Carbon utilization by the omnivorous flagellate Paraphysomonas imperforata

Abstract

Carbon utilization by the omnivorous microflagellate Paraphysomonas imperforata was examined when this protozoan was fed either of two species of algae grown to three degrees of nitrogen limitation and three degrees of phosphorus limitation. Carbon incorporation (retention in the particulate fraction) by the microflagellate differed slightly for the two prey species but was a constant percentage of the total carbon budget of the protozoan for each prey alga (i.e. the degree of nitrogen or phosphorus deficiency of the algae did not affect carbon incorporation by the protozoan). The patterns of respiration in the six grazed cultures of each alga were also similar. Carbon incorporation and other nutrient utilization by this protozoan apparently were uncoupled to achieve this result. Firm conclusions are equivocal due to the possible dark uptake of nutrients by the algae. Our results are consistent, however, with a mathematical model in which the nutrient excretion rate is predicted from the respiration rate and gross growth efficiency of the protozoan and the C : N : P ratios of the protozoan and its prey.