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1. Multifaceted impacts of the stony coral Porites astreoides on picoplankton abundance and community composition: Corals impact reef picoplankton

   https://doi.org/10.1002/lno.10389  

   McNally, Sean P. ; Parsons, Rachel J. ; Santoro, Alyson E. ; Apprill, Amy ( January 2017 , Limnology and Oceanography)
2. Arsenic and Mercury Distribution in an Aquatic Food Chain: Importance of Femtoplankton and Picoplankton Filtration Fractions

   https://doi.org/10.1002/etc.5516  

   Alowaifeer, Abdullah M. ; Clingenpeel, Scott ; Kan, Jinjun ; Bigelow, Patricia E. ; Yoshinaga, Masafumi ; Bothner, Brian ; McDermott, Timothy R. ( December 2022 , Environmental Toxicology and Chemistry)

   Arsenic (As) and mercury (Hg) were examined in the Yellowstone Lake food chain, focusing on two lake locations separated by approximately 20 km and differing in lake floor hydrothermal vent activity. Sampling spanned from femtoplankton to the main fish species, Yellowstone cutthroat trout and the apex predator lake trout. Mercury bioaccumulated in muscle and liver of both trout species, biomagnifying with age, whereas As decreased in older fish, which indicates differential exposure routes for these metal(loid)s. Mercury and As concentrations were higher in all food chain filter fractions (0.1‐, 0.8‐, and 3.0‐μm filters) at the vent‐associated Inflated Plain site, illustrating the impact of localized hydrothermal inputs. Femtoplankton and picoplankton size biomass (0.1‐ and 0.8‐μm filters) accounted for 30%–70% of total Hg or As at both locations. By contrast, only approximately 4% of As and <1% of Hg were found in the 0.1‐μm filtrate, indicating that comparatively little As or Hg actually exists as an ionic form or intercalated with humic compounds, a frequent assumption in freshwaters and marine waters. Ribosomal RNA (18S) gene sequencing of DNA derived from the 0.1‐, 0.8‐, and 3.0‐μm filters showed significant eukaryote biomass in these fractions, providing a novel view of the femtoplankton and picoplankton size biomass, which assists in explaining why these fractions may contain such significant Hg and As. These results infer that femtoplankton and picoplankton metal(loid) loads represent aquatic food chain entry points that need to be accounted for and that are important for better understanding Hg and As biochemistry in aquatic systems.Environ Toxicol Chem2023;42:225–241. © 2022 SETAC

    

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3. Dynamic marine viral infections and major contribution to photosynthetic processes shown by spatiotemporal picoplankton metatranscriptomes

   https://doi.org/10.1038/s41467-019-09106-z  

   Sieradzki, Ella T. ; Ignacio-Espinoza, J. Cesar ; Needham, David M. ; Fichot, Erin B. ; Fuhrman, Jed A. ( December 2019 , Nature Communications)
4. Coexisting picoplankton experience different relative grazing pressures across an ocean productivity gradient

   https://doi.org/10.1073/pnas.2220771120  

   Landry, Michael R. ; Stukel, Michael R. ; Selph, Karen E. ; Goericke, Ralf ( October 2023 , Proceedings of the National Academy of Sciences)

   Picophytoplankton populations [Prochlorococcus,Synechococcus(SYN), and picoeukaryotes] are dominant primary producers in the open ocean and projected to become more important with climate change. Their fates can vary, however, with microbial food web complexities. In the California Current Ecosystem, picophytoplankton biomass and abundance peak in waters of intermediate productivity and decrease at higher production. Using experimental data from eight cruises crossing the pronounced CCE trophic gradient, we tested the hypothesis that these declines are driven by intensified grazing on heterotrophic bacteria (HBAC) passed to similarly sized picophytoplankton via shared predators. Results confirm previously observed distributions as well as significant increases in bacterial abundance, cell growth, and grazing mortality with primary production. Mortalities of picophytoplankton, however, diverge from the bacterial mortality trend such that relative grazing rates on SYN compared to HBAC decline by 12-fold between low and high productivity waters. The large shifts in mortality rate ratios for coexisting populations are not explained by size variability but rather suggest high selectivity of grazer assemblages or tightly coupled tradeoffs in microbial growth advantages and grazing vulnerabilities. These findings challenge the long-held view that protistan grazing mainly determines overall biomass of microbial communities while viruses uniquely regulate diversity by “killing the winners”.

    

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5. Size dependence of metabolism within marine picoplankton populations

   https://doi.org/10.1002/lno.11153  

   Casey, John R. ; Björkman, Karin M. ; Ferrón, Sara ; Karl, David M. ( February 2019 , Limnology and Oceanography)

   Cell size is broadly applied as a convenient parameterization of ecosystem models and is widely applicable to constrain the activities of organisms spanning large size ranges. However, the size structure of the majority of the marine picoplankton assemblage is narrow and beneath the lower size limit of the empirical allometric relationships established so far (typically >1 μm). We applied a fine‐resolution (0.05 μm increments) size fractionation method to estimate the size dependence of metabolic activities of picoplankton populations in the 0.10–1.00 μm size interval within the surface North Pacific Subtropical Gyre microbial assemblage. Group‐specific carbon retained on each filter was quantified by flow cytometric conversion of light scatter to cellular carbon quotas. Median carbon quotas were 25.7, 22.6, and 5.9 fg C cell⁻¹for populations of the picocyanobacteriumProchlorococcus, high‐scatter heterotrophs, and low‐scatter heterotrophs, respectively. Carbon‐specific rates of primary production as a function of cell size, using the¹⁴C method, and phosphate transport, using³³P radiotracers, resulted in negative power scalings (b) within populations ofProchlorococcusand heterotrophs ofb = −1.3 andb = −1.1, respectively. These findings are in contrast to the positive empirical power scaling comprising the broader and larger prokaryote category (b = 0.7) and point to within‐population variability in cell physiology and metabolism for these important microbial groups.

    

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