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Tracy A Villareal - One of the best experts on this subject based on the ideXlab platform.
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Isolation, growth, and nitrogen fixation rates of the Hemiaulus-Richelia (diatom-cyanobacterium) symbiosis in culture
PeerJ, 2020Co-Authors: Amy E. Pyle, Allison M. Johnson, Tracy A VillarealAbstract:Nitrogen fixers (diazotrophs) are often an important nitrogen source to phytoplankton nutrient budgets in N-limited marine environments. Diazotrophic symbioses between cyanobacteria and diatoms can dominate nitrogen-fixation regionally, particularly in major river plumes and in open ocean mesoscale blooms. This study reports the successful isolation and growth in monocultures of multiple strains of a diatom-cyanobacteria symbiosis from the Gulf of Mexico using a modified artificial seawater medium. We document the influence of light and nutrients on nitrogen fixation and growth rates of the host diatom Hemiaulus hauckii Grunow together with its diazotrophic endosymbiont Richelia intracellularis Schmidt, as well as less complete results on the Hemiaulus membranaceus-R. intracellularis symbiosis. The symbioses rates reported here are for the joint diatom-cyanobacteria unit. Symbiont diazotrophy was sufficient to support both the host diatom and cyanobacteria symbionts, and the entire symbiosis replicated and grew without added nitrogen. Maximum growth rates of multiple strains of H. hauckii symbioses in N-free medium with N2 as the sole N source were 0.74-0.93 div d-1. Growth rates followed light saturation kinetics in H. hauckii symbioses with a growth compensation light intensity (EC) of 7-16 µmol m-2s-1and saturation light level (EK) of 84-110 µmol m-2s-1. Nitrogen fixation rates by the symbiont while within the host followed a diel pattern where rates increased from near-zero in the scotophase to a maximum 4-6 h into the photophase. At the onset of the scotophase, nitrogen-fixation rates declined over several hours to near-zero values. Nitrogen fixation also exhibited light saturation kinetics. Maximum N2 fixation rates (84 fmol N2 heterocyst-1h-1) in low light adapted cultures (50 µmol m-2s-1) were approximately 40-50% of rates (144-154 fmol N2 heterocyst-1h-1) in high light (150 and 200 µmol m-2s-1) adapted cultures. Maximum laboratory N2 fixation rates were ~6 to 8-fold higher than literature-derived field rates of the H. hauckii symbiosis. In contrast to published results on the Rhizosolenia-Richelia symbiosis, the H. hauckii symbiosis did not use nitrate when added, although ammonium was consumed by the H. hauckii symbiosis. Symbiont-free host cell cultures could not be established; however, a symbiont-free H. hauckii strain was isolated directly from the field and grown on a nitrate-based medium that would not support DDA growth. Our observations together with literature reports raise the possibility that the asymbiotic H. hauckii are lines distinct from an obligately symbiotic H. hauckii line. While brief descriptions of successful culture isolation have been published, this report provides the first detailed description of the approaches, handling, and methodologies used for successful culture of this marine symbiosis. These techniques should permit a more widespread laboratory availability of these important marine symbioses.
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Summer diatom blooms in the eastern North Pacific gyre investigated with a long-endurance autonomous surface vehicle.
PeerJ, 2018Co-Authors: Emily E Anderson, Cara Wilson, Anthony H Knap, Tracy A VillarealAbstract:Satellite chlorophyll a (chl a) observations have repeatedly noted summertime phytoplankton blooms in the North Pacific subtropical gyre (NPSG), a region of open ocean that is far removed from any land-derived or Ekman upwelling nutrient sources. These blooms are dominated by N2-fixing diatom-cyanobacteria associations of the diatom genera Rhizosolenia Brightwell and Hemiaulus Ehrenberg. Their nitrogen fixing endosymbiont, Richelia intracellularis J.A. Schmidt, is hypothesized to be critical to the development of blooms in this nitrogen limited region. However, due to the remote location and unpredictable duration of the summer blooms, prolonged in situ observations are rare outside of the Station ALOHA time-series off of Hawai’i. In summer, 2015, a proof-of-concept mission using the autonomous vehicle, Honey Badger (Wave Glider SV2; Liquid Robotics, a Boeing company, Sunnyvale, CA, USA), collected near-surface (
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Summer diatom blooms in the eastern North Pacific gyre investigated with a long-endurance autonomous surface vehicle
2018Co-Authors: Emily E Anderson, Cara Wilson, Anthony H Knap, Tracy A VillarealAbstract:Satellite chlorophyll (chl) observations have repeatedly observed summertime phytoplankton blooms in the North Pacific subtropical gyre (NPSG), a region of open ocean that is far removed from any land-derived or Ekman upwelling nutrient sources. These blooms are dominated by N2-fixing diatom-cyanobacteria associations of the diatom genera Rhizosolenia Brightwell and Hemiaulus Ehrenberg. Their nitrogen fixing endosymbiont, Richelia intracellularis J.A. Schmidt, is hypothesized to be critical to the development of blooms in this nitrogen limited region. However, due to the remote location and unpredictable duration of the summer blooms, prolonged in situ observations are rare outside of the Station ALOHA time-series off of Hawai’i. In summer, 2015, a proof-of–concept mission using the autonomous vehicle, Honey Badger (Wave Glider SV2), collected near-surface (<20m) observations in the NPSG using hydrographic, meteorological, optical, and imaging sensors designed to focus on phytoplankton abundance, distribution and physiology of this bloom-forming region. Hemiaulus and Rhizosolenia cell abundance was determined using digital holography for the entire June-November mission. Honey Badger was not able to reach the 30°N subtropical front region where most of the satellite chl blooms have been observed, but near-real time navigational control allowed it to transect two blooms near 25°N. The two taxa did not co-occur in large numbers, rather the blooms were dominated by either Hemiaulus or Rhizosolenia. The 2-4 August 2015 bloom was comprised of 96% Hemiaulus and the second bloom, 15-17 August 2015, was dominated by Rhizosolenia (75%). The holograms also imaged undisturbed, fragile Hemiaulus aggregates throughout the sampled area at ~10 L-1. Aggregated Hemiaulus represented the entire observed population at times and had a widespread distribution independent of the SEP. Aggregate occurrence was not consistent with a density dependent formation mechanism and may represent a natural growth form in undisturbed conditions. The photosynthetic potential index (Fv:Fm) increased from ~0.4 to ~0.6 during both blooms indicating a physiologically robust phytoplankton community in the blooms. The diel pattern of Fv:Fm(nocturnal maximum; diurnal minimum) was consistent with macronutrient limitation throughout the mission with no evidence of Fe-limitation despite the presence of nitrogen fixing diatom-diazotroph assemblages. During the 5-month mission, Honey Badger covered ~5690 km (3070 nautical miles), acquired 9336 holograms, and reliably transmitted data onshore in near real-time. Software issues developed with the active fluorescence sensor that terminated measurements in early September. Although images were still useful at the end of the mission, fouling of the LISST-Holo optics was considerable, and appeared to be the most significant issue facing deployments of this duration.
