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Mesoscale oceanographic features, including eddies, have the potential to alter productivity and other biogeochemical rates in the ocean. Here, we examine the microbiome of a cyclonic, Gulf Stream frontal eddy, with a distinct origin and environmental parameters compared to surrounding waters, in order to better understand the processes dominating microbial community assembly in the dynamic coastal ocean. Our microbiome-based approach identified the eddy as distinct from the surround Gulf Stream waters. The eddy-associated microbial community occupied a larger area than identified by temperature and salinity alone, increasing the predicted extent of eddy-associated biogeochemical processes. While the eddy formed on the continental shelf, after two weeks both environmental parameters and microbiome composition of the eddy were most similar to the Gulf Stream, suggesting the effect of environmental filtering on community assembly or physical mixing with adjacent Gulf Stream waters. In spite of the potential for eddy-driven upwelling to introduce nutrients and stimulate primary production, eddy surface waters exhibit lower chlorophyll a along with a distinct and less even microbial community, compared to the Gulf Stream. At the population level, the eddy microbiome exhibited differences among the cyanobacteria (e.g. lower Trichodesmium and higher Prochlorococcus) and in the heterotrophic alpha Proteobacteria (e.g. lower relative abundances of specific SAR11 phylotypes) versus the Gulf Stream. However, better delineation of the relative roles of processes driving eddy community assembly will likely require following the eddy and surrounding waters since inception. Additionally, sampling throughout the water column could better clarify the contribution of these mesoscale features to primary production and carbon export in the oceans.

Gronniger JL, Gray PC, Niebergall AK, Johnson ZI and Hunt DE (2023). A Gulf Stream frontal eddy harbors a distinct microbiome compared to adjacent waters. PLOS ONE 18(11): e0293334. DOI:10.1371/journal.pone.0293334

By mid-century, society will need to significantly intensify the output of its food production system while simultaneously reducing that system’s detrimental impacts on climate, land use, freshwater resources, and biodiversity. This will require finding alternatives to carbon emissions-intensive agriculture, which provides the backbone of today’s global food production system. Here, we explore the hypothesis that marine algae-based aquaculture can help close the projected gap in society’s future nutritional demands while simultaneously improving environmental sustainability. Food production from marine algae-based aquaculture has the potential to contribute more than the total global protein demand projected for 2050, which ranges from 263.8 Mt/yr to 286.5 Mt/yr. It also offers important nutritional and environmental sustainability advantages relative to terrestrial agriculture. Marine algae can provide a better source of high-quality nutritional protein, essential amino acids, and other micronutrients relative to terrestrial plants. In addition, because marine algae do not require soil, irrigation, and the open application of fertilizer, their cultivation does not need to compete with agriculture for arable land and freshwater nor does it lead to fertilizer runoff and downstream eutrophication. Furthermore, by reducing agriculture’s demand for arable land and freshwater, marine algae-based aquaculture can reduce the pressure for deforestation, potentially leading to globally significant reductions in carbon emissions and biodiversity loss.

Greene CH, Scott-Buechler CM, Hausner ALP, Johnson ZI, Lei XG, Huntley ME (2022). Transforming the Future of Marine Aquaculture: A Circular Economy Approach. Oceanography 35: 26-34. https://doi.org/10.5670/oceanog.2022.213

Disturbances, here defined as events that directly alter microbial community composition, are commonly studied in host-associated and engineered systems. In spite of global change both altering environmental averages and increasing extreme events, there has been relatively little research into the causes, persistence and population-level impacts of disturbance in the dynamic coastal ocean. Here, we utilize 3 years of observations from a coastal time series to identify disturbances based on the largest week-over-week changes in the microbiome (i.e. identifying disturbance as events that alter the community composition). In general, these microbiome disturbances were not clearly linked to specific environmental factors and responsive taxa largely differed, aside from SAR11, which generally declined. However, several disturbance metagenomes identified increased phage-associated genes, suggesting that unexplained community shifts might be caused by increased mortality. Furthermore, a category 1 hurricane, the only event that would likely be classified a priori as an environmental disturbance, was not an outlier in microbiome composition, but did enhance a bloom in seasonally abundant phytoplankton. Thus, as extreme environmental changes intensify, assumptions of what constitutes a disturbance should be re-examined in the context of ecological history and microbiome responses.

