Cyanobacterial Diazotroph Distributions in the Western South Atlantic

Inputs of new nitrogen by cyanobacterial diazotrophs are critical to ocean ecosystem structure and function. Relative to other ocean regions, there is a lack of data on the distribution of these microbes in the western South Atlantic. Here, the abundance of six diazotroph phylotypes: Trichodesmium, Crocosphaera, UCYN-A, Richelia associated with Rhizosolenia (Het-1) or Hemiaulus (Het-2), and Calothrix associated with Chaetoceros (Het-3) was measured by quantitative PCR (qPCR) of the nifH gene along a transect extending from the shelf-break to the open ocean along the Vitória-Trindade seamount chain (1200 km). Using nifH gene copies as a proxy for phylotype abundance, Crocosphaera signals were the most abundant, with a broad distribution throughout the study region. Trichodesmium signals were the second most abundant, with the greatest numbers confined to the warmer waters closer to the coast, and a significant positive correlation with temperature. The average signals for the host-associated diazotrophs (UCYN-A, Het-1, and Het-2) were consistently lower than for the other phylotypes. These findings expand measurements of cyanobacterial diazotroph distribution in the western South Atlantic, and provide a new resource to enhance modeling studies focused on patterns of nitrogen fixation in the global ocean

Potentially toxigenic phytoplankton patterns in the northwestern Iberian Peninsula

The Galician estuaries are Europe’s foremost supplier of mussels, generating millions of euros annually and offering substantial employment opportunities for its population. One of the most critical threats to shellfish production is the occurrence of harmful algal blooms (HABs), contaminating bivalves with phytotoxins. To successfully tackle this problem, there needs to be a collaborative effort between the scientific community and decision-makers to establish a dynamic and effective monitoring system. This could enable early warnings and preventive actions to avert the loss of millions of tons of shellfish. Remote sensing, despite its limitations, requires commitment and effort by experts to devise effective methods for detecting target optical constituents mixed with other undesired target but that exhibit strong signals. Therefore, the essential necessity arises to identify approaches for mitigating the shortcomings of the undertaken efforts. The objective of this study is to assess the main environmental drivers of potential harmful genera (Pseudo-nitzschia, Dinophysis, Alexandrium, and Gymnodinium) in the Rías Baixas from 2015 to 2022, developing regression-based models and customizing Generalized Additive Models (GAMs) to investigate their spatial-temporal dynamics. Risk-susceptible bloom zones were identified in the river mouth of the Ría Pontevedra and from the center to offshore of the Ría Vigo. Early upwelling events triggered peaks in chlorophyll-a (Chl-a), driving Dinophysis grazing on phytoplankton communities mainly dominated by diatoms, flagellates, and ciliates. Subsequently, the upwelling intensity favoring Pseudo-nitzschia or Alexandrium minutum growth as larger diatoms declined. A. minutum exhibited elevated incidence over the past five years. Gymnodinium catenatum presented a rare occurrence across the three studied estuaries, which limited the assessment of its spatial dynamics in the region. This study emphasizes the need to integrate remote sensing evaluation of high-risk bloom areas (July to September), in-situ cell count collection, and enhanced efforts for forecasting future critical occurrences of HABs

Cyanobacterial Diazotroph Distributions in the Western South Atlantic

Inputs of new nitrogen by cyanobacterial diazotrophs are critical to ocean ecosystem structure and function. Relative to other ocean regions, there is a lack of data on the distribution of these microbes in the western South Atlantic. Here, the abundance of six diazotroph phylotypes: Trichodesmium, Crocosphaera, UCYN-A, Richelia associated with Rhizosolenia (Het-1) or Hemiaulus (Het-2), and Calothrix associated with Chaetoceros (Het-3) was measured by quantitative PCR (qPCR) of the nifH gene along a transect extending from the shelf-break to the open ocean along the Vitória-Trindade seamount chain (1200 km). Using nifH gene copies as a proxy for phylotype abundance, Crocosphaera signals were the most abundant, with a broad distribution throughout the study region. Trichodesmium signals were the second most abundant, with the greatest numbers confined to the warmer waters closer to the coast, and a significant positive correlation with temperature. The average signals for the host-associated diazotrophs (UCYN-A, Het-1, and Het-2) were consistently lower than for the other phylotypes. These findings expand measurements of cyanobacterial diazotroph distribution in the western South Atlantic, and provide a new resource to enhance modeling studies focused on patterns of nitrogen fixation in the global ocean.We are grateful for the project support from the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq, Projeto ILHAS Processes: 458583/2013-8). Postdoctoral support to AD was funded by the Coordination for the Improvement of Higher Education Personnel Foundation (CAPES, Proejto REMARSUL processes: 23038.004299/2014-53) for one year at the Lamont-Doherty Earth Observatory – Columbia University. This project was partly supported by the Gordon and Betty Moore Foundation Grant #4886 and US National Science Foundation grant 1737128 to AS

