Small phytoplankton dominate western North Atlantic biomass

Abstract

The North Atlantic phytoplankton spring bloom is the pinnacle in an annual cycle that is driven by physical, chemical, and biological seasonality. Despite its important contributions to the global carbon cycle, transitions in plankton community composition between the winter and spring have been scarcely examined in the North Atlantic. Phytoplankton composition in early winter was compared with latitudinal transects that captured the subsequent spring bloom climax. Amplicon sequence variants (ASVs), imaging flow cytometry, and flow-cytometry provided a synoptic view of phytoplankton diversity. Phytoplankton communities were not uniform across the sites studied, but rather mapped with apparent fidelity onto subpolar-and subtropical-influenced water masses of the North Atlantic. At most stations, cells < 20µm diameter were the main contributors to phytoplankton biomass. Winter phytoplankton communities were dominated by cyanobacteria and pico-phytoeukaryotes. These transitioned to more diverse and dynamic spring communities in which picoand nano-phytoeukaryotes, including many prasinophyte algae, dominated. Diatoms, which are often assumed to be the dominant phytoplankton in blooms, were contributors but not the major component of biomass. We show that diverse, small phytoplankton taxa are unexpectedly common in the western North Atlantic and that regional influences play a large role in modulating community transitions during the seasonal progression of blooms.

The Importance of the Phytoplankton “Middle Class” to Ocean Net Community Production

“…emerging body of observational data (Bolaños et al, 2020;Fowler et al, 2020) suggest that the relationship between the PSD and production is more complex than previously thought. Both bottom-up and top-down processes, including regionally varying supply of limiting nutrients and differential grazing pressure relative to growth, are likely modes of controlling the size fractionation of the phytoplankton communities.…”

Exploring Vitamin B1 Cycling and Its Connections to the Microbial Community in the North Atlantic Ocean

“…Amplification of the V1-V2 region of the 16S rRNA gene was performed using the 27F (5 ′ -AGAGTTTGATCNTGGCTCAG-3) and 338 RPL (5 ′ -GCWGCCWCCCGTAGGWGT-3 ′ ) primers attached to their respective Illumina overhang adapters (Vergin et al, 2013;Illumina Inc.). Polymerase Chain Reactions (PCR) conditions and library construction were done following the NAAMES amplicon protocol as described by Bolaños et al (2020b). Sequencing using the Illumina MiSeq platform (reagent kit v.2; 2X250 Paired-End; Illumina Inc.) was conducted at the Center for Genome Research and Biocomputing at Oregon State University as described previously (Bolaños et al, 2020a,b).…”

“…Trimmed fastq files were quality filtered, dereplicated and merged with dada2 R package, version 1.2 (Callahan et al, 2016). An Amplicon Sequence Variant (ASV) table was constructed as in Bolaños et al (2020b). Taxonomic assignment of the ASVs was determined using a two-step approach (Bolaños et al, 2020b).…”

Multi-Instrument Assessment of Phytoplankton Abundance and Cell Sizes in Mono-Specific Laboratory Cultures and Whole Plankton Community Composition in the North Atlantic

“…While the particles captured by the FlowCam fall within a limited range of the entire size spectrum, imaging of single cells provides a valuable layer of taxonomic information in combination with cell size. By shedding light on the identity of species, particle imaging can expand information gained from molecular analyses of species diversity, where taxonomic resolution is often limited to the class level (e.g., Bolaños et al, 2020). This is exemplified at S3 (Figure 6), where images show that both coccolithophores and the colonial species Corymbellus aureus likely contributed to the molecularly detected Prymnesiophyceae (Bolaños et al, 2020).…”