Gronniger JL, Wang Z, Brandt GR, Ward CS, Tsementzi D, Mu H, Gu J, Johnson ZI, Konstantinidis KT, Hunt DE (2022). Rapid changes in coastal ocean microbiomes uncoupled with shifts in environmental variables. Environmental Microbiology DOI: 10.1111/1462-2920.16086

While planktonic microbes play key roles in the coastal oceans, our understanding of heterotrophic microeukaryotes’ ecology, particularly their spatiotemporal patterns, drivers, and functions, remains incomplete. In this study, we focus on a ubiquitous marine fungus-like protistan group, the Labyrinthulomycetes, whose biomass can exceed that of bacterioplankton in coastal oceans but whose ecology is largely unknown. Using quantitative PCR and amplicon sequencing of their 18S rRNA genes, we examine their community variation in repeated five-station transects across the nearshore-to-offshore surface waters of North Carolina, United States. Their total 18S rRNA gene abundance and phylotype richness decrease significantly from the resource-rich nearshore to the oligotrophic offshore waters, but their Pielou’s community evenness appears to increase offshore. Similar to the bacteria and fungi, the Labyrinthulomycete communities are significantly structured by distance from shore, water temperature, and other environmental factors, suggesting potential niche partitioning. Nevertheless, only several Labyrinthulomycete phylotypes, which belong to aplanochytrids, thraustochytrids, or unclassified Labyrinthulomycetes, are prevalent and correlated with cohesive bacterial communities, while more phylotypes are patchy and often co-occur with fungi. Overall, these results complement previous time-series observations that resolve the Labyrinthulomycetes as persistent and short-blooming ecotypes with distinct seasonal preferences, further revealing their partitioning spatial patterns and multifaceted roles in coastal marine microbial food webs.

Xie N, Wang Z, Hunt DE, Johnson ZI, He Y, Wang G (2022). Niche Partitioning of Labyrinthulomycete Protists Across Sharp Coastal Gradients and Their Putative Relationships With Bacteria and Fungi. Frontiers in Microbiology 13. DOI: 10.3389/fmicb.2022.906864

The biological pump plays a vital role in exporting organic particles into the deep ocean for long-term carbon sequestration. However, much remains unknown about some of its key microbial players. In this study, Labyrinthulomycetes protists (LP) were used to understand the significance of heterotrophic microeukaryotes in the transport of particulate organic matter from the surface to the dark ocean. Unlike the sharp vertical decrease of prokaryotic biomass, the LP biomass only slightly decreased with depth and eventually exceeded prokaryotic biomass in the bathypelagic layer. Sequencing identified high diversity of the LP communities with a dominance of Aplanochytrium at all depths. Notably, ASVs that were observed in the surface layer comprised ~20% of ASVs and ~60% of sequences in each of the deeper (including bathypelagic) layers, suggesting potential vertical export of the LP populations to the deep ocean. Further analyses of the vertical patterns of the 50 most abundant ASVs revealed niche partitioning of LP phylotypes in the pelagic ocean, including those that could decompose organic detritus and/or facilitate the formation of fast-sinking particles. Overall, this study presents several lines of evidence that the LP can be an important component of the biological pump through their multiple ecotypes in the pelagic ocean.

