Abstract
Molecular analysis revealed diel rhythmicity in the metabolic activity of single-celled microbial eukaryotes (protists) within an eddy in the North Pacific Subtropical Gyre (ca. 100 km NE of station ALOHA). Diel trends among different protistan taxonomic groups reflected distinct nutritional capabilities and temporal niche partitioning. Changes in relative metabolic activities among phototrophs corresponded to the light cycle, generally peaking in mid- to late-afternoon. Metabolic activities of protistan taxa with phagotrophic ability were higher at night, relative to daytime, potentially in response to increased availability of picocyanobacterial prey. Tightly correlated Operational Taxonomic Units throughout the diel cycle implicated the existence of parasitic and mutualistic relationships within the microbial eukaryotic community, underscoring the need to define and include these symbiotic interactions in marine food web descriptions. This study provided a new high-resolution view into the ecologically important interactions among primary producers and consumers that mediate the transfer of carbon to higher trophic levels. Characterizations of the temporal dynamics of protistan activities contribute knowledge for predicting how these microorganisms respond to environmental forcing factors.
Highlights
Single-celled microbial eukaryotes fulfill vital ecological roles as primary producers and consumers at and near the base of marine food webs
The 18S ribosomal RNA gene and ribosomal RNA sequence libraries resulted in an average of 196,410 and 162,815 sequences per sample, which clustered into an average of 1,575 and 1,103 Operational Taxonomic Units (OTUs) per sample, respectively (Figure S2)
To normalize across the entire dataset, samples from both ribosomal DNA (rDNA) and ribosomal RNA (rRNA) sequence libraries were randomly subsampled to 77,221 sequences per sample, which left a total of 3,831 OTUs from the combined rDNA and rRNA sequence library
Summary
Single-celled microbial eukaryotes (protists) fulfill vital ecological roles as primary producers and consumers at and near the base of marine food webs. Environmental factors (e.g., lightdark cycling) influence protistan trophic interactions, studies to characterize how protistan biological activity varies or responds to such changes are critical for understanding ecosystem functioning. Microbial cell cycles have been shown to be synchronized with regular light-dark cycling (diel), especially among photoautotrophs. There is still a need for a comprehensive understanding of how taxon-specific functional roles and trophic interactions are shaped by short-term temporal dynamics (i.e., diel periodicity). Diel synchronization of picophytoplankton behavior, such as cell division and growth, are key biological activities affecting organic matter production and the transfer of carbon to higher trophic levels via protistan grazers. Flow cytometric measurements have demonstrated picophytoplankton cell size to typically increase throughout the course of the light period, followed
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