Phosphatase activity and plankton dynamics in two tropical coastal lagoons

We investigated whether phosphatase activity (PA), measured with p-nitrophe nylphosphate as a substrate, is coupled to nutrient concentrations and the biomass of phytoplankton and bacterioplankton in two tropical coastal lagoo ns (Imboassica and Cabiunas Lagoons, Brazil). We also evaluated whether the supply of inorganic phosphorus to plankton communities is satisfied by the hydrolysis of organic compounds catalysed by PA. In Imboassica Lagoon, hyd rolysis of organic phosphate by PA was a significant source of inorganic ph osphorus for the plankton, and PA was correlated with phytoplankton biomass . In Cabiunas Lagoon, PA was not a significant source of inorganic phosphat e for phytoplankton, and variations in PA were associated with changes in b acterial biomass. Differences between these lagoons were attributed to diff erences in the quality of dissolved organic matter.