Bai M, Xie N, He Y, Li J, Collier JL, Hunt DE, Johnson ZI, Jiao N, Wang G (2022). Vertical community patterns of Labyrinthulomycetes protists reveal their potential importance in the oceanic biological pump. Environ Microbiol 24: 1703-1713. https://doi.org/10.1111/1462-2920.15709

Using a commercially scalable system designed for processing thousands of liters a day, here we evaluated the factors that affected the performance, energy consumption and capital/operating costs of both flocculation-based and filtration-based algal harvesting systems over a 16 month period. Coagulation efficiency was the primary driver of harvest efficiency in the flocculation-based method, while cell lysis was important for the filtration-based method. Culture (algae) age differentially influenced harvest efficiency through changes in cell fragility and stickiness. The average energy consumption of the flocculation-based method was 0.389 kWh/m3, while that for the filtration-based method was 4.343 kWh/m3. The average harvesting cost of the filtration-based method was 5.35 $/m3, while for flocculation-based method it was 4.52 $/m3. The concentration factor of filtration-based and flocculation-based method were 770–1086 and 407–448, respectively. For both harvesting methods, labor costs dominated and ranged from 55.84%–67.94% of total cost. Further system automation is a potential method to lower the harvesting cost. The filtration-based harvesting method could produce a better quality of algal biomass with higher concentration factors and less ash content, but needed more energy input, as compared with a flocculation-based method. This study highlights the importance of algal culture status to successful harvesting, and it also provides insight into developing more efficient harvesting technology with lower energy and capital cost.

Lu Z, Beal CM, Johnson ZI (2022). Comparative performance and technoeconomic analyses of two microalgae harvesting systems evaluated at a commercially relevant scale. Algal Research 64: 102667. https://doi.org/10.1016/j.algal.2022.102667

The database on ocean primary productivity comprises over two decades (1985–2008) of data that the authors have participated in collecting, using the assimilation of inorganic ¹⁴C through photosynthesis, in incubations carried out in situ. The dataset is perhaps unique in that it uses, overwhelmingly, consistent methodology while covering a wide geographic range. Ancillary data are included. Using the database, it is hoped that investigators can test for the relationships among the environmental drivers for ocean productivity, the meaning of the ¹⁴C method in terms of phytoplankton physiology and the dynamics in the water column, and as a resource for further development of productivity algorithms using satellite ocean color imagery.

Marra JF, Barber RT, Barber E, Bidigare RR, Chamberlin WS, Goericke R, Hargreaves BR, Hiscock M, Iturriaga R, Johnson ZI, Kiefer DA, Kinkade C, Knudson C, Lance V, Langdon C, Lee Z-P, Perry MJ, Smith WO, Vaillancourt R, Zoffoli L (2020). A database of ocean primary productivity from the 14C method. Limnology and Oceanography Letters. https://doi.org/10.1002/lol2.10175

A substantial body of research now exists demonstrating sensitivities of marine organisms to ocean acidification (OA) in laboratory settings. However, corresponding in situ observations of marine species or ecosystem changes that can be unequivocally attributed to anthropogenic OA are limited. Challenges remain in detecting and attributing OA effects in nature, in part because multiple environmental changes are co-occurring with OA, all of which have the potential to influence marine ecosystem responses. Furthermore, the change in ocean pH since the industrial revolution is small relative to the natural variability within many systems, making it difficult to detect, and in some cases, has yet to cross physiological thresholds. The small number of studies that clearly document OA impacts in nature cannot be interpreted as a lack of larger-scale attributable impacts at the present time or in the future but highlights the need for innovative research approaches and analyses. We summarize the general findings in four relatively well-studied marine groups (seagrasses, pteropods, oysters, and coral reefs) and integrate overarching themes to highlight the challenges involved in detecting and attributing the effects of OA in natural environments. We then discuss four potential strategies to better evaluate and attribute OA impacts on species and ecosystems. First, we highlight the need for work quantifying the anthropogenic input of CO₂ in coastal and open-ocean waters to understand how this increase in CO₂ interacts with other physical and chemical factors to drive organismal conditions. Second, understanding OA-induced changes in population-level demography, potentially increased sensitivities in certain life stages, and how these effects scale to ecosystem-level processes (e.g. community metabolism) will improve our ability to attribute impacts to OA among co-varying parameters. Third, there is a great need to understand the potential modulation of OA impacts through the interplay of ecology and evolution (eco–evo dynamics). Lastly, further research efforts designed to detect, quantify, and project the effects of OA on marine organisms and ecosystems utilizing a comparative approach with long-term data sets will also provide critical information for informing the management of marine ecosystems.

