Continuous flow microcosms (50L volume, salinity 18-24 ppt) were used to examine the roles of heterotrophic protozoa and bacteria as phosphorus mineralizers. Nitrogen limitation was regulated by N:P supply ratios (5:1, 16:1) and growth rate was regulated by dilution rate (0.5, 0.25 volumes day&\sp{lcub}-1{rcub}&). Rates of carbon and phosphorus uptake from dissolved inorganic pools were determined using &\sp{14}&C and &\sp{lcub}32{rcub}&P tracer experiments and pre- and post-fractionation incubations. Based on uptake rates and on POP and POC values of the bacteria in the &\u3c&1.0 &\mu&m fraction, mass balance estimates of bacterial mineralization were determined. An isotope dilution method was used to determine phosphorus mineralization in the unfractionated sample. Heterotrophic protozoan mineralization was calculated as the difference. Results showed that bacteria had a minor role as remineralizers of phosphorus, more often taking-up inorganic phosphorus than remineralizing it. Heterotrophic protozoa were the major remineralizers of phosphorus. Microcosm treatments with a greater supply of inorganic phosphorus over nitrogen had increased POP concentrations and increased phosphorus remineralization. The effect of dilution on phosphorus remineralization was temperature dependent. Greater remineralization occurred in the high dilution rate in the July through October experiments and less remineralization occurred in the high dilution rate treatments in the December and January experiments