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C 5 glycolipids of heterocystous cyanobacteria track symbiont abundance in the diatom Hemiaulus hauckii across the tropical North Atlantic
Biogeosciences, 2018Co-Authors: Nicole J. Bale, Jaap Sinninghe S Damste, Tracy A Villareal, Ellen C Hopmans, Corina P. D. Brussaard, Marc Besseling, Denise Dorhout, Stefan SchoutenAbstract:Abstract. Diatom–diazotroph associations (DDAs) include marine heterocystous cyanobacteria found as exosymbionts and endosymbionts in multiple diatom species. Heterocysts are the site of N2 fixation and have thickened cell walls containing unique heterocyst glycolipids which maintain a low oxygen environment within the heterocyst. The endosymbiotic cyanobacterium Richelia intracellularis found in species of the diatom genus Hemiaulus and Rhizosolenia makes heterocyst glycolipids (HGs) which are composed of C30 and C32 diols and triols with pentose (C5) moieties that are distinct from limnetic cyanobacterial HGs with predominantly hexose (C6) moieties. Here we applied a method for analysis of intact polar lipids to the study of HGs in suspended particulate matter (SPM) and surface sediment from across the tropical North Atlantic. The study focused on the Amazon plume region, where DDAs are documented to form extensive surface blooms, in order to examine the utility of C5 HGs as markers for DDAs as well as their transportation to underlying sediments. C30 and C32 triols with C5 pentose moieties were detected in both marine SPM and surface sediments. We found a significant correlation between the water column concentration of these long-chain C5 HGs and DDA symbiont counts. In particular, the concentrations of both the C5 HGs (1-(O-ribose)-3,27,29-triacontanetriol (C5 HG30 triol) and 1-(O-ribose)-3,29,31-dotriacontanetriol (C5 HG32 triol)) in SPM exhibited a significant correlation with the number of Hemiaulus hauckii symbionts. This result strengthens the idea that long-chain C5 HGs can be applied as biomarkers for marine endosymbiotic heterocystous cyanobacteria. The presence of the same C5 HGs in surface sediment provides evidence that they are effectively transported to the sediment and hence have potential as biomarkers for studies of the contribution of DDAs to the paleo-marine N cycle.
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C<sub>5</sub> glycolipids of heterocystous cyanobacteria track symbiont abundance in the diatom <i>Hemiaulus hauckii</i> across the tropical north Atlantic
2017Co-Authors: Nicole J. Bale, Tracy A Villareal, Ellen C Hopmans, Corina P. D. Brussaard, Marc Besseling, Denise Dorhout, Jaap S. Sinninghe Damsté, Stefan SchoutenAbstract:Abstract. Diatom-diazotroph associations (DDAs) include marine heterocystous cyanobacteria found as exoand endosymbionts in multiple diatom species. Heterocysts are the site of N2 fixation and have a thickened cell walls containing unique heterocyst glycolipids which maintain a low oxygen environment within the heterocyst. The endosymbiotic cyanobacteria Richelia intracellularis found in species of the diatom genus Hemiaulus and Rhizosolenia makes heterocyst glycolipids (HGs) containing pentose (C5) moieties that are distinct from limnetic cyanobacterial HGs with C6 moieties. Here we applied a method for analysis of intact polar lipids (IPLs) to the study of HGs in suspended particulate matter (SPM) and surface sediment from across the tropical North Atlantic. The study focused on the Amazon plume region where DDAs are documented to form extensive surface blooms in order to examine the utility of C5 HGs as markers for DDAs as well as their transportation to underlying sediments. C5 HGs were detected in both marine SPM and surface sediments. We found a significant correlation between the water column concentration of C5 HGs and DDA symbiont counts. In particular, the concentrations of both the C5 HGs (1-(O-ribose)-3,27,29-triacontanetriol (C5 HG30 triol) and 1-(O-ribose)- 3,29,31-dotriacontanetriol (C5 HG32 triol)) in SPM exhibited a significant correlation with the number of Hemiaulus hauckii symbionts. This result strengthens the idea that C5 HGs can be applied as biomarkers for marine endosymbiotic heterocystous cyanobacteria. The presence of the C5 HGs in surface sediment provides evidence that they are effectively transported to the sediment and hence have potential as biomarkers for studies of the contribution of DDAs to the paleo-marine N-cycle.