Doo SS, Kealoha A, Andersson A, Cohen AL, Hicks TL, Johnson ZI, Long MH, McElhany P, Mollica N, Shamberger KEF, Silbiger NJ, Takeshita Y, Busch DS (2020). The challenges of detecting and attributing ocean acidification impacts on marine ecosystems. ICES Journal of Marine Science. https://doi.org/10.1093/icesjms/fsaa094

Coastal acidification in southeastern U.S. estuaries and coastal waters is influenced by biological activity, run-off from the land, and increasing carbon dioxide in the atmosphere. Acidification can negatively impact coastal resources such as shellfish, finfish, and coral reefs, and the communities that rely on them. Organismal responses for species located in the U.S. Southeast document large negative impacts of acidification, especially in larval stages. For example, the toxicity of pesticides increases under acidified conditions and the combination of acidification and low oxygen has profoundly negative influences on genes regulating oxygen consumption. In corals, the rate of calcification decreases with acidification and processes such as wound recovery, reproduction, and recruitment are negatively impacted. Minimizing the changes in global ocean chemistry will ultimately depend on the reduction of carbon dioxide emissions, but adaptation to these changes and mitigation of the local stressors that exacerbate global acidification can be addressed locally. The evolution of our knowledge of acidification, from basic understanding of the problem to the emergence of applied research and monitoring, has been facilitated by the development of regional Coastal Acidification Networks (CANs) across the United States. This synthesis is a product of the Southeast Coastal and Ocean Acidification Network (SOCAN). SOCAN was established to better understand acidification in the coastal waters of the U.S. Southeast and to foster communication among scientists, resource managers, businesses, and governments in the region. Here we review acidification issues in the U.S. Southeast, including the regional mechanisms of acidification and their potential impacts on biological resources and coastal communities. We recommend research and monitoring priorities and discuss the role SOCAN has in advancing acidification research and mitigation of and adaptation to these changes.

Hall ER, Wickes L, Burnett LE, Scott GI, Hernandez D, Yates KK, Barbero L, Reimer JJ, Baalousha M, Mintz J, Cai W-J, Craig JK, DeVoe MR, Fisher WS, Hathaway TK, Jewett EB, Johnson Z, Keener P, Mordecai RS, Noakes S, Phillips C, Sandifer PA, Schnetzer A, Styron J (2020). Acidification in the U.S. Southeast: Causes, Potential Consequences and the Role of the Southeast Ocean and Coastal Acidification Network. Frontiers in Marine Science 7. https://doi.org/10.3389/fmars.2020.00548

Microalgae hold great promise as environmentally sustainable sources of food, animal feed, and fuel. However, large amounts of water are used during microalgae cultivation and this negatively impacts economic viability and environmental sustainability. Reusing cultivation water can reduce the direct impacts of water usage and also reduce nutrient requirements and algal wastewater treatment. However, studies have shown that algae growth in reused water can be compromised, unaffected, or sometimes enhanced compared to controls. This review examines recent studies on water reuse to qualitatively understand these varied effects. Growth inhibitors and stimulators in reused water and their underlying mechanisms are discussed, as well as recent pre-treatment technologies and factors affecting the quality of reused water, such as microalgae taxa, culture conditions, and harvesting methods, are considered. A scheme is proposed for water reuse and harvesting methods based on the desired algal end products. Taking these findings together, here we provide recommendations for further research directions as well as new insights into designing and integrating a cultivation strategy with a harvesting platform to reuse water for more efficient microalgae cultivation.

