Abundance and Microbial Diversity from Surface to Deep Water Layers Over the Rio Grande Rise, South Atlantic

Abstract

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 has received relatively little attention. Future mining\dredging of these minerals is predicted to affect microbial diversity and functioning in the deep sea. Here, we studied the ecology of planktonic microbes among pelagic environments of an 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. Our results showed that the majority of picoplanktonic was found in epi- and mesopelagic waters, corresponding to the Tropical Water and South Atlantic Central Water. Bacterial and archaeal groups related to phototrophy, heterotrophy and chemosynthesis, such as Synechococcales, Sar11 (Proteobacteria) and Nitrosopumilales (Thaumarchaeota) were the main representatives of the pelagic microbial community. Additionally, we detected abundant assemblages involved in biodegradation of marine organic matter and iron oxidation at deep waters, i.e., Pseudoalteromonas and Alteromonas. No differences were observed in microbial community alpha diversity. However, we detected differences in community structure between water masses, suggesting that changes in an environmental setting (i.e. nutrient availability or circulation) play a significant role in structuring the pelagic zones, also affecting the meso- and bathypelagic microbiome.HighlightsRio Grande Rise pelagic microbiomePicoplankton carbon biomass partitioning through pelagic zonesUnique SAR11 Clade I oligotype in the shallowest Tropical WaterHigher number of shared oligotypes between deepest water massesNitrogen, carbon and sulfur may be important contributors for the pelagic microbiome

Metagenomic analyses reveal the influence of depth layers on marine biodiversity in tropical and subtropical regions

“…Bacteria are predominant in the majority of samples. Many factors contribute to the prokaryote diversity in ocean habitats, such as the availability of organic components and particulate matter, pelagic zones, and depth (Mestre et al, 2017; Ferreira et al, 2022; Walsh et al, 2016). In situ studies of deep-sea bacterioplankton showed the occurrence of bacterioplankton control by seafloor virioplankton, as there was a decrease in bacterial diversity and a change in its structure in the presence of diluted viruses (Zhang et al, 2020).…”

Benthic megafauna habitats, community structure and environmental drivers at Rio Grande Rise (SW Atlantic)

“…Water masses are known to have a significant influence on the distribution and composition of coral communities in the Southeast Brazilian continental slope (Arantes et al, 2009;Cavalcanti et al, 2017;Sumida et al, 2004), due to their distinct properties in the water column (temperature, salinity, oxygen, nutrients). In addition, microbial communities from pelagic zones in RGR are structured by water masses (Ferreira et al, 2021). Studies had shown that hexactinellids have high assimilation-to-respiration efficiency for bacteria (Bart et al, 2020), and they are an important functional group that links the pelagic microbial food web to the benthos (Pile and Young, 2006).…”

“…Despite these similarities, closed circulations above seamounts and internal wave formation may act to trap or provide a mechanism for the downward transport of phytoplankton and particulate organic carbon (POC) (Read and Pollard, 2017;Turnewitsch et al, 2016;Vilas et al, 2009;White et al, 2007). However, RGR is in the oligotrophic South Atlantic Gyre, with a low concentration of organic carbon (Perez et al, 2012) and the main reservoir of new nutrients is trapped below the permanent thermocline, in the South Atlantic Central Water (Ferreira et al, 2021). Physical processes induced by RGR and their biological consequences are unknown and should be investigated in future studies to ascertain which processes are related to the ones driven by seamounts.…”

Benthic fauna of the Rio Grande Rise, SW Atlantic: ecology and implications for conservation

“…Water (Ferreira et al, 2021). Physical processes induced by RGR and their biological consequences are unknown and should be investigated in future studies to ascertain which processes are related to the ones driven by seamounts.…”