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Here we described the general hydrography in the South Brazil Bight (23–28°S) with emphasis on frontal processes and their role in the structure and functioning of the regional shelf ecosystem. One of the key roles of fronts for ecosystem dynamics is the injection of nutrients into the euphotic zone increasing primary production. Frontal systems also affect plankton biodiversity and fisheries. Physical mechanisms behind frontogenesis in this region are similar in the analogous western side of oceanic basins; their magnitude and seasonal dynamics, however, may differ due to peculiarities in shelf morphology, wind field, tidal circulation and continental drainage. Here we provide a reassessment of earlier and recent ecological and hydrographic studies for a better evaluation of the spatial and temporal dynamics of fronts and their regional ecological implications. Albeit in a fragmented manner, we give a more detailed conceptual framework about the ecosystem responses to the complex frontal system in the South Brazil Bight. [ABSTRACT FROM AUTHOR]

Five oceanographic cruises were made between November 2005 and June 2006, sampling a cross-shelf transect off the South Brazilian Bight (SBB; 26°46′S) to follow the seasonal development of the South Atlantic Central Water (SACW) intrusion over the shelf and its influence on the assemblage of planktonic cnidarians. An onshore wind-driven bottom intrusion of the SACW was clearly perceptible, reaching the coast in January. From March onward, the SACW influence was gradually displaced seaward due to wind and tidal mixing. By late June the SACW influence was offshore and the inshore was dominated by low-salinity waters (<34.5). The abundance, distribution, and general taxonomic composition of both medusae and siphonophores were strongly influenced by the onshore intrusion of the SACW. An inshore–offshore gradient was clear. The Canonical Correspondence Analysis suggested that coastal species – dominated by Liriope tetraphylla , actinula larvae and Muggiaea kochi – were mostly related to food availability and a vertically mixed environment inshore, and their abundance and extent were reduced during intrusion periods. In contrast, species with offshore affinities tended to increase their abundance and distribution during intrusion periods, and were mostly related to the presence of thermal stratification and a deep chlorophyll maximum layer. Most of these offshore species, such as Aglaura hemistoma , Rhopalonema velatum and many calycophorans, are associated with the warm upper layer. However, high concentrations of large (>20 mm in diameter) Solmaris corona were observed exclusively in cold waters, suggesting this medusa is a SACW indicator. [ABSTRACT FROM AUTHOR]

• Rio Grande Rise pelagic microbiome. • Picoplankton abundance. • Dominance of heterotrophic bacteria. Marine microbes control the flux of matter and energy essential for life in the oceans. Until now, the distribution and diversity of planktonic microorganisms above Fe-Mn crusts have received relatively little attention. Future deep-sea mining is predicted to affect microbial diversity. Here, we studied the ecology of picoplankton among pelagic zones of a Fe-Mn deposit region, at Rio Grande Rise, Southwestern Atlantic Ocean. We investigated microbial community composition using high-throughput sequencing of 16S rRNA genes and their abundance estimated by flow cytometry. The picoplankton populations were more abundant in epi- and mesopelagic waters, corresponding to the Tropical and South Atlantic Central Water masses. Bacterial groups related to heterotrophy, such as Oceanospirillales (Gammapoteobacteria), SAR11 (Alphapoteobacteria), Flavobacteriales (Bacteroida), and Rhodobacterales (Alphapoteobacteria), were the main representatives of the pelagic microbial community. Additionally, we detected abundant assemblages belonging to acetate-oxidizing manganese reducers, i.e., Alteromona s. No differences were observed in microbial community diversity among pelagic zones and water masses. These results provide the first insights into the picoplankton abundance, taxonomy and diversity, and ecological processes in the Rio Grande Rise of the Atlantic Ocean. This may also support draft regulations for deep-sea mining in the region. [ABSTRACT FROM AUTHOR]