were present than when they were absent. Phosphorus turnover rates by P. bursaria were determined and compared with those of P. multimicronucleatum. These ciliates showed remarkably rapid turnover rates for soluble P. In each case turnover rates were universely related to biomass. Ciliates, although small, have very high metabolic rates and therefore may be important for nutrient regeneration in our fresh‐water lakes, streams, and ponds.