Jonathan P Zehr - One of the best experts on this subject based on the ideXlab platform.
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Metatranscriptomics of N_2-fixing cyanobacteria in the Amazon River plume
The ISME Journal, 2015Co-Authors: Jason A. Hilton, Brian Zielinski, Brandon M Satinsky, Mary Doherty, Jonathan P ZehrAbstract:Biological N_2 fixation is an important nitrogen source for surface ocean microbial communities. However, nearly all information on the diversity and gene expression of organisms responsible for oceanic N_2 fixation in the environment has come from targeted approaches that assay only a small number of genes and organisms. Using genomes of diazotrophic cyanobacteria to extract reads from extensive meta-genomic and -transcriptomic libraries, we examined diazotroph diversity and gene expression from the Amazon River plume, an area characterized by salinity and nutrient gradients. Diazotroph genome and transcript sequences were most abundant in the transitional waters compared with lower salinity or oceanic water masses. We were able to distinguish two genetically divergent phylotypes within the Hemiaulus -associated Richelia sequences, which were the most abundant diazotroph sequences in the data set. Photosystem (PS)-II transcripts in Richelia populations were much less abundant than those in Trichodesmium , and transcripts from several Richelia PS-II genes were absent, indicating a prominent role for cyclic electron transport in Richelia . In addition, there were several abundant regulatory transcripts, including one that targets a gene involved in PS-I cyclic electron transport in Richelia . High sequence coverage of the Richelia transcripts, as well as those from Trichodesmium populations, allowed us to identify expressed regions of the genomes that had been overlooked by genome annotations. High-coverage genomic and transcription analysis enabled the characterization of distinct phylotypes within diazotrophic populations, revealed a distinction in a core process between dominant populations and provided evidence for a prominent role for noncoding RNAs in microbial communities.
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Metatranscriptomics of N2-fixing cyanobacteria in the Amazon River plume
ISME Journal, 2015Co-Authors: Jason A. Hilton, Brian Zielinski, Brandon M Satinsky, Mary Doherty, Jonathan P ZehrAbstract:Biological N2 fixation is an important nitrogen source for surface ocean microbial communities. However, nearly all information on the diversity and gene expression of organisms responsible for oceanic N2 fixation in the environment has come from targeted approaches that assay only a small number of genes and organisms. Using genomes of diazotrophic cyanobacteria to extract reads from extensive meta-genomic and -transcriptomic libraries, we examined diazotroph diversity and gene expression from the Amazon River plume, an area characterized by salinity and nutrient gradients. Diazotroph genome and transcript sequences were most abundant in the transitional waters compared with lower salinity or oceanic water masses. We were able to distinguish two genetically divergent phylotypes within the Hemiaulus-associated Richelia sequences, which were the most abundant diazotroph sequences in the data set. Photosystem (PS)-II transcripts in Richelia populations were much less abundant than those in Trichodesmium, and transcripts from several Richelia PS-II genes were absent, indicating a prominent role for cyclic electron transport in Richelia. In addition, there were several abundant regulatory transcripts, including one that targets a gene involved in PS-I cyclic electron transport in Richelia. High sequence coverage of the Richelia transcripts, as well as those from Trichodesmium populations, allowed us to identify expressed regions of the genomes that had been overlooked by genome annotations. High-coverage genomic and transcription analysis enabled the characterization of distinct phylotypes within diazotrophic populations, revealed a distinction in a core process between dominant populations and provided evidence for a prominent role for noncoding RNAs in microbial communities.
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Genomic deletions disrupt nitrogen metabolism pathways of a cyanobacterial diatom symbiont
Nature communications, 2013Co-Authors: Jason A. Hilton, Rachel A Foster, Jonathan P Zehr, H. James Tripp, Brandon J. Carter, Tracy A VillarealAbstract:Diatoms with symbiotic N2-fixing cyanobacteria are often abundant in the oligotrophic open ocean gyres. The most abundant cyanobacterial symbionts form heterocysts (specialized cells for N2 fixation) and provide nitrogen (N) to their hosts, but their morphology, cellular locations and abundances differ depending on the host. Here we show that the location of the symbiont and its dependency on the host are linked to the evolution of the symbiont genome. The genome of Richelia (found inside the siliceous frustule of Hemiaulus) is reduced and lacks ammonium transporters, nitrate/nitrite reductases and glutamine:2-oxoglutarate aminotransferase. In contrast, the genome of the closely related Calothrix (found outside the frustule of Chaetoceros) is more similar to those of free-living heterocyst-forming cyanobacteria. The genome of Richelia is an example of metabolic streamlining that has implications for the evolution of N2-fixing symbiosis and potentially for manipulating plant–cyanobacterial interactions.
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Genomic deletions disrupt nitrogen metabolism pathways of a cyanobacterial diatom symbiont
Nature Communications, 2013Co-Authors: Jason A. Hilton, Rachel A Foster, Jonathan P Zehr, Brandon J. Carter, H. James Tripp, Tracy A VillarealAbstract:Diatoms with symbiotic N_2-fixing cyanobacteria are often abundant in the oligotrophic open ocean gyres. The most abundant cyanobacterial symbionts form heterocysts (specialized cells for N_2 fixation) and provide nitrogen (N) to their hosts, but their morphology, cellular locations and abundances differ depending on the host. Here we show that the location of the symbiont and its dependency on the host are linked to the evolution of the symbiont genome. The genome of Richelia (found inside the siliceous frustule of Hemiaulus ) is reduced and lacks ammonium transporters, nitrate/nitrite reductases and glutamine:2-oxoglutarate aminotransferase. In contrast, the genome of the closely related Calothrix (found outside the frustule of Chaetoceros ) is more similar to those of free-living heterocyst-forming cyanobacteria. The genome of Richelia is an example of metabolic streamlining that has implications for the evolution of N_2-fixing symbiosis and potentially for manipulating plant–cyanobacterial interactions. Cyanobacterial symbionts of marine diatoms can localize intracellularly or externally to their host partners. Here Hilton et al . describe the genomes of two diazotroph cyanobacterial symbionts of diatoms and show that the location of the symbiont affects expression of nitrogen assimilation genes.
