Small pigmented eukaryote assemblages of the western tropical North Atlantic around the Amazon River plume during spring discharge

Abstract

Small pigmented eukaryotes (⩽ 5 µm) are an important, but overlooked component of global marine phytoplankton. The Amazon River plume delivers nutrients into the oligotrophic western tropical North Atlantic, shades the deeper waters, and drives the structure of microphytoplankton (> 20 µm) communities. For small pigmented eukaryotes, however, diversity and distribution in the region remain unknown, despite their significant contribution to open ocean primary production and other biogeochemical processes. To investigate how habitats created by the Amazon river plume shape small pigmented eukaryote communities, we used high-throughput sequencing of the 18S ribosomal RNA genes from up to five distinct small pigmented eukaryote cell populations, identified and sorted by flow cytometry. Small pigmented eukaryotes dominated small phytoplankton biomass across all habitat types, but the population abundances varied among stations resulting in a random distribution. Small pigmented eukaryote communities were consistently dominated by Chloropicophyceae (0.8–2 µm) and Bacillariophyceae (0.8–3.5 µm), accompanied by MOCH-5 at the surface or by Dinophyceae at the chlorophyll maximum. Taxonomic composition only displayed differences in the old plume core and at one of the plume margin stations. Such results reflect the dynamic interactions of the plume and offshore oceanic waters and suggest that the resident small pigmented eukaryote diversity was not strongly affected by habitat types at this time of the year.

Responses of Phytoplankton Communities to the Effect of Both River Plume and Coastal Upwelling

“…These traits likely account for their dominance in the nutrient‐rich, upwelled waters of this study. This pattern is consistent with observations in other upwelling regions (Charvet et al., 2021; Cheung et al., 2021; Weber et al., 2019; Zhou et al., 2019). The diatom biomass as well as the TChl a was lower in the plume than in the upwelled water because consumption of both DIP and DIN decreased as the plume extended (Figures 2b and 2d and Figures 5a and 5b).…”

The Spatial Variation in Chlorophyte Community Composition From Coastal to Offshore Waters in a Subtropical Continental Shelf System

“…Since chlorophytes seldom uptake silicate directly, their diversity and communities might be influenced by the diatom. The pico-and nano-sized diatoms have been found to be important in many marine systems recently (Leblanc et al, 2018;Charvet et al, 2021), including in this study (Figure S5), and they might compete with the chlorophyte communities due to their similar size range. On the other hand, there may be other factors which covary with silicate concentration, e.g., turbidity.…”

“…Thus, ASV is better than OTU at representing the taxonomic groups for chlorophytes. The distribution patterns of certain chlorophyte groups have already been demonstrated, for example that Mamiellophyceae is dominant in coastal water whereas Chloropicophyceae and prasinophytes clade IX are dominant in oceanic waters as well as in tropical regions (Tragin et al, 2016;Dos Santos et al, 2017a;Charvet et al, 2021). This study conducted grid sampling at surface and DCM layers on the continental shelf region to provide a high-resolution examination of chlorophyte community variation.…”

Opportunistic sightings of manta rays on Brazil's Amazon Coast

“…The BAC is greatly influenced by the Amazon River discharge and plume, with strong salinity gradients, inorganic nutrients, and turbidity (Charvet et al, 2021). The hydrodynamic conditions of the estuaries change dramatically during every tidal cycle, affecting water stratification, saltwater intrusion, sediment transport, turbidity, as well as light and nutrient distribution (Nwe et al, 2022).…”