BACTERIAL AND PHYTOPLANKTON PRODUCTION IN TWO COASTAL SYSTEMS INFLUENCED BY DISTINCT EUTROPHICATION PROCESSES

Resumo

Evaluating the relationships between bacterial (BP) and phytoplankton production (PP) is a first step to understand carbon fluxes through pelagic food webs. In the present study, BP and PP were compared at two tropical coastal systems influenced by distinct eutrophication processes in order to assess the main regulating factors of particulate organic carbon (POC) production rates. The waters of Cabo Frio region (23^o00'S; 42^o 00'W) present high nitrate (N-NO₃) levels and low temperatures resulting from the upwelling of deep water masses -- thus, a natural eutrophication process -- while the waters in Guanabara Bay (22^o54'S; 43^o09'W) present high temperatures and levels of dissolved organic carbon (DOC), nitrogen (DON) and nutrients (other than nitrate),resulting from anthropogenic eutrophication, mainly because of sewage wastes. Dissolved organic matter (DOM) elemental composition indicates lower autochthonous contribution in Cabo Frio (C:N ~ 42), probably due to lower phytoplankton production. The elevated temperatures in Guanabara Bay yielded higher PP rates, increasing the phytoplankton contribution to the DOM pool which improved BP. No coupling between BP and PP was observed, and POC production was mainly due to phytoplankton in both systems.