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Distribution of diazotrophic microorganisms and nifH gene expression in the Mekong River plume during intermonsoon.
Marine Ecology Progress Series, 2011Co-Authors: Deniz Bombar, Rachel A Foster, Pia H Moisander, Maren Voss, Joachim W. Dippner, Birte Karfeld, Jonathan P ZehrAbstract:N2 fixation by marine pelagic prokaryotes plays a critical role in supplying new N to the ocean, and there is growing evidence that oceanic N2 fixation is generally enhanced in tropical river plumes, where N2 fixers (diazotrophs) benefit from riverine phosphorus and/or iron. Here we used nifH gene quantitative polymerase chain reaction (QPCR) and reverse transcription (RT) QPCR to investigate the horizontal distribution and activity of 9 diazotroph phylotypes in the Mekong River plume, South China Sea (SCS), in April 2007 (intermonsoon, lowest annual discharge). The nifH gene diversity was investigated by cloning and sequencing. Hydrodynamic modeling of the surface water advection revealed that the same water masses were sampled during the entire study, and helped to elucidate the physical forcing on diazotroph abundances and distributions. According to our esti- mates of nifH abundances and expression, the high N2 fixation rates detected in the Mekong plume can primarily be attributed to Trichodesmium spp. and the symbiotic diatom-diazotroph associations (DDAs) Rhizosolenia -Richelia and Hemiaulus -Richelia. NifH phylotypes from unicellular cyanobac- terial groups B and C and a gammaproteobacterial group (24774A11) were exclusively detected and expressed at oceanic stations. Clone libraries of nifH were dominated by Trichodesmium spp. but also included proteobacterial- and cluster III-like nifH sequences, including new lineages, possibly repre- senting other active diazotrophs in the Mekong plume and SCS offshore waters. This study extends the known distribution of quantitatively important oceanic diazotrophs, and shows that the Mekong River plume hosts a diverse diazotroph community, of which particularly Trichodesmium spp. and DDAs fix N2 at high rates.
Rachel A Foster - One of the best experts on this subject based on the ideXlab platform.
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Mesozooplankton Graze on Cyanobacteria in the Amazon River Plume and Western Tropical North Atlantic.
Frontiers in microbiology, 2017Co-Authors: Brandon J. Conroy, Deborah K Steinberg, Edward J. Carpenter, Bongkuen Song, Andrew Kalmbach, Rachel A FosterAbstract:Diazotrophic cyanobacteria, those capable of fixing di-nitrogen (N2), are considered one of the major sources of new nitrogen (N) in the oligotrophic tropical ocean, but direct incorporation of diazotrophic N into food webs has not been fully examined. In the Amazon River-influenced western tropical North Atlantic (WTNA), diatom diazotroph associations (DDAs) and the filamentous colonial diazotrophs Trichodesmium have seasonally high abundances. We sampled epipelagic mesozooplankton in the Amazon River plume and WTNA in May-June 2010 to investigate direct grazing by mesozooplankton on two DDA populations: Richelia associated with Rhizosolenia diatoms (het-1) and Hemiaulus diatoms (het-2), and on Trichodesmium using highly specific qPCR assays targeting nitrogenase genes (nifH). Both DDAs and Trichodesmium occurred in zooplankton gut contents, with higher detection of het-2 predominantly in calanoid copepods (2.33-16.76 nifH copies organism-1). Abundance of Trichodesmium was low (2.21-4.03 nifH copies organism-1), but they were consistently detected at high salinity stations (>35) in calanoid copepods. This suggests direct grazing on DDAs, Trichodesmium filaments and colonies, or consumption as part of sinking aggregates, is common. In parallel with the qPCR approach, a next generation sequencing (NGS) analysis of 16S rRNA genes identified that cyanobacterial assemblage associated with zooplankton guts was dominated by the non-diazotrophic unicellular phylotypes Synechococcus (56%) and Prochlorococcus (26%). However in two separate calanoid copepod samples, two unicellular diazotrophs Candidatus Atelocyanobacterium thalassa (UCYN-A) and Crocosphaera watsonii (UCYN-B) were present respectively, as a small component of cyanobacterial assemblages (< 2%). This study represents the first evidence of consumption of DDAs, Trichodesmium, and unicellular cyanobacteria by calanoid copepods in an area of the WTNA known for high carbon export. These diazotroph populations are quantitatively important in the global N budget, widespread and hence, the next step is to accurately quantify grazing. Nonetheless, these results highlight a direct pathway of diazotrophic N into the food web and have important implications for biogeochemical cycles, particularly oligotrophic regions where N2 fixation is the main source of new nitrogen.
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Genomic deletions disrupt nitrogen metabolism pathways of a cyanobacterial diatom symbiont
Nature communications, 2013Co-Authors: Jason A. Hilton, Rachel A Foster, Jonathan P Zehr, H. James Tripp, Brandon J. Carter, Tracy A VillarealAbstract:Diatoms with symbiotic N2-fixing cyanobacteria are often abundant in the oligotrophic open ocean gyres. The most abundant cyanobacterial symbionts form heterocysts (specialized cells for N2 fixation) and provide nitrogen (N) to their hosts, but their morphology, cellular locations and abundances differ depending on the host. Here we show that the location of the symbiont and its dependency on the host are linked to the evolution of the symbiont genome. The genome of Richelia (found inside the siliceous frustule of Hemiaulus) is reduced and lacks ammonium transporters, nitrate/nitrite reductases and glutamine:2-oxoglutarate aminotransferase. In contrast, the genome of the closely related Calothrix (found outside the frustule of Chaetoceros) is more similar to those of free-living heterocyst-forming cyanobacteria. The genome of Richelia is an example of metabolic streamlining that has implications for the evolution of N2-fixing symbiosis and potentially for manipulating plant–cyanobacterial interactions.
