Limnology and Oceanography最新文献

{"title":"Time series of phytoplankton net primary production reveals intense interannual variability and size‐dependent chlorophyll‐specific productivity on a continental shelf","authors":"Diana N. Fontaine, Pierre Marrec, Susanne Menden‐Deuer, Heidi M. Sosik, Tatiana A. Rynearson","doi":"10.1002/lno.12749","DOIUrl":"https://doi.org/10.1002/lno.12749","url":null,"abstract":"Phytoplankton community size structure influences the production and fate of organic carbon in marine food webs and can undergo strong seasonal shifts in temperate regions. As part of the Northeast US Shelf (NES) Long‐Term Ecological Research program, we measured net primary production (NPP) rates and chlorophyll <jats:italic>a</jats:italic> (Chl <jats:italic>a</jats:italic>) concentrations in three phytoplankton size classes (&lt; 5, 5–20, and &gt; 20 <jats:italic>μ</jats:italic>m) during winter and summer for 3 yr along a coastal‐to‐offshore transect. Mean depth‐integrated NPP was 37% higher in summer than winter, with limited cross‐shelf differences because of significant interannual variability. When averaged across the shelf, depth‐integrated NPP was dominated by the &gt; 20 <jats:italic>μ</jats:italic>m size class in winter and generated equally by the three size fractions in summer because of substantial contributions from cells &gt; 20 <jats:italic>μ</jats:italic>m at the Chl <jats:italic>a</jats:italic> maximum depth. Furthermore, the relationship between Chl <jats:italic>a</jats:italic> and NPP, in terms of relative contributions, varied by size class. Variations in this relationship have implications for models of primary productivity on the NES and beyond. In comparison to historical NPP data, we identified equivalent levels of winter NPP but observed a 25% decrease in summer NPP, suggesting a potential reduction in the seasonality of NPP on the NES. Together, our results highlight seasonal shifts in NPP rates of different phytoplankton size classes, with implications for food web structure and export production. These data emphasize the importance of quantifying size‐fractionated NPP over time to constrain its variability and better predict the fate of organic carbon in coastal systems under environmental change.","PeriodicalId":18143,"journal":{"name":"Limnology and Oceanography","volume":"23 1","pages":""},"PeriodicalIF":4.5,"publicationDate":"2024-12-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142776740","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Coupling of dimethylsulfoniopropionate production and carbon fixation in four temperate phytoplankton species excludes active short‐term regulation of dimethylsulfoniopropionate synthesis under increased light‐stress","authors":"Mareike G. Bach, Tamara Gademann, Maria A. van Leeuwe, J. Theo M. Elzenga, Jacqueline Stefels","doi":"10.1002/lno.12745","DOIUrl":"https://doi.org/10.1002/lno.12745","url":null,"abstract":"The production of the secondary metabolite dimethylsulfoniopropionate (DMSP) by marine microalgae has a strong impact on the global sulfur cycle, as DMSP is the precursor of the climate active gas dimethylsulfide. Quantifying the impact of abiotic parameters on DMSP production is needed to accurately depict DMSP production in ecosystem models. In this study, we investigated if de novo production of DMSP was upregulated under short‐term elevated irradiance and ultraviolet A radiation (UVA‐R). We exposed high‐light and low‐light acclimated cultures of <jats:italic>Emiliania huxleyi</jats:italic>, <jats:italic>Tetraselmis</jats:italic> sp., <jats:italic>Thalassiosira oceanica</jats:italic>, and <jats:italic>Phaeodactylum tricornutum</jats:italic> to high irradiance and UVA‐R treatments and followed de novo DMSP production and carbon fixation. We show that combined photosynthetically active radiation and UVA‐R resulted in increased net photoinhibition rates, but decreased specific DMSP production and growth compared to non‐UVA‐R treatments for all species. Photoacclimation to high photosynthetically active radiation resulted in a decreased UVA‐R sensitivity and positively affected the DMSP‐to‐carbon concentration ratios within the cultures. We conclude that there is no active short‐term upregulation of DMSP production under elevated photosynthetically active radiation and UVA‐R. Instead, the production of DMSP in response to light‐stress is closely coupled to particulate organic carbon production in all cases. While the relatively high cellular concentrations of DMSP do not exclude a de facto antioxidant function, its production is likely regulated by other cellular processes, for example, an overflow mechanism. The data of this study aim to improve the mechanistic understanding of DMSP synthesis, as well as to quantify DMSP production rates in different marine phytoplankton species.","PeriodicalId":18143,"journal":{"name":"Limnology and Oceanography","volume":"19 