title: Pico and nanoplankton abundance and carbon stocks along the Brazilian Bight.
abstract: Pico and nanoplankton communities from the Southwest Atlantic Ocean along the Brazilian Bight are poorly described. The hydrography in this region is dominated by a complex system of layered water masses, which includes the warm and oligotrophic Tropical Water (TW), the cold and nutrient rich South Atlantic Central Water (SACW) and the Coastal Water (CW), which have highly variable properties. In order to assess how pico- and nanoplankton communities are distributed in these different water masses, we determined by flow cytometry the abundance of heterotrophic bacteria,Prochlorococcus,Synechococcusand autotrophic pico and nanoeukaryotes along three transects, extending from 23°S to 31°S and 39°W to 49°W. Heterotrophic bacteria (including archaea, maximum of 1.5 × 106cells mL-1) were most abundant in Coastal and Tropical Water whereasProchlorococcuswas most abundant in open-ocean oligotrophic waters (maximum of 300 × 103cells mL-1).Synechococcus(up to 81 × 103cells mL-1), as well as autotrophic pico and nanoeukaryotes seemed to benefit from the influx of nutrient-rich waters near the continental slope. Autotrophic pico and nanoeukaryotes were also abundant in deep chlorophyll maximum (DCM) layers from offshore waters, and their highest abundances were 20 × 103cells mL-1and 5 × 103cells mL-1, respectively. These data are consistent with previous observations in other marine areas whereSynechococcusand autotrophic eukaryotes dominate mesotrophic waters, whereasProchlorococcusdominate in more oligotrophic areas. Regardless of the microbial community structure near the surface, the carbon stock dominance by autotrophic picoeukaryotes near the DCM is possibly linked to vertical mixing of oligotrophic surface waters with the nutrient-rich SACW and their tolerance to lower light levels.
authors.affiliation: Departamento de Oceanografia Biológica, Instituto Oceanográfico, Universidade de São Paulo , São Paulo , Brazil.
authors.forename: Catherine
authors.initials: C
authors.lastname: Gérikas Ribeiro
authors.affiliation: Sorbonne Universités, UPMC Université Paris 06, CNRS, UMR 7144 , Station Biologique de Roscoff , France.
authors.forename: Adriana
authors.initials: A
authors.lastname: Lopes Dos Santos
authors.affiliation: Sorbonne Universités, UPMC Université Paris 06, CNRS, UMR 7144 , Station Biologique de Roscoff , France.
authors.forename: Dominique
authors.initials: D
authors.lastname: Marie
authors.affiliation: Departamento de Oceanografia Biológica, Instituto Oceanográfico, Universidade de São Paulo , São Paulo , Brazil.
authors.forename: Vivian
authors.initials: V
authors.lastname: Helena Pellizari
authors.affiliation: Departamento de Oceanografia Biológica, Instituto Oceanográfico, Universidade de São Paulo , São Paulo , Brazil.
authors.forename: Frederico
authors.initials: F
authors.lastname: Pereira Brandini
authors.affiliation: Sorbonne Universités, UPMC Université Paris 06, CNRS, UMR 7144 , Station Biologique de Roscoff , France.
authors.forename: Daniel
authors.initials: D
authors.lastname: Vaulot
keywords: Flow cytometry; Heterotrophic bacteria; Nanoplankton; Picoplankton; Prochlorococcus; Southwest Atlantic Ocean off Brazil; Synechococcus