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Genomic deletions disrupt nitrogen metabolism pathways of a cyanobacterial diatom symbiont
Nature Communications, 2013Co-Authors: Jason A. Hilton, Rachel A Foster, Jonathan P Zehr, Brandon J. Carter, H. James Tripp, Tracy A VillarealAbstract:Diatoms with symbiotic N_2-fixing cyanobacteria are often abundant in the oligotrophic open ocean gyres. The most abundant cyanobacterial symbionts form heterocysts (specialized cells for N_2 fixation) and provide nitrogen (N) to their hosts, but their morphology, cellular locations and abundances differ depending on the host. Here we show that the location of the symbiont and its dependency on the host are linked to the evolution of the symbiont genome. The genome of Richelia (found inside the siliceous frustule of Hemiaulus ) is reduced and lacks ammonium transporters, nitrate/nitrite reductases and glutamine:2-oxoglutarate aminotransferase. In contrast, the genome of the closely related Calothrix (found outside the frustule of Chaetoceros ) is more similar to those of free-living heterocyst-forming cyanobacteria. The genome of Richelia is an example of metabolic streamlining that has implications for the evolution of N_2-fixing symbiosis and potentially for manipulating plant–cyanobacterial interactions. Cyanobacterial symbionts of marine diatoms can localize intracellularly or externally to their host partners. Here Hilton et al . describe the genomes of two diazotroph cyanobacterial symbionts of diatoms and show that the location of the symbiont affects expression of nitrogen assimilation genes.
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Impact of diatom‐diazotroph associations on carbon export in the Amazon River plume
Geophysical Research Letters, 2012Co-Authors: Laurence Y Yeung, E D Young, Maria G Prokopenko, Victoria J Coles, Joseph P Montoya, Deborah K Steinberg, Edward J. Carpenter, Nick E Rollins, William M Berelson, Rachel A FosterAbstract:[1] Offshore tropical river plumes are associated with areas of high N2 fixation (diazotrophy) and biological carbon drawdown. Episodic blooms of the diatom Hemiaulus hauckii and its diazotrophic cyanobacterial symbiont Richelia intracellularisare believed to dominate that carbon drawdown, but the mechanism is not well understood. We report primary productivity associated with blooms of these diatom-diazotroph assemblages (DDAs) in the offshore plume of the Amazon River using simultaneous measurements of O2/Ar ratios and the triple-isotope composition of dissolved O2. In these blooms, we observe peaks in net community productivity, but relatively small changes in gross primary productivity, suggesting that DDA blooms increase the ecosystem carbon export ratio more than twofold. These events of enhanced export efficiency lead to biological uptake of dissolved inorganic carbon and silicate, whose longer mixed-layer residence times otherwise obscure the differential impact of DDAs. The shorter-term rate estimates presented here are consistent with the results derived from longer-term geochemical tracers, confirming that DDAs drive a significant biological CO2 pump in tropical oceans.
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impact of diatom diazotroph associations on carbon export in the amazon river plume
Geophysical Research Letters, 2012Co-Authors: Laurence Y Yeung, E D Young, Maria G Prokopenko, Victoria J Coles, Joseph P Montoya, Deborah K Steinberg, Edward J. Carpenter, Nick E Rollins, William M Berelson, Rachel A FosterAbstract:[1] Offshore tropical river plumes are associated with areas of high N2 fixation (diazotrophy) and biological carbon drawdown. Episodic blooms of the diatom Hemiaulus hauckii and its diazotrophic cyanobacterial symbiont Richelia intracellularisare believed to dominate that carbon drawdown, but the mechanism is not well understood. We report primary productivity associated with blooms of these diatom-diazotroph assemblages (DDAs) in the offshore plume of the Amazon River using simultaneous measurements of O2/Ar ratios and the triple-isotope composition of dissolved O2. In these blooms, we observe peaks in net community productivity, but relatively small changes in gross primary productivity, suggesting that DDA blooms increase the ecosystem carbon export ratio more than twofold. These events of enhanced export efficiency lead to biological uptake of dissolved inorganic carbon and silicate, whose longer mixed-layer residence times otherwise obscure the differential impact of DDAs. The shorter-term rate estimates presented here are consistent with the results derived from longer-term geochemical tracers, confirming that DDAs drive a significant biological CO2 pump in tropical oceans.
Cara Wilson - One of the best experts on this subject based on the ideXlab platform.
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Summer diatom blooms in the eastern North Pacific gyre investigated with a long-endurance autonomous surface vehicle.