1","pages":""},"PeriodicalIF":4.5,"publicationDate":"2024-12-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142782615","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Effects of increased allochthonous dissolved organic carbon on the growth of planktonic biota in freshwater ecosystems: A meta‐analysis","authors":"Ruijing Ma, Misha Zhong, Qingyang Rao, Haojie Su, Ping Xie","doi":"10.1002/lno.12758","DOIUrl":"https://doi.org/10.1002/lno.12758","url":null,"abstract":"Water browning, induced by allochthonous dissolved organic carbon (DOC) input, has become a widespread phenomenon in boreal lakes over the past decades. Directly quantifying aquatic organisms' responses to increased DOC concentrations is essential for projecting carbon cycle processes in freshwater ecosystems. In this study, we assessed the impacts of DOC addition on the growth of three freshwater planktonic groups: phytoplankton, zooplankton, and bacteria, and explored potential drivers behind variations in effect size. Background DOC concentrations vary between 0.5 and 25 mg L<jats:sup>−1</jats:sup>, while total phosphorus concentrations span from 0.0003 to 1.55 mg L<jats:sup>−1</jats:sup>. Based on a meta‐analysis of 804 observations from 47 publications, we found that DOC addition had a significant positive effect on bacteria, while it had a small but negative impact on both phytoplankton and zooplankton. In different climate zones, DOC addition often stimulated bacterial growth, but it exerted either positive or negative effects on phytoplankton and zooplankton. Additionally, the effect sizes of both phytoplankton and zooplankton showed a significant negative relationship with the magnitude of DOC enrichment, while bacteria exhibited positive responses. Furthermore, the effect sizes of these three taxa correlated negatively with background total phosphorus concentrations and positively with the DOC : total phosphorus ratio. A significant negative correlation between effect size and experimental duration was observed for bacteria. In summary, this synthesis indicates that excessive DOC loading can inevitably inhibit phytoplankton and zooplankton growth. Future studies should focus on the interactions between DOC addition and global change factors to improve forecasts of carbon‐climate feedback in aquatic ecosystems.","PeriodicalId":18143,"journal":{"name":"Limnology and Oceanography","volume":"27 1","pages":""},"PeriodicalIF":4.5,"publicationDate":"2024-12-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142782614","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Seagrasses under stress: Independent negative effects of elevated temperature and light reduction at multiple levels of organization","authors":"Alissa V. Bass, Laura J. Falkenberg, Benoit Thibodeau","doi":"10.1002/lno.12759","DOIUrl":"https://doi.org/10.1002/lno.12759","url":null,"abstract":"Seagrasses are important foundation species, which support coastal biodiversity and provide socioeconomic benefits. However, seagrasses are threatened by anthropogenic changes, including the elevated temperature associated with marine heatwaves (MHWs) and light limitation from eutrophication or increased sedimentation. In this experiment, we exposed the seagrass <jats:italic>Halophila ovalis</jats:italic> to 10‐d of elevated temperature, simulating a MHW, and three light intensities to examine the impacts on multiple levels of organization, that is, growth, productivity, nitrogen cycling, and leaf microbiome. We found that both the MHW temperature and decreased light independently negatively impacted seagrass growth of new leaves, with decreased light also reducing new leaf area and rhizome elongation rate, and the occurrence of MHW temperatures increasing the rate of leaf loss. Similarly, chlorophyll concentration was altered by both stressors independently, with a common response to reduced light (increased chlorophyll concentration) significantly lower under the MHW temperature. Nitrogen assimilation rate into the leaves also decreased under both MHW temperature and reduced light availability. The leaf microbiome shifted in response to the MHW temperature and lower light, with these conditions prompting relatively more anaerobic microbes but less oxidative stress‐tolerant bacteria, and less prokaryotes performing phototrophy and (oxygenic) photoautotrophy. In conclusion, we show elevated temperature representing a MHW and light limitation can drive decreased seagrass growth, chlorophyll concentration, and cause shifts in leaf microbial functional groups, although there was little interaction between stressors. It is therefore important that good water clarity and habitat health is maintained to reduce the susceptibility of seagrasses to extreme climatic events.","PeriodicalId":18143,"journal":{"name":"Limnology and Oceanography","volume":"30 1","pages":""},"PeriodicalIF":4.5,"publicationDate":"2024-12-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142782613","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Local