The rapid increase in the volume and variety of terrestrial biosphere observations (i.e., remote sensing data and in situ measurements) offers a unique opportunity to derive ecological insights, refine process‐based models, and improve forecasting for decision support. However, despite their potential, ecological observations have primarily been used to benchmark process‐based models, as many past and current models lack the c...

Marine eastern boundary current ecosystems, such as the California Current System (CCS), involve productive, mesotrophic transition zones. The CCS exhibits highly variable primary production (PP), yet factors driving the variability and underlying phytoplankton communities remain poorly understood. We integrated physicochemical and biological data from surface waters sampled during 10 CCS expeditions, spanning 13 yr, and resol...

While droughts predominantly induce immediate reductions in plant carbon uptake, they can also exert long‐lasting effects on carbon fluxes through associated changes in leaf area, soil carbon, etc. Among other mechanisms, shifts in carbon allocation due to water stress can contribute to the legacy effects of drought on carbon fluxes. However, the magnitude and impact of these allocation shifts on carbon fluxes and pools remain...

The Bay of Bengal (BoB) spans >2.2 million km 2 in the northeastern Indian Ocean and is bordered by dense populations that depend upon its resources. Over recent decades, a shift from larger phytoplankton to picoplankton has been reported, yet the abundance, activity, and composition of primary producer communities are not well‐characterized. We analysed the BoB regions during the summer monsoon. Prochlorococcus ranged up to 3...

Microbial communities are commonly characterised through the metabarcoding of environmental DNA. This DNA originates from both viable (including dormant and active) and dead organisms, leading to recent efforts to distinguish between these states. In this study, we further these approaches by distinguishing not only between viable and dead cells but also between dormant and actively growing cells. This is achieved by sequencin...

The Bay of Bengal (BoB) is a 2,600,000 km 2 expanse in the Indian Ocean upon which many humans rely. However, the primary producers underpinning food chains here remain poorly characterized. We examined phytoplankton abundance and diversity along strong BoB latitudinal and vertical salinity gradients—which have low temperature variation (27–29°C) between the surface and subsurface chlorophyll maximum (SCM). In surface waters,...

Tropical environments with unique abiotic and biotic factors—such as salt ponds, mangroves, and coral reefs—are often in close proximity. The heterogeneity of these environments is reflected in community shifts over short distances, resulting in high biodiversity. While phytoplankton assemblages physically associated with corals, particularly their symbionts, are well studied, less is known about phytoplankton diversity across...

Accurate estimation and forecasts of net biome CO 2 exchange (NBE) are vital for understanding the role of terrestrial ecosystems in a changing climate. Prior efforts to improve NBE predictions have predominantly focused on increasing models' structural realism (and thus complexity), but parametric error and uncertainty are also key determinants of model skill. Here, we investigate how different parameterization assumptions pr...

Planktonic communities constitute the basis of life in marine environments and have profound impacts in geochemical cycles. In the North Atlantic, seasonality drives annual transitions in the ecology of the water column. Phytoplankton bloom annually in spring as a result of these transitions, creating one of the major biological pulses in productivity on earth. The timing and geographical distribution of the spring bloom as we...

Vitamin B1 (thiamin) is an essential coenzyme for all cells. Recent findings from experimental cell biology and genome surveys have shown that thiamin cycling by plankton is far more complex than was previously understood. Many plankton cells cannot produce thiamin (are auxotrophic) and obligately require an exogenous source of thiamin or one or more of 5 different thiamin-related compounds (TRCs). Despite this emerging eviden...

Summary In marine ecosystems, viruses are major disrupters of the direct flow of carbon and nutrients to higher trophic levels. Although the genetic diversity of several eukaryotic phytoplankton virus groups has been characterized, their infection dynamics are less understood, such that the physiological and ecological implications of their diversity remain unclear. We compared genomes and infection phenotypes of the two most...