PeerJ, 2018Co-Authors: Emily E Anderson, Cara Wilson, Anthony H Knap, Tracy A VillarealAbstract:Satellite chlorophyll a (chl a) observations have repeatedly noted summertime phytoplankton blooms in the North Pacific subtropical gyre (NPSG), a region of open ocean that is far removed from any land-derived or Ekman upwelling nutrient sources. These blooms are dominated by N2-fixing diatom-cyanobacteria associations of the diatom genera Rhizosolenia Brightwell and Hemiaulus Ehrenberg. Their nitrogen fixing endosymbiont, Richelia intracellularis J.A. Schmidt, is hypothesized to be critical to the development of blooms in this nitrogen limited region. However, due to the remote location and unpredictable duration of the summer blooms, prolonged in situ observations are rare outside of the Station ALOHA time-series off of Hawai’i. In summer, 2015, a proof-of-concept mission using the autonomous vehicle, Honey Badger (Wave Glider SV2; Liquid Robotics, a Boeing company, Sunnyvale, CA, USA), collected near-surface (
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Summer diatom blooms in the eastern North Pacific gyre investigated with a long-endurance autonomous surface vehicle
2018Co-Authors: Emily E Anderson, Cara Wilson, Anthony H Knap, Tracy A VillarealAbstract:Satellite chlorophyll (chl) observations have repeatedly observed summertime phytoplankton blooms in the North Pacific subtropical gyre (NPSG), a region of open ocean that is far removed from any land-derived or Ekman upwelling nutrient sources. These blooms are dominated by N2-fixing diatom-cyanobacteria associations of the diatom genera Rhizosolenia Brightwell and Hemiaulus Ehrenberg. Their nitrogen fixing endosymbiont, Richelia intracellularis J.A. Schmidt, is hypothesized to be critical to the development of blooms in this nitrogen limited region. However, due to the remote location and unpredictable duration of the summer blooms, prolonged in situ observations are rare outside of the Station ALOHA time-series off of Hawai’i. In summer, 2015, a proof-of–concept mission using the autonomous vehicle, Honey Badger (Wave Glider SV2), collected near-surface (<20m) observations in the NPSG using hydrographic, meteorological, optical, and imaging sensors designed to focus on phytoplankton abundance, distribution and physiology of this bloom-forming region. Hemiaulus and Rhizosolenia cell abundance was determined using digital holography for the entire June-November mission. Honey Badger was not able to reach the 30°N subtropical front region where most of the satellite chl blooms have been observed, but near-real time navigational control allowed it to transect two blooms near 25°N. The two taxa did not co-occur in large numbers, rather the blooms were dominated by either Hemiaulus or Rhizosolenia. The 2-4 August 2015 bloom was comprised of 96% Hemiaulus and the second bloom, 15-17 August 2015, was dominated by Rhizosolenia (75%). The holograms also imaged undisturbed, fragile Hemiaulus aggregates throughout the sampled area at ~10 L-1. Aggregated Hemiaulus represented the entire observed population at times and had a widespread distribution independent of the SEP. Aggregate occurrence was not consistent with a density dependent formation mechanism and may represent a natural growth form in undisturbed conditions. The photosynthetic potential index (Fv:Fm) increased from ~0.4 to ~0.6 during both blooms indicating a physiologically robust phytoplankton community in the blooms. The diel pattern of Fv:Fm(nocturnal maximum; diurnal minimum) was consistent with macronutrient limitation throughout the mission with no evidence of Fe-limitation despite the presence of nitrogen fixing diatom-diazotroph assemblages. During the 5-month mission, Honey Badger covered ~5690 km (3070 nautical miles), acquired 9336 holograms, and reliably transmitted data onshore in near real-time. Software issues developed with the active fluorescence sensor that terminated measurements in early September. Although images were still useful at the end of the mission, fouling of the LISST-Holo optics was considerable, and appeared to be the most significant issue facing deployments of this duration.
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Summer Diatom Blooms in the North Pacific Subtropical Gyre: 2008–2009
2016Co-Authors: Tracy A Villareal, Jeffrey W. Krause, Mark A. Brzezinski, Colbi G. Brown, Cara WilsonAbstract:The summertime North Pacific subtropical gyre has widespread phytoplankton blooms between Hawaii and the subtropical front (,30uN) that appear as chlorophyll (chl) increases in satellite ocean color data. Nitrogen-fixing diatom symbioses (diatom-diazotroph associations: DDAs) often increase 102–103 fold in these blooms and contribute to elevated export flux. In 2008 and 2009, two cruises targeted satellite chlorophyll blooms to examine DDA species abundance, chlorophyll concentration, biogenic silica concentration, and hydrography. Generalized observations that DDA blooms occur when the mixed layer depth is, 70 m are supported, but there is no consistent relationship between mixed layer depth, bloom intensity, or composition; regional blooms between 22–34uN occur within a broader temperature range (21–26uC) than previously reported. In both years, the Hemiaulus-Richelia and Rhizosolenia-Richelia DDAs increased 102–103 over background concentrations within satellite-defined bloom features. The two years share a common trend of Hemiaulus dominance of the DDAs and substantial increases in the.10 mm chl a fraction (,40–90+ % of total chl a). Integrated diatom abundance varied 10-fold over,10 km. Biogenic silica concentration tracked diatom abundance, was dominated by the.10 mm size fraction, and increased up to 5-fold in the blooms. The two years differed in the magnitude of the surface chl a increase (2009.2008), the abundance of pennate diatoms within the bloom (2009.2008), and the substantially greater mixed layer depth in 2009. Only the 2009 bloom had sufficient chl a in the.10 mm fraction to produce the observed ocean color chl increase. Blooms had high spatial variability; ocean color images likely average over numerous small events ove
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biogenic silica cycling during summer phytoplankton blooms in the north pacific subtropical gyre
Deep Sea Research Part I: Oceanographic Research Papers, 2013Co-Authors: Jeffrey W. Krause, Mark A. Brzezinski, Tracy A Villareal, Cara WilsonAbstract:Abstract Biogenic silica (bSiO 2 ) cycling, diatom abundance and floristics were examined within summer-period diatom blooms in the North Pacific Subtropical Gyre (NPSG) in 2008 and 2009. Hemiaulus hauckii was the most abundant diatom observed in an expansive (100,000 km 2 ) bloom near the subtropical front in the northeastern NPSG in 2008 and the small pennate diatom Mastogloia woodiana dominated a smaller (30,000 km 2 ) bloom sampled in 2009 in the gyre interior. In both blooms, the bSiO 2 stock and production rates were up to an order of magnitude higher relative to non-bloom areas. Remnants of a bSiO 2 export event was sampled in the H. hauckii bloom area where the export rate at 300 m exceeded that at 150 m, and was among the highest values recorded in the NPSG. The M. woodiana bloom was very active with specific bSiO 2 production rates of 0.50–0.75 d −1 and net bSiO 2 production rates were among the highest observed in any subtropical-gyre diatom bloom to date. Net silica production rates in the euphotic zone were strongly positive within blooms and near zero outside of blooms, consistent with an important role for blooms in bSiO 2 export. The difference in the areal extent of the H. hauckii and M. woodiana blooms was consistent with remote-sensing observations that blooms in the northeastern portion of the NPSG, near the subtropical front, are typically more extensive than those in the gyre interior near Hawaii Ocean Time-series station ALOHA. Initial estimates suggest that blooms in the northeast region produced 3–25 times more bSiO 2 in 2008 and 2009, respectively, than did blooms in the gyre interior; and due to the large areal extent these blooms, their area-integrated production of bSiO 2 is similar to intense diatom blooms coastal upwelling systems (e.g. Monterey Bay, Santa Barbara Channel) despite significantly lower production rates and standing stock.
