Dinâmicas do picoplâncton na Costa Oeste do Oceano Atlântico Equatorial

Abstract

Most of the ocean’s biomass is microbial and picoplankton microorganisms, which consists of small cells (<3 µm), are central players of global nutrient cycle and C production. Heterotrophic bacteria, cyanobacteria (e.g. Synechococcus and Prochlorococcus) and autotrophic picoeukaryotes comprise the picoplankton and often dominate plankton in low-latitude oligotrophic oceans. Evaluate temporal dynamics of these organisms is critical to understand microbial stocks and C fluxes in the tropical ocean. Thus, we performed monthly samplings between 2013-2016 at the Equatorial Atlantic Microbial Observatory (EAMO) sampling station located on the coast of RN state – Brazil to evaluate time variations in abundance, biomass and activity (bacterial production and respiration) of picoplankton assemblage. Its relative contribution to biomass and the environmental factors that may regulate picoplankton were also investigated. Our results revealed great stability in temporal dynamic of picoplankton in a seasonal scale, despite considerable interannual variation related to El Niño (ENSO) event in 2015. Heterotrophic bacteria dominated picoplankton during the entire study period. Autotrophic picoplankton (Synechococcus + picoeukaryotes) contributed in average for 30% of total picoplankton biomass, and for 58% of total chlorophyll a. Salinity proved to be the best predictor of picoplankton, with greater abundances during periods of low salinity. However, weak environmental relationships founded may suggest a greater importance of biological interactions (as competition and/or grazing) leading to picoplankton fluctuations. This evidence provides a new perspective that picoplankton may exhibit more pronounced fluctuations in interannual intervals in the tropical region, but it is of permanent relevance for C cycling, especially in a climate change scenario.