Chemotaxonomy-based mapping of phytoplankton communities in the subtropical Southwestern Atlantic Ocean, with emphasis on the marine cyanobacterium Trichodesmium

The composition and distribution of the phytoplankton community on the southweastern Brazilian continental shelf and continental slope were evaluated through chemotaxonomic analyses (HPLC-CHEMTAX). The samples were collected during five oceanographic cruises from 2012 to 2014 in spring and autumn. Fourteen surface blooms of Trichodesmium (slicks) were registered during the field surveys. The Trichodesmium biomass was estimated by both pigment analyses and microscope counts, with significant correlation found between the methods, except in some slicks. However, myxoxanthophyll, a Trichodesmium pigment biomarker generally used in CHEMTAX, was detectable only in seven samples from stations with Trichodesmium slicks, indicating that their use in pigment chemotaxonomic approaches should be taken with caution, because it could lead to errors in the estimation of Trichodesmium biomass. Four water masses were identified at the surface: Plata Plume Water (PPW), Subtropical Shelf Water (STSW), Shelf Water (SW) and Tropical Water (TW). The identified water masses seem to be the main driving factor influencing the composition, distribution and biomass of phytoplankton groups in the study region. The salty-warm oligotrophic TW, associated with the Brazil Current, was the dominant surface water mass in both autumn and spring. The surface waters in this work were generally associated with low values of both total chlorophyll a (TChl a) and nutrient concentration. In no slicks conditions, surface TChl a concentration was low ranging between 0.04 and 2.44 mg m−3 (mean 0.27 mg m−3) in almost all oceanographic stations. The highest biomass concentrations were recorded in stations under influence of both PPW and STSW. Overall, Prochlorococcus, haptophytes, Synechococcus, and Trichodesmium dominated the phytoplankton community and their contributions were above 70% to total Chl a in both spring and autumn. The other phytoplankton groups (prasinophytes, cryptophytes and dinoflagellates) represented a minor fraction, with values below 15% of the total biomass. A Canonical Correspondence Analysis showed that Prochlorococcus, haptophytes, Synechococcus and Trichodesmium were related with both TW and SW and were also positively associated with weaker water column stability, a deeper mixed layer, temperature and salinity. In turn, cryptophytes, dinoflagellates, prasynophytes and diatoms, mainly associated with STSW and PPW, were positively correlated with higher stability and nutrients (nitrogen and phosphorus), and negatively associated with both temperature and salinity. Our results showed that the pigment analysis (HPLC-CHEMTAX) allowed a detailed mapping of phytoplankton communities' distribution in the south and southeastern Brazilian continental shelf and shelf-break, and that the Trichodesmium biomass, as currently estimated by this approach, should be carefully revised

Mapping dinoflagellate blooms (Noctiluca and Alexandrium) in aquaculture production areas in theNWIberian Peninsulawith the Sentinel-2/3 satellites

14 pages, 8 figures, 1 table.-- Under a Creative Commons licenseThe Galician Rías (northwestern Spain) are periodically affected by harmful algal blooms (HABs), mostly dinoflagellates, which pose a challenge to aquaculture activities due to the accumulation of biotoxins in shellfish. Typically, reddish blooms in the Rías are associated with non-toxic species like Noctiluca scintillans, with a few exceptions such as Alexandrium minutum, a producer of paralytic shellfish toxins (PST). Here, a useful approach is presented for monitoring reddish blooms through satellite imagery based on three case studies, two of them belonged to monospecific blooms of red Noctiluca scintillans, and the third to a bloom of Alexandrium spp. dominated by A. tamarense. In every case, a propulsive index was evaluated using Sentinel-2A/B satellites, which provide high spatial and spectral resolutions, combined with adequate atmospheric and sunglint correction by using the ACOLITE and C2RCC processors. This approach offers a simple and feasible method to accurately and timely map blooms of red N. scintillans and Alexandrium spp. in the study area, useful to detect the distribution of reddish blooms with synoptic observations for monitoring and aquaculture management purposes. Conversely, Sentinel-3A/B satellites with a relatively coarser spatial resolution, lacking adequate visualization and mapping of the extent of small blooms, did not accurately detect bloom footprints in the coastal bay region, although this sensor displays a set of suitable multispectral bandsThis research was funded by projects RTI2018-098784-J-I00 (Sen2Coast) and CTM2017-86066-R funded by MCIN/AEI/10.13039/501100011033 and by “ERDF A way of making Europe”, the OAPN (Observatorio TIAMAT, REF: 2715/2021), the Andalusia Regional Government (PY20-00244) and the Axencia Galega de Innovación (agreement GAIN-IEO). The work was also supported by the grant PTA2019-016666-I funded by MCIN/AEI/10.13039/501100011033 and by “ESF Investing in your future” and by the grant IJC2019-039382-I funded by MCIN/AEI/10.13039/501100011033 and by “ERDF A way of making Europe”Peer reviewe