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Species/abundance summary for the 2008/2009 blooms.
2012Co-Authors: Tracy A Villareal, Jeffrey W. Krause, Mark A. Brzezinski, Colbi G. Brown, Cara WilsonAbstract:Histograms express 0–60 m integrated abundance values for the DDA Hemiaulus hauckii. Individual columns are labeled with year (station number) for reference to the onion plots. The onion plots express the relative species abundance at stations for each year with each taxon color-coded (see Table 1, 2 for numerical data).
Edward J. Carpenter - One of the best experts on this subject based on the ideXlab platform.
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The Influence of Riverine Nutrients in Niche Partitioning of Phytoplankton Communities–A Contrast Between the Amazon River Plume and the Changjiang (Yangtze) River Diluted Water of the East China Sea
Frontiers Media S.A., 2018Co-Authors: Helga Do Rosario Gomes, Edward J. Carpenter, Patricia L. Yager, Joji Ishizaka, Joaquim I. GoesAbstract:Riverine nutrients act in concert with local hydrographic conditions to create distinct ecological niches for phytoplankton communities across river-ocean continuums. Here we compare two of the world’s largest river-ocean systems, the Amazon River Plume (ARP) which outflows into the Western Tropical North Atlantic and the Changjiang Diluted Water (CDW) which empties into the East China Sea to show how distinctly different N: P supply ratios of their source waters, shape phytoplankton communities along the river-ocean continuum. Sampling in the relatively unpolluted surface waters of the ARP during peak river discharge revealed that phytoplankton communities along the river-ocean continuum were strongly limited by Dissolved Inorganic Nitrogen (DIN, nitrate plus nitrite) which was low or beyond detectable, while Dissolved Inorganic Phosphorous (DIP, phosphate) and Silica were not limiting. The resulting low N:P supply ratio allowed diazotrophs to co-exist with non-diazotrophs. Diatom-Diazotroph Associations (DDAs) such as Hemiaulus hauckii-Richelia proliferated, while in the oligotrophic oceanic waters, Trichodesmium spp. thrived. In contrast, in the CDW, anthropogenic nitrogen inputs from human pressures in the Changjiang River system has led to a system where the changing supply rate of the single nutrient (DIP) is responsible for the interannual variability seen in the phytoplankton community structure of the CDW. During years of low discharge, DIP limitation can be ameliorated by on-shelf upwelling of DIP rich Kuroshio Intermediate Waters leading to domination of diatoms and dinoflagellates. Conversely, during years of heavy discharge, the westward flowing CDW plume was severely DIP limited, probably because water column stratification dampened upwelling of subsurface waters. The consequent DIP limitation led to the proliferation of small phytoplankton such as Chlorophytes and Cyanobacteria. The absence of diazotrophs in the CDW, leads us to hypothesize that river-ocean continuums, whose source waters are heavily impacted by anthropogenic activities and with high nitrate concentrations often substantially in excess of Redfield ratios, may not support diatoms offshore on account of DIP limitation nor diazotrophy because of excess DIN
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Mesozooplankton Graze on Cyanobacteria in the Amazon River Plume and Western Tropical North Atlantic.