Lu Z, Loftus S, Sha J, Wang W, Park MS, Zhang X, Johnson ZI, Hu Q (2020). Water reuse for sustainable microalgae cultivation: Current knowledge and future directions. Resources, Conservation and Recycling 161: 104975. https://doi.org/10.1016/j.resconrec.2020.104975

The decarbonization of agriculture faces many challenges and has received a level of attention insufficient to abate the worst effects of climate change and ensure a sustainable bioeconomy. Agricultural emissions are caused both by fossil-intensive fertilizer use and land-use change, which in turn are driven in part by increasing demand for dietary protein. To address this challenge, we present a synergistic system in which organic waste-derived biogas (a mixture of methane and carbon dioxide) is converted to dietary protein and ammonia fertilizer. This system produces low-carbon fertilizer inputs alongside high-quality protein, addressing the primary drivers of agricultural emissions. If the proposed system were implemented across the United States utilizing readily available organic waste from municipal wastewater, landfills, animal manure, and commercial operations, we estimate 30% of dietary protein intake and 127% of ammonia usage could be displaced while reducing land use, water consumption, and greenhouse gas emissions.

Sagues WJ, Assis CA, Hah P, Sanchez DL, Johnson Z, Acharya M, Jameel H, Park S (2019). Decarbonizing Agriculture through the Conversion of Animal Manure to Dietary Protein and Ammonia Fertilizer. Bioresource Technology: 122493. DOI/10.1016/j.biortech.2019.122493

Recent studies have focused on linking marine microbial communities with environmental factors, yet relatively little is known about the drivers of microbial community patterns across the complex gradients from the nearshore to open ocean. Here, we examine microbial dynamics in 15 five‐station transects beginning at the estuarine Piver’s Island Coastal Observatory (PICO) time‐series site and continuing 87 km across the continental shelf to the oligotrophic waters of the Sargasso Sea. 16S rRNA gene libraries reveal strong clustering by sampling site with distinct nearshore, continental shelf, and offshore oceanic communities. Water temperature and distance from shore (which serves as a proxy for gradients in factors such as productivity, terrestrial input, and nutrients) both most influence community composition. However, at the phylotype level, modeling shows the distribution of some taxa is linked to temperature, others to distance from shore and some by both factors, highlighting that taxa with distinct environmental preferences underlie apparent clustering by station. Thus, continental margins contain microbial communities that are distinct from those of either the nearshore or offshore environments and contain mixtures of phylotypes with nearshore or offshore preferences rather than those unique to the shelf environment.

Wang Z, Juarez DL, Pan J-F, Blinebry SK, Gronniger J, Clark JS, Johnson ZI, Hunt DE Microbial communities across nearshore to offshore coastal transects are primarily shaped by distance and temperature. Environ Microbiol. DOI: 10.1111/1462-2920.14734

Reusing growth medium (water supplemented with nutrients) for microalgae cultivation is required for economical and environmentally sustainable production of algae bioproducts (fuels, feed, and food). However, reused medium often contains microbes and dissolved organic matter that may affect algae growth. While the accumulation of dissolved organic carbon (DOC) in reused medium has been demonstrated, it is unclear whether DOC concentrations affect algae growth or subsequent rates of algal DOC release. To address these questions, lab-scale experiments were conducted with three marine microalgae strains, Navicula sp. SFP, Staurosira sp. C323, and Chlorella sp. D046, grown in medium reused up to four times. Navicula sp. and Chlorella sp. grew similarly in reused medium as in fresh medium, while Staurosira sp. became completely inhibited in reused medium. Across the three algae, there was no broad trend between initial DOC concentration in reused medium and algae growth response. Navicula sp. released less DOC overall in reused medium than in fresh medium, but DOC release rates did not decrease proportionally with increased DOC concentrations. Net DOC accumulation was much lower than gross DOC released by Navicula sp. and Staurosira sp., indicating the majority of released DOC was degraded. Additionally, biodegradation experiments with reused media showed no further net decrease in DOC, suggesting the accumulated DOC was recalcitrant to the associated bacteria. Overall, these results suggest that taxa-specific factors may be responsible for algae growth response in reused medium, and that DOC release and accumulation are insensitive to prior cultivation rounds. Choosing an algae strain that is uninhibited by accumulated DOC is therefore critical to ensure successful water reuse in the algae industry.