Summary Prasinophytes are widespread marine algae for which responses to nutrient limitation and viral infection are not well understood. We studied the picoprasinophyte, Micromonas pusilla , grown under phosphate‐replete (0.65 ± 0.07 d −1 ) and 10‐fold lower (low)‐phosphate (0.11 ± 0.04 d −1 ) conditions, and infected by the phycodnavirus MpV‐SP1. Expression of 17% of Micromonas genes in uninfected cells differed by >1.5‐fold...

Summary Photosynthetic picoeukaryotes contribute a significant fraction of primary production in the upper ocean. Micromonas pusilla is an ecologically relevant photosynthetic picoeukaryote, abundantly and widely distributed in marine waters. Grazing by protists may control the abundance of picoeukaryotes such as M. pusilla , but the diversity of the responsible grazers is poorly understood. To identify protists consuming phot...

Summary Bathycoccus and Ostreococcus are broadly distributed marine picoprasinophyte algae. We enumerated small phytoplankton using flow cytometry and qPCR assays for phylogenetically distinct Bathycoccus clades BI and BII and Ostreococcus clades OI and OII. Among 259 photic‐zone samples from transects and time‐series, Ostreococcus maxima occurred in the North Pacific coastal upwelling for OI (36 713 ± 1485 copies ml −1 ) and...

Western boundary currents support high primary production and carbon export. Here, we performed a survey of photosynthetic picoeukaryotes in the North Pacific Ocean in four transects crossing the Kuroshio Front. Prasinophyte algae comprised 85% of 18S rRNA gene sequences for photosynthetic taxa in the Micromonas and Ostreococcus comprised 30% and 51% of the total photosynthetic 18S rDNA sequences from five stations. Phylogenet...

Summary The cyanobacteria P rochlorococcus and S ynechococcus are important marine primary producers. We explored their distributions and covariance along a physico‐chemical gradient from coastal to open ocean waters in the N ortheastern P acific O cean. An inter‐annual pattern was delineated in the dynamic transition zone where upwelled and eastern boundary current waters mix, and two new S ynechococcus clades, Eastern Pacifi...

Summary Phosphate (PO 4 ) is an important limiting nutrient in marine environments. Marine cyanobacteria scavenge PO 4 using the high‐affinity periplasmic phosphate binding protein PstS. The pstS gene has recently been identified in genomes of cyanobacterial viruses as well. Here, we analyse genes encoding transporters in genomes from viruses that infect eukaryotic phytoplankton. We identified inorganic PO 4 transporter‐encodi...

Summary Unicellular eukaryotes (protists) are key components of marine food webs, yet knowledge of their diversity, distributions and respective ecologies is limited. We investigated uncultured protists using 18S rRNA gene sequencing, phylogenetic analyses, specific fluorescence in situ hybridization (FISH) probes and other methods. Because few studies have been conducted in warm water systems, we focused on two Atlantic subtr...

Summary Eukaryotic molecular diversity within the picoplanktonic size‐fraction has primarily been studied in marine surface waters. Here, the vertical distribution of picoeukaryotic diversity was investigated in the Sargasso Sea from euphotic to abyssal waters, using size‐fractionated samples ( N ovel A lveolate groups I and II (NAI and NAII), or the novel Ma rine St ramenopiles (MAST). However, some deep‐sea NAII formed disti...

Summary Cholera disease, caused by the bacterium Vibrio cholerae , afflicts hundreds of thousands worldwide each year. Endemic to aquatic environments, V. cholerae 's proliferation and dynamics in marine systems are not well understood. Here, we show that under a variety of coastal seawater conditions V. cholerae remained primarily in a free‐living state as opposed to attaching to particles. Growth rates of free‐living V. chol...

We assess population dynamics of picophytoplankton groups (≤2 µm diameter; Prochlorococcus , Synechococcus, and picoeukaryote) at a Pacific Ocean coastal site in the Southern California Bight. Weekly sampling (August 2000 to January 2002), dilution experiments, and flow cytometric analysis were combined with an instrument‐specific calibration for cell size determination, allowing biovolume and carbon biomass estimation. Synech...