DataSheet_1_Cyanobacterial Diazotroph Distributions in the Western South Atlantic.docx

1 page. -- Figure S1. Temperature-salinity diagram of upper layer (20 m) for classification of the water masses and the distribution of Chl-a index in each water mass. TW = Tropical Water, and WSACW = West South Atlantic Central Water.Inputs of new nitrogen by cyanobacterial diazotrophs are critical to ocean ecosystem structure and function. Relative to other ocean regions, there is a lack of data on the distribution of these microbes in the western South Atlantic. Here, the abundance of six diazotroph phylotypes: Trichodesmium, Crocosphaera, UCYN-A, Richelia associated with Rhizosolenia (Het-1) or Hemiaulus (Het-2), and Calothrix associated with Chaetoceros (Het-3) was measured by quantitative PCR (qPCR) of the nifH gene along a transect extending from the shelf-break to the open ocean along the Vitória-Trindade seamount chain (1200 km). Using nifH gene copies as a proxy for phylotype abundance, Crocosphaera signals were the most abundant, with a broad distribution throughout the study region. Trichodesmium signals were the second most abundant, with the greatest numbers confined to the warmer waters closer to the coast, and a significant positive correlation with temperature. The average signals for the host-associated diazotrophs (UCYN-A, Het-1, and Het-2) were consistently lower than for the other phylotypes. These findings expand measurements of cyanobacterial diazotroph distribution in the western South Atlantic, and provide a new resource to enhance modeling studies focused on patterns of nitrogen fixation in the global ocean.Peer reviewe

Table_1_Cyanobacterial Diazotroph Distributions in the Western South Atlantic.docx

2 pages. -- Table S1. qPCR primers and probes used in this study for six diazotroph phylotypes. The phylotypes are as follows: UCYN-A, Crocosphaera, Trichodesmium, and three diatom symbionts including, Het-1 (Richelia-Rhizosolenia), Het-2 (Richelia-Hemiaulus), and Het-3 (Calothrix (Richelia –like)-Chaetoceros).Inputs of new nitrogen by cyanobacterial diazotrophs are critical to ocean ecosystem structure and function. Relative to other ocean regions, there is a lack of data on the distribution of these microbes in the western South Atlantic. Here, the abundance of six diazotroph phylotypes: Trichodesmium, Crocosphaera, UCYN-A, Richelia associated with Rhizosolenia (Het-1) or Hemiaulus (Het-2), and Calothrix associated with Chaetoceros (Het-3) was measured by quantitative PCR (qPCR) of the nifH gene along a transect extending from the shelf-break to the open ocean along the Vitória-Trindade seamount chain (1200 km). Using nifH gene copies as a proxy for phylotype abundance, Crocosphaera signals were the most abundant, with a broad distribution throughout the study region. Trichodesmium signals were the second most abundant, with the greatest numbers confined to the warmer waters closer to the coast, and a significant positive correlation with temperature. The average signals for the host-associated diazotrophs (UCYN-A, Het-1, and Het-2) were consistently lower than for the other phylotypes. These findings expand measurements of cyanobacterial diazotroph distribution in the western South Atlantic, and provide a new resource to enhance modeling studies focused on patterns of nitrogen fixation in the global ocean.Peer reviewe

Potentially toxigenic phytoplankton patterns in the northwestern Iberian Peninsula