Loftus SE, Johnson ZI (2019). Reused Cultivation Water Accumulates Dissolved Organic Carbon and Uniquely Influences Different Marine Microalgae. Frontiers in Bioengineering and Biotechnology 7. http://doi.org/10.3389/fbioe.2019.00101

Subsurface chlorophyll maximum layers (SCMLs) are nearly ubiquitous in stratified water columns and exist at horizontal scales ranging from the submesoscale to the extent of oligotrophic gyres. These layers of heightened chlorophyll and/or phytoplankton concentrations are generally thought to be a consequence of a balance between light energy from above and a limiting nutrient flux from below, typically nitrate (NO₃). Here we present multiple lines of evidence demonstrating that iron (Fe) limits or with light colimits phytoplankton communities in SCMLs along a primary productivity gradient from coastal to oligotrophic offshore waters in the southern California Current ecosystem. SCML phytoplankton responded markedly to added Fe or Fe/light in experimental incubations and transcripts of diatom and picoeukaryote Fe stress genes were strikingly abundant in SCML metatranscriptomes. Using a biogeochemical proxy with data from a 40-y time series, we find that diatoms growing in California Current SCMLs are persistently Fe deficient during the spring and summer growing season. We also find that the spatial extent of Fe deficiency within California Current SCMLs has significantly increased over the last 25 y in line with a regional climate index. Finally, we show that diatom Fe deficiency may be common in the subsurface of major upwelling zones worldwide. Our results have important implications for our understanding of the biogeochemical consequences of marine SCML formation and maintenance.

Hogle SL, Dupont CL, Hopkinson BM, King AL, Buck KN, Roe KL, Stuart RK, Allen AE, Mann EL, Johnson ZI, Barbeau KA (2018). Pervasive iron limitation at subsurface chlorophyll maxima of the California Current. Proc Natl Acad Sci U S A: 201813192. DOI: 10.1073/pnas.1813192115

The Second State of the Carbon Cycle Report (SOCCR2) was released by the U.S. Global Change Research Program (USGCRP) via https://carbon2018.globalchange.gov on Friday, November 23, 2018. With over 200 contributing experts including PI Johnson, this interagency Highly Influential Scientific Assessment was led by the Carbon Cycle Interagency Working Group (CCIWG) and U.S. Carbon Cycle Science Program under USGCRP auspices. SOCCR2 is an authoritative decadal assessment of carbon cycle science across North America, developed by over 200 experts from the U.S., Canadian and Mexican governments, national laboratories, universities, private sector, and research institutions. SOCCR2 is a Sustained Assessment Product of the U.S. Global Change Research Program.

USGCRP, 2018: Second State of the Carbon Cycle Report (SOCCR2): A Sustained Assessment Report. [Cavallaro, N., G. Shrestha, R. Birdsey, M. A. Mayes, R. G. Najjar, S. C. Reed, P. Romero-Lankao, and Z. Zhu (eds.)]. U.S. Global Change Research Program, Washington, DC, USA, 878 pp., https://doi.org/10.7930/SOCCR2.2018.

