Cellular carbon and nitrogen content and cell volume of nutritionally and morphologically diverse dinoflagellate species were measured to determine carbon to volume (C : vol) and nitrogen to volume (N : vol) relationships. Cellular C and N content ranged from 48 to 3.0 ϫ 10 4 pgC cell Ϫ1 and 11 to 2,656 pgN cell Ϫ1 for cells ranging in volume from 180 to 2.8 ϫ 10 5 m 3 . C and N density in dinoflagellates decreased significantly with increasing cell volume. C : N ratios ranged from 3.44 to 6.45. C : vol and N : vol in dinoflagellates are significantly related as expressed by the equations pgC cell Ϫ1 ϭ 0.760 ϫ volume 0.819 and pgN cell Ϫ1 ϭ 0.118 ϫ volume 0.849 . Previously published data were combined to compare C : vol relationships in different phylogenetic protist groups, including chlorophytes, chrysophytes, prasinophytes, and prymnesiophytes. Our analysis indicated differences between the C : vol relationships available for ciliates. A new C : vol relationship for diatoms was established (pgC cell Ϫ1 ϭ 0.288 ϫ volume 0.811 ). Dinoflagellates are significantly more C dense than diatoms. Except for diatoms, we found few significant differences between C : vol relationships of different phylogenetic groups. Consequently, one C : vol relationship for taxonomically diverse protist plankton excluding diatoms was determined (pgC cell Ϫ1 ϭ 0.216 ϫ volume 0.939 ). In the combined data set, carbon density was not constant but decreased significantly with increasing cell volume. Using constant C : vol conversion factors for plankton over large size ranges will cause systematic errors in biomass estimates.

Current sampling of genomic sequence data from eukaryotes is relatively poor, biased, and inadequate to address important questions about their biology, evolution, and ecology; this Community Page describes a resource of 700 transcriptomes from marine microbial eukaryotes to help understand their role in the world's oceans.

New sequences of ribosomal and protein genes were combined with available morphological and paleontological data to produce a phylogenetic framework for dinoflagellates. The evolutionary history of some of the major morphological features of the group was then investigated in the light of that framework. Phylogenetic trees of dinoflagellates based on the small subunit ribosomal RNA gene (SSU) are generally poorly resolved but include many wellsupported clades, and while combined analyses of SSU and LSU (large subunit ribosomal RNA) improve the support for several nodes, they are still generally unsatisfactory. Protein-gene based trees lack the degree of species representation necessary for meaningful in-group phylogenetic analyses, but do provide important insights to the phylogenetic position of dinoflagellates as a whole and on the identity of their close relatives. Molecular data agree with paleontology in suggesting an early evolutionary radiation of the group, but whereas paleontological data include only taxa with fossilizable cysts, the new data examined here establish that this radiation event included all dinokaryotic lineages, including athecate forms. Plastids were lost and replaced many times in dinoflagellates, a situation entirely unique for this group. Histones could well have been lost earlier in the lineage than previously assumed. The closest relatives to the dinokaryotic dinoflagellates appear to be apicomplexans, Perkinsus and Parvilucifera, syndinians and Oxyrrhis. Gonyaulacales, Dinophysiales and an expanded Suessiales are all holophyletic orders, while Gymnodiniales, Blastodiniales and Phytodiniales as currently circumscribed are polyphyletic. Peridiniales is likely to be a paraphyletic taxon that probably gave rise to Dinophysiales and Prorocentrales, as well as to several groups of Gymnodiniales and Blastodiniales, and possibly also to Gonyaulacales.

The North Atlantic Aerosols and Marine Ecosystems Study (NAAMES) is an interdisciplinary investigation to improve understanding of Earth's ocean ecosystem-aerosol-cloud system. Specific overarching science objectives for NAAMES are to (1) characterize plankton ecosystem properties during primary phases of the annual cycle and their dependence on environmental forcings, (2) determine how these phases interact to recreate each year the conditions for an annual plankton bloom, and (3) resolve how remote marine aerosols and boundary layer clouds are influenced by plankton ecosystems. Four NAAMES field campaigns were conducted in the western subarctic Atlantic between November 2015 and April 2018, with each campaign targeting specific Behrenfeld et al. NAAMES Overview seasonal events in the annual plankton cycle. A broad diversity of measurements were collected during each campaign, including ship, aircraft, autonomous float and drifter, and satellite observations. Here, we present an overview of NAAMES science motives, experimental design, and measurements. We then briefly describe conditions and accomplishments during each of the four field campaigns and provide information on how to access NAAMES data. The intent of this manuscript is to familiarize the broad scientific community with NAAMES and to provide a common reference overview of the project for upcoming publications.

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.

Rates of heterotrophic protist grazing and phytoplankton growth were measured weekly to biweekly in Narragansett Bay, Rhode Island, USA, from January 2010 to February 2011. In situ sensor data and species composition were collected concomitantly to link patterns in plankton dynamics with ancillary environmental and biological processes. Annual average phytoplankton growth rates were 0.69 ± 0.58 d −1 , and heterotrophic protist grazing rates were 0.79 ± 0.61 d −1. Phytoplankton growth rates were at times negative in both winter and spring. Nutrient limitation was only detected during summer, and negative growth rates in winter did not result from nutrient limitation. On an annual average, grazing removed 96% (20 to 200%) of primary production, with peaks in both phytoplankton growth and heterotrophic protist grazing rates during summer. There was no relationship between protistan herbivory rates and initial chlorophyll a concentration. Dominant grazer taxa changed seasonally. Heterotrophic dinoflagellates dominated in summer and were associated with significantly higher than average grazing rates (>1 d −1). Seasonal changes in grazing rates were most significantly characterized by seasonal changes in both temperature and plankton community composition. The relative effects of temperature and species composition could not be distinguished statistically. The magnitude of protistan grazing and subsequent effects on trophic transfer and primary production rates as well as phytoplankton community composition may be better understood and parameterized when grazing pressure is evaluated in relation to species composition and environmental conditions rather than bulk measures of biomass.

Plankton biomass estimates are often made using cell size measurements from samples preserved with fixatives such as Lugol's or glutaraldehyde. However, preservation of plankton samples can introduce artifacts to species abundance and cell volume estimates. The goal of this study was to quantify the extent of fixation-induced cell volume change in 18 species of dinoflagellates and 8 species of diatoms in order to provide correction factors to improve biomass estimates. Highly variable and species-specific cell volume changes were found with respect to cell covering, fixative type and strength, time of storage and analysis method (light vs epifluorescence microscopy). Both swelling and shrinking were observed with both fixatives in dinoflagellates and diatoms. Dinoflagellate cell volume changes ranged from over 60% shrinkage to 30% swelling. Cell volume of some diatom species shrank over 30% and swelled almost 30%. These results contradict the common assumption that diatoms are not affected by preservation due to their silica frustule. The observed cell volume changes for both dinoflagellates and diatoms differed from those reported for ciliates and other flagellates. Therefore, application of previously reported correction factors would lead to inaccurate estimates of biovolume and thus carbon biomass. Fixation caused significant changes in biomass predictions of individual dinoflagellate and diatom species. However, biomass estimates for samples containing several species were not significantly different whether based on live or fixed cell volumes.

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