An analysis of metabolic characteristics of planktonic heterotrophic protozoans

Respiration rate data on 61 heterotrophic planktonic protozoans were compiled and analyzed as a function of body mass [wet mass (WM), dry mass (DM), carbon (C) or nitrogen (N)], temperature, measuring method (Cartesian divers, Warburg, and electrodes, among others), physiological condition (growing, starved or unspecified) and taxon (amoebae, flagellates or ciliates). Stepwise multiple-regression analyses revealed that body mass was the most important parameter, followed by the physiological condition and temperature. The taxon-specific effects of body mass were detected for ciliates. Overall, the regression models explained 84% of the variance of the respiration data. Similar analyses could not be performed for the rates of ammonia excretion because of insufficient data. The comparison of the regression line of the respiration rates on WM and that of the ammonia excretion rates on WM, both of growing heterotrophic protozoans, yielded an O:N ratio of 7.2, which indicates protein-oriented metabolism. A comparison of the results of this study with the routine respiration rates of marine pelagic metazoans showed that the rates of growing protozoans were lower (0.71fold) than those of crustaceans and fishes based on WM but were equivalent to those based on C mass.