Bacterial dynamics of the Patos Lagoon estuary, southern Brazil (32°S, 52°W): relationship with phytoplankton production and suspended material

Abstract

A field study of the microbial food web was conducted in a shallow region of the Patos Lagoon estuary (32°07′S; 52°06′W) between March 1989 and March 1990. On average, bacterial biomass (mainly attached bacteria) constituted 35·8% of the particulate organic carbon (POC) and exceeded phytoplankton biomass for several months. Bacterial growth, measured as the frequency of dividing cells (FDC), was significantly correlated with phytoplankton production (r = 0·70, p < 0·01), however, no relationship was observed between bacterial abundance and phytoplankton parameters. Attached bacteria abundance was poorly correlated with the amount of seston. In addition, forced resuspension of sediments within enclosures connected to the lagoon bed, showed that this was an unlikely mechanism contributing to an increased abundance of attached bacteria in the overlying water. Bacterial community dynamics appear to be mainly determined by biological factors such as primary production and protozoan grazing. A reduction in bacterial cell volume concurrent with an increase in cell numbers is proposed as a possible response to counteract the effects of protozoan grazing.