There is a growing awareness of the ecological and biogeochemical importance of fungi in coastal marine systems, while highly diverse fungi have been discovered in these marine systems, still little is known about their seasonality and associated drivers in coastal waters. Here, we examined fungal communities over three years of weekly samples at a dynamic, temperate coastal site (Piver’s Island Coastal Observatory (PICO), Beaufort NC USA). Fungal 18S rRNA gene abundance, OTU richness and Shannon’s diversity exhibited prominent seasonality. Fungi 18S rRNA gene copies peak in abundance during the summer and fall, with positive correlations with chlorophyll a, SiO4 and oxygen saturation. Diversity (measured using Internal Transcribed Spacer: ITS libraries) was highest during winter and lowest during summer; it was linked to temperature, pH, chlorophyll a, insolation, salinity, and DIC. Fungal community ITS libraries were dominated throughout the year by Ascomycota with contributions from Basidiomycota, Chytridiomycota and Mucoromycotina, with seasonal patterns linked to water temperature, light, and the carbonate system. Network analysis revealed that while co-occurrence and exclusion existed within fungal network, exclusion dominated the fungi and phytoplankton network, in contrast with reported pathogenic and nutritional interactions between marine phytoplankton and fungi. Compared with the seasonality of bacterial community in the same samples, the timing, extent and associated environmental variables for fungi community are unique. These results highlighted the fungal seasonal dynamics in coastal water and improve our understanding of the ecology of planktonic fungi.ImportanceCoastal fungal dynamics were long assumed to be due to terrestrial inputs; here, a high-resolution time-series, reveals strong, repeating annual patterns linked to in situ environmental conditions, arguing for a resident coastal fungal community shaped by environmental factors. These seasonal patterns do, however, differ from those observed in the bacterioplankton at the same site: e.g., fungal diversity peaks in winter whereas bacterial diversity maxima occur in the spring and fall. While dynamics of these communities are linked to water temperature and insolation, fungi are also influenced by the carbonate system (pH and DIC). As both fungi and heterotrophic bacteria are thought to be key organic material metabolizers, differences in their environmental drivers may offer clues as to which group dominates secondary production at this dynamic site. Overall, this study suggests the unique ecological roles of mycoplankton and their potentially broad niche complementarities to other microbial groups in the coastal ocean.

Duan Y, Xie N, Song Z, Ward CS, Yung C-M, Hunt DE, Johnson ZI, Wang G (2018). High-resolution Time-series Reveals Seasonal Patterns of Planktonic Fungi at a Temperate Coastal Ocean Site (Beaufort, North Carolina, USA). Appl Environ Microbiol. http://doi.org/10.1128/aem.00967-18

The unicellular Labyrinthulomycete protists have long been considered to play a significant role in ocean carbon cycling. However, their distribution and biogeochemical function remain poorly understood. We present a large‐scale study of their spatiotemporal abundance and diversity in the coastal waters of Bohai Sea using flow cytometry and high‐throughput sequencing. These protists display niche preferences and episodic higher biomass than that of bacterioplankton with much phylogenetic diversity (> 4000 OTUs) ever reported. They were ubiquitous with a typical abundance range of 100–1000 cells ml⁻¹ and biomass range of 0.06–574.59 μg C L⁻¹. The observed spatiotemporal abundance variations support the current ‘left‐over scavengers’ nutritional model and highlight these protists as a significant component of the marine microbial loop. The higher average abundance and phylogenetic diversity in the nearshore compared with those in the offshore reveal their predominant role in the terrigenous matter decomposition. Furthermore, the differential relationship of the protist genera to environmental conditions together with their co‐occurrence network suggests their unique substrate preferences and niche partitioning. With few subnetworks and possible keystone species, their network topology indicates community resilience and high connectance level of few operational taxonomic units (OTUs). We demonstrate the significant contribution of these protists to the secondary production and nutrient cycling in the coastal waters. As secondary producers, their role will become more important with increasingly coastal eutrophication.

Xie N, Sen B, Song Z , Zhao Y , Chen Z , Shi W , Zhang Y , Zhang J , Johnson ZI and Wang G (2018), High phylogenetic diversity and abundance pattern of Labyrinthulomycete protists in the coastal waters of the Bohai Sea. Environmental Microbiology . DOI:10.1111/1462-2920.14341