coral connections within an atoll reef system underlie reef resilience and persistence","authors":"Camille M. Grimaldi, Cal Faubel, Luke Thomas, Ayse D. Sahin, Nicole M. Ryan, Matt Rayson, Rebecca Green, Michael W. Cuttler, Eric A. Treml, Ryan. J. Lowe, James P. Gilmour","doi":"10.1002/lno.12720","DOIUrl":"https://doi.org/10.1002/lno.12720","url":null,"abstract":"The recovery of isolated reef systems is a complex process that is usually associated with the supply of coral larvae from distant reefs (or large‐scale connectivity). However, a frequently neglected process is the potential for supply within the reef itself (or local connectivity). In this study, we quantify and characterize the role of local connectivity over 21 yr of simulated annual coral spawning on an isolated coral reef atoll using outputs from a high‐resolution biophysical model (&lt; 150 m horizontal resolution) along with network analysis. We find that approximatively half of the coral reef larvae dispersal remains local (within 100 s m to 10 s km of release location), while the remaining half contributes to long‐distance dispersal (&gt; 100 s km) and is exported away from the system. Local dispersal plays a pivotal role in creating a highly‐connected network across the reef, enhancing exchanges of larvae within the same reef patches (local retention), across reef zones (e.g., lagoon, reef flat), and across the larger reef system. Finally, we show that this highly‐connected network exhibits a certain level of robustness, even when exposed to environmental stressors such as thermal‐induced mortality. Our findings highlight the previously overlooked role of local scale dispersal in driving recovery of isolated reef systems and emphasize the importance of targeted local management actions, indicating that efforts directed at enhancing and preserving local connectivity can have a substantial impact on the overall health and resilience of isolated reef ecosystems.","PeriodicalId":18143,"journal":{"name":"Limnology and Oceanography","volume":"15 1","pages":""},"PeriodicalIF":4.5,"publicationDate":"2024-12-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142776736","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Warming effects on a nonindigenous predator are not conserved across seasons","authors":"Nora Theurich, Ross N. Cuthbert, Elizabeta Briski","doi":"10.1002/lno.12747","DOIUrl":"https://doi.org/10.1002/lno.12747","url":null,"abstract":"The global proliferation of nonindigenous species remains a critical stressor driving both biodiversity loss and socioeconomic costs. These impacts frequently depend on environmental contexts, but few studies have investigated how seasonal variations coupled with climate changes, like warming, could modulate nonindigenous species ecological impacts. The Japanese brush‐clawed shore crab <jats:italic>Hemigrapsus takanoi</jats:italic> is a successful nonindigenous species in northern European waters and is currently spreading in the Baltic Sea. In this study, we used generalized linear models and the comparative functional response approach to examine the predatory impact of <jats:italic>H. takanoi</jats:italic> toward blue mussels <jats:italic>Mytilus</jats:italic> sp. across four seasons under current and future temperature scenarios (i.e., ambient and + 6°C warming). We further integrated <jats:italic>H. takanoi Q</jats:italic><jats:sub>10</jats:sub> values and field abundances across seasons to examine population‐level feeding impacts toward blue mussels. The nonindigenous species exhibited a consistent type II functional response (i.e., inversely prey density‐dependent response) across all seasons, temperatures and sexes, with males consistently consuming more mussels than females across all seasons. Warming generally decreased handling times and increased attack rates, but these effects varied by season and sex, with the most pronounced temperature responses observed in autumn and spring. Population‐level impact calculations integrating field abundance data of <jats:italic>H. takanoi</jats:italic> indicated that under ambient conditions, feeding impacts toward blue mussels currently peak in the summer months, but as temperature increases, this feeding impact is anticipated to shift later in the year into autumn. These findings underline the critical need for multifaceted research approaches to better understand and predict the context‐dependent ecological impacts of nonindigenous species, particularly in the face of ongoing climate change and shifting population characteristics.","PeriodicalId":18143,"journal":{"name":"Limnology and Oceanography","volume":"21 1","pages":""},"PeriodicalIF":4.5,"publicationDate":"2024-12-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142776775","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Patterns of siderophore production and utilization at Station ALOHA from the surface to mesopelagic