Effects of disturbance on phosphorus turnover and plankton dynamics

In coastal lagoons, one common type of anthropogenic disturbance is opening of the sand barriers that isolate these lagoons from the sea. We investigated how a disturbance caused by an artificial opening of the sand barrier affects phytoplankton and bacterioplankton dynamics and alkaline phosphatase activities (APA) in a Brazilian coastal lagoon. We propose an index of potential phosphorus turnover time (PPTT) calculated as the ratio of total phosphorus (TP) and APA in an attempt to quantify the effect of disturbances on phosphorus recycling within the plankton community. Opening the barrier caused increased phytoplankton biomass, TP concentrations, APA and PPTT, and decreased bacteria to phytoplankton biomass ratio. PPTT is easily calculated and may be used to detect plankton responses to anthropogenic disturbances.