Frontiers in microbiology, 2017Co-Authors: Brandon J. Conroy, Deborah K Steinberg, Edward J. Carpenter, Bongkuen Song, Andrew Kalmbach, Rachel A FosterAbstract:Diazotrophic cyanobacteria, those capable of fixing di-nitrogen (N2), are considered one of the major sources of new nitrogen (N) in the oligotrophic tropical ocean, but direct incorporation of diazotrophic N into food webs has not been fully examined. In the Amazon River-influenced western tropical North Atlantic (WTNA), diatom diazotroph associations (DDAs) and the filamentous colonial diazotrophs Trichodesmium have seasonally high abundances. We sampled epipelagic mesozooplankton in the Amazon River plume and WTNA in May-June 2010 to investigate direct grazing by mesozooplankton on two DDA populations: Richelia associated with Rhizosolenia diatoms (het-1) and Hemiaulus diatoms (het-2), and on Trichodesmium using highly specific qPCR assays targeting nitrogenase genes (nifH). Both DDAs and Trichodesmium occurred in zooplankton gut contents, with higher detection of het-2 predominantly in calanoid copepods (2.33-16.76 nifH copies organism-1). Abundance of Trichodesmium was low (2.21-4.03 nifH copies organism-1), but they were consistently detected at high salinity stations (>35) in calanoid copepods. This suggests direct grazing on DDAs, Trichodesmium filaments and colonies, or consumption as part of sinking aggregates, is common. In parallel with the qPCR approach, a next generation sequencing (NGS) analysis of 16S rRNA genes identified that cyanobacterial assemblage associated with zooplankton guts was dominated by the non-diazotrophic unicellular phylotypes Synechococcus (56%) and Prochlorococcus (26%). However in two separate calanoid copepod samples, two unicellular diazotrophs Candidatus Atelocyanobacterium thalassa (UCYN-A) and Crocosphaera watsonii (UCYN-B) were present respectively, as a small component of cyanobacterial assemblages (< 2%). This study represents the first evidence of consumption of DDAs, Trichodesmium, and unicellular cyanobacteria by calanoid copepods in an area of the WTNA known for high carbon export. These diazotroph populations are quantitatively important in the global N budget, widespread and hence, the next step is to accurately quantify grazing. Nonetheless, these results highlight a direct pathway of diazotrophic N into the food web and have important implications for biogeochemical cycles, particularly oligotrophic regions where N2 fixation is the main source of new nitrogen.
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Amazon River influence on nitrogen fixation and export production in the western tropical North Atlantic
Limnology and Oceanography, 2016Co-Authors: Sarah C. Weber, Victoria J Coles, Edward J. Carpenter, Patricia L. Yager, Joaquim I. Goes, Joseph P MontoyaAbstract:As part of the ANACONDAS program, we investigated the role of the Amazon plume in stimulating offshore nitrogen fixation and export production during the river's high-discharge period (May–June 2010). Using the shipboard underway system, we performed high-resolution sampling of over 450,000 km2 of surface waters, characterizing the distribution of nutrients, phytoplankton, particulate organic matter (POM), and stable carbon and nitrogen isotopes of POM in the offshore plume. We found distinct regional variations in diazotroph communities, with the Diatom-Diazotroph Associations (DDA) Hemiaulus hauckii – Richelia intracellularis dominating the low N : P mesohaline waters to the northwest of the plume axis and Trichodesmium spp. primarily occupying oceanic waters to the east. Nutrient availability broadly shaped diazotroph distributions along the salinity gradient, but habitat longevity may also play a role in the finer-scale distributions of communities, particularly of DDAs. H. hauckii and Trichodesmium spp. affected the nitrogen and carbon budgets in fundamentally different ways within the plume-influenced regions, with H. hauckii making much greater contributions to the particulate nitrogen pool and to CO2 drawdown than Trichodesmium spp., leading to much higher export fluxes. Our findings provide an important constraint on the role of the Amazon plume in creating distinct niches and roles for diazotrophs in the nutrient and carbon budgets of the western tropical North Atlantic.
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Impact of diatom‐diazotroph associations on carbon export in the Amazon River plume
Geophysical Research Letters, 2012Co-Authors: Laurence Y Yeung, E D Young, Maria G Prokopenko, Victoria J Coles, Joseph P Montoya, Deborah K Steinberg, Edward J. Carpenter, Nick E Rollins, William M Berelson, Rachel A FosterAbstract:[1] Offshore tropical river plumes are associated with areas of high N2 fixation (diazotrophy) and biological carbon drawdown. Episodic blooms of the diatom Hemiaulus hauckii and its diazotrophic cyanobacterial symbiont Richelia intracellularisare believed to dominate that carbon drawdown, but the mechanism is not well understood. We report primary productivity associated with blooms of these diatom-diazotroph assemblages (DDAs) in the offshore plume of the Amazon River using simultaneous measurements of O2/Ar ratios and the triple-isotope composition of dissolved O2. In these blooms, we observe peaks in net community productivity, but relatively small changes in gross primary productivity, suggesting that DDA blooms increase the ecosystem carbon export ratio more than twofold. These events of enhanced export efficiency lead to biological uptake of dissolved inorganic carbon and silicate, whose longer mixed-layer residence times otherwise obscure the differential impact of DDAs. The shorter-term rate estimates presented here are consistent with the results derived from longer-term geochemical tracers, confirming that DDAs drive a significant biological CO2 pump in tropical oceans.
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impact of diatom diazotroph associations on carbon export in the amazon river plume
Geophysical Research Letters, 2012Co-Authors: Laurence Y Yeung, E D Young, Maria G Prokopenko, Victoria J Coles, Joseph P Montoya, Deborah K Steinberg, Edward J. Carpenter, Nick E Rollins, William M Berelson, Rachel A FosterAbstract:[1] Offshore tropical river plumes are associated with areas of high N2 fixation (diazotrophy) and biological carbon drawdown. Episodic blooms of the diatom Hemiaulus hauckii and its diazotrophic cyanobacterial symbiont Richelia intracellularisare believed to dominate that carbon drawdown, but the mechanism is not well understood. We report primary productivity associated with blooms of these diatom-diazotroph assemblages (DDAs) in the offshore plume of the Amazon River using simultaneous measurements of O2/Ar ratios and the triple-isotope composition of dissolved O2. In these blooms, we observe peaks in net community productivity, but relatively small changes in gross primary productivity, suggesting that DDA blooms increase the ecosystem carbon export ratio more than twofold. These events of enhanced export efficiency lead to biological uptake of dissolved inorganic carbon and silicate, whose longer mixed-layer residence times otherwise obscure the differential impact of DDAs. The shorter-term rate estimates presented here are consistent with the results derived from longer-term geochemical tracers, confirming that DDAs drive a significant biological CO2 pump in tropical oceans.