waters","authors":"Randelle M. Bundy, Lauren E. Manck, Daniel J. Repeta, Matthew J. Church, Nicholas J. Hawco, Rene M. Boiteau, Jiwoon Park, Edward F. DeLong, Mak A. Saito","doi":"10.1002/lno.12746","DOIUrl":"https://doi.org/10.1002/lno.12746","url":null,"abstract":"The North Pacific subtropical gyre is a globally important contributor to carbon uptake despite being a persistently oligotrophic ecosystem. Supply of the micronutrient iron to the upper ocean varies seasonally to episodically, and when coupled with rapid biological consumption, results in low iron concentrations. In this study, we examined changes in iron uptake rates, along with siderophore concentrations and biosynthesis potential at Station ALOHA across time (2013–2016) and depth (surface to 500 m) to observe changes in iron acquisition and internal cycling by the microbial community. The genetic potential for siderophore biosynthesis was widespread throughout the upper water column, and biosynthetic gene clusters peaked in spring and summer along with siderophore concentrations, suggesting changes in nutrient delivery, primary production, and carbon export seasonally impact iron acquisition. Dissolved iron turnover times, calculated from iron‐amended experiments in surface (15 m) and mesopelagic (300 m) waters, ranged from 9 to 252 d. The shortest average turnover times at both depths were associated with inorganic iron additions (14 9 d) and the longest with iron bound to strong siderophores (148 225 d). Uptake rates of siderophore‐bound iron were faster in mesopelagic waters than in the surface, leading to high Fe : C uptake ratios of heterotrophic bacteria in the upper mesopelagic. The rapid cycling and high demand for iron at 300 m suggest differences in microbial metabolism and iron acquisition in the mesopelagic compared to surface waters. Together, changes in siderophore production and consumption over the seasonal cycle suggest organic carbon availability impacts iron cycling at Station ALOHA.","PeriodicalId":18143,"journal":{"name":"Limnology and Oceanography","volume":"26 1","pages":""},"PeriodicalIF":4.5,"publicationDate":"2024-12-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142763500","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Differential impacts of pH on growth, physiology, and elemental stoichiometry across three coccolithophore species","authors":"Nishant Chauhan, Rosalind E. M. Rickaby","doi":"10.1002/lno.12738","DOIUrl":"https://doi.org/10.1002/lno.12738","url":null,"abstract":"Coccolithophores are pivotal players in ocean biogeochemistry, yet the impact of changing pH on the physiology of different species remains unclear as there has been a dominant focus on <jats:italic>Gephyrocapsa huxleyi</jats:italic>. Meta‐analyses of existing experimental data are challenging due to the differences in multidimensional culture conditions. This study investigated the response of three species—<jats:italic>Gephyrocapsa huxleyi</jats:italic>, <jats:italic>Coccolithus braarudii</jats:italic>, and <jats:italic>Chrysotila carterae</jats:italic>—under varying CO<jats:sub>2</jats:sub> conditions (via pH). The sensitivity to pH differed between species, but all species showed reduced growth rates under the highest CO<jats:sub>2</jats:sub> (lowest pH) treatment possibly due to high [H<jats:sup>+</jats:sup>]‐related inhibition. Low pH impacted cellular physiology and elemental stoichiometry, while the impact of high pH was less adverse. The changes in elemental production induced by low pH could exert a negative influence on the contribution of coccolithophores to nutrient and carbon export, especially for biogeochemically relevant open‐ocean species. pH also affected coccolith formation, especially in <jats:italic>C. braarudii</jats:italic>, through CO<jats:sub>2</jats:sub> limitation at high pH and low calcite saturation state at low pH. Contrasting species‐specific pH sensitivities highlighted the potential for species like <jats:italic>G. huxleyi</jats:italic> to further outperform others like <jats:italic>C. braarudii</jats:italic> in an acidic ocean. Literature synthesis showed that coccolithophores show a broad CO<jats:sub>2</jats:sub> optimum, although growth rates and particulate inorganic carbon to particulate organic carbon ratios consistently declined with increasing CO<jats:sub>2</jats:sub>. Strain‐specific CO<jats:sub>2</jats:sub> optima partly contributed to the variability within responses of individual species, giving the misleading perception of a broad species‐level CO<jats:sub>2</jats:sub> optimum. Strain‐specific optima exist possibly due to their adaptation to carbonate chemistry conditions at the place of origin.","PeriodicalId":18143,"journal":{"name":"Limnology and Oceanography","volume":"56 1","pages":""},"PeriodicalIF":4.5,"publicationDate":"2024-12-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142763501","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Photoperiods and light differentially influence growth and potential niches of phycocyanin‐ and phycoerythrin‐rich picocyanobacteria","authors":"Sylwia Śliwińska‐Wilczewska, Marta Konik, Mireille Savoie, Anabella Aguilera, Naaman M. Omar, Douglas A. Campbell","doi":"10.1002/lno.12750","DOIUrl":"https://doi.org/10.1002/lno.12750","url":null,"abstract":"Strains from the picocyanobacteria genus <jats:italic>Synechococcus</jats:italic> are currently found across a wide range of photoperiods and photosynthetically active radiation. Future scenarios now forecast range expansions of marine <jats:italic>Synechococcus</jats:italic> into new photic regimes. We found that strains of temperate, coastal phycocyanin‐rich and phycoerythrin‐rich <jats:italic>Synechococcus</jats:italic> grew fastest under moderate photosynthetically active radiation, and a 24‐h photoperiod, despite a cumulative diel photon dose equivalent to conditions where growth was slower, under higher light and shorter photoperiods. Under optimal conditions, a phycoerythrin‐rich <jats:italic>Synechococcus</jats:italic> strain achieved a highest recorded cyanobacterial chlorophyll‐specific exponential growth rate (<jats:italic>μ</jats:italic>) of 4.5 d<jats:sup>−1</jats:sup>. Two phycoerythrin‐rich strains demonstrated wider ability to modulate light capture capacity, whereas two phycocyanin‐rich strains showed less change in light capture across increasing cumulative diel photon dose. All four coastal strains showed a decrease of effective absorption cross‐section for photosystem II photochemistry, vs. increasing cumulative diel photosynthetically active radiation doses. Within each strain, <jats:italic>μ</jats:italic> showed consistent, saturating responses to increasing cumulative diel photosystem II electron flux, with more variations in responses of <jats:italic>μ</jats:italic> to cumulative photosynthetically usable radiation. As photoperiod opportunists, coastal picocyanobacteria show potential to expand into longer photic regimes as higher latitudes warm.","PeriodicalId":18143,"journal":{"name":"Limnology and Oceanography","volume":"19 1","pages":""},"PeriodicalIF":4.5,"publicationDate":"2024-12-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142763503","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Consistent cell‐specific carbon fixation rates by small eukaryotic phytoplankton in contrasting nutrient‐limited conditions","authors":"Denise Rui Ying Ong, Andrés Gutiérrez‐Rodríguez, Karl A. Safi, Dominique Marie, Karen E. Selph, Michael R. Stukel, Moira Décima, Adriana Lopes dos Santos","doi":"10.1002/lno.12751","DOIUrl":"https://doi.org/10.1002/lno.12751","url":null,"abstract":"Small phytoplankton, consisting of pico and nano size fractions, are diverse in size and taxonomy. Yet, the differences in their productivity and taxonomic diversity are poorly described. Here, we measured the cell‐specific carbon fixation rates of picocyanobacteria <jats:italic>Synechococcus</jats:italic>, picoeukaryote, and nanoeukaryote populations, while unveiling their taxonomic composition in oligotrophic subtropical and high‐nutrient low‐chlorophyll subantarctic waters. We coupled 24 h in situ radiolabeled <jats:sup>14</jats:sup>C incubations to flow cytometry sorting and DNA metabarcoding from the same incubated samples, offering a direct account of the community associated with the carbon fixation rates measured. In both water masses, nanoeukaryotes had the highest cell‐specific carbon fixation rate, followed by picoeukaryotes and <jats:italic>Synechococcus</jats:italic> (2.24 ± 29.99, 2.18 ± 2.08, and 0.78 ± 0.55 fgC cell<jats:sup>−1</jats:sup> h<jats:sup>−1</jats:sup>, respectively). The cell‐specific carbon fixation rates and growth rates of <jats:italic>Synechococcus</jats:italic> were threefold higher in subtropical compared to subantarctic waters, while the rates of picoeukaryotes and nanoeukaryotes had no significant difference between the biogeochemically‐contrasting water masses. Sorted picoeukaryote populations were dominated by Mamiellophyceae, Pelagophyceae, Prymnesiophyceae, and Chrysophyceae, while nanoeukaryote populations were dominated by Dinophyceae and Prymnesiophyceae. Despite significant differences in their taxonomic composition, the sorted picoeukaryote populations in subantarctic waters and nanoeukaryote populations in subtropical and subantarctic waters were dominated by taxa reported in the literature as able to engage in phago‐mixotrophic strategies (Prymnesiophyceae, Chrysophyceae, and Dinophyceae), suggesting that such trophic strategy might be applied by discrete small photosynthetic eukaryote populations to alleviate macronutrient and iron stress.","PeriodicalId":18143,"journal":{"name":"Limnology and Oceanography","volume":"8 1","pages":""},"PeriodicalIF":4.5,"publicationDate":"2024-12-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142763597","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}