14 pages, 7 figures, 2 tables.-- This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BYThe Galician estuaries are Europe’s foremost supplier of mussels, generating millions of euros annually and offering substantial employment opportunities for its population. One of the most critical threats to shellfish production is the occurrence of harmful algal blooms (HABs), contaminating bivalves with phytotoxins. To successfully tackle this problem, there needs to be a collaborative effort between the scientific community and decision-makers to establish a dynamic and effective monitoring system. This could enable early warnings and preventive actions to avert the loss of millions of tons of shellfish. Remote sensing, despite its limitations, requires commitment and effort by experts to devise effective methods for detecting target optical constituents mixed with other undesired target but that exhibit strong signals. Therefore, the essential necessity arises to identify approaches for mitigating the shortcomings of the undertaken efforts. The objective of this study is to assess the main environmental drivers of potential harmful genera (Pseudo-nitzschia, Dinophysis, Alexandrium, and Gymnodinium) in the Rías Baixas from 2015 to 2022, developing regression-based models and customizing Generalized Additive Models (GAMs) to investigate their spatial-temporal dynamics. Risk-susceptible bloom zones were identified in the river mouth of the Ría Pontevedra and from the center to offshore of the Ría Vigo. Early upwelling events triggered peaks in chlorophyll-a (Chl-a), driving Dinophysis grazing on phytoplankton communities mainly dominated by diatoms, flagellates, and ciliates. Subsequently, the upwelling intensity favoring Pseudo-nitzschia or Alexandrium minutum growth as larger diatoms declined. A. minutum exhibited elevated incidence over the past five years. Gymnodinium catenatum presented a rare occurrence across the three studied estuaries, which limited the assessment of its spatial dynamics in the region. This study emphasizes the need to integrate remote sensing evaluation of high-risk bloom areas (July to September), in-situ cell count collection, and enhanced efforts for forecasting future critical occurrences of HABsThis research has been financially supported by the agreement between the Spanish Ministry for Ecological Transition and Demographic Challenge and CSIC, funded by the European Union-Next Generation Program to contribute to the MSFD. This research was funded by projects from the OAPN (Observatorio TIAMAT, REF: 2715/2021), CTM2017-86066-R funded by MCIN/AEI/10.13039/501100011033 and by “ERDF A way of making Europe” and the Andalusia Regional Government (PY20-00244). The work was also supported by the grant PTA2019-016666-I funded by MCIN/AEI/10.13039/501100011033, the Programa Estatal Juan de la Cierva-Incorporación 2019 of the Spanish Ministry of Science and Innovation (IJC2019-039382-I), and the Grant CNS2023-143630 funded by MICIU/AEI/10.13039/501100011033 and by European Union Next Generation EU/PRTRPeer reviewe

Environmental conditions during phytoplankton blooms in the vicinity of james ross island, east of the antarctic peninsula

In waters surrounding James Ross Island (JRI), which is generally inaccessible, high chlorophyll-a concentration [Chla] can often be detected during summer periods by ocean color imagery. The region is influenced by a retreating sea ice edge from Weddell Sea and freshwater runoff from JRI glaciers, factors that probably trigger phytoplankton growth. In this work, we relate phytoplankton composition and biomass [Chla and carbon] with environmental factors in two successive late summer periods, in 2008 (1–3 March) and 2009 (17–20 February). Remote sensing data were used to corroborate the findings during those few sampling days. High surface [Chla] patches were observed through both remote sensing and field data (up to 7.61 mg Chla m-3 in 2009), and associated with a relatively shallow upper mixed layer (UML) (19–109 m in 2008 and 16–74 m in 2009). Sea surface temperatures were lower in 2008 (-1.19 to -0.62 C) than in 2009 (-0.87 to -0.46 C). Sea ice coverage was greater in 2008 than in 2009 summer, implying an earlier sea ice retreat in the latter year, when higher average [Chla] was obtained from field samples (3.3 mg m-3 , compared to 1.5 mg m-3 in 2008). The eastern side of JRI appeared to be relatively sheltered from the dominant pattern of largescale westerly winds. Diatoms dominated the phytoplankton community, with presence of large diatom species (e.g., Odontella weissflogii) typical of an advanced sea ice melt condition. Those blooms were sustained by a shallow UML associated with relative shelter from winds, due to proximity with the island

Base de données mondiale des diazotrophes océaniques version 2 et estimation élevée de la fixation de N 2 dans l'océan mondial

International audienceAbstract. Marine diazotrophs convert dinitrogen (N2) gas into bioavailable nitrogen (N), supporting life in the global ocean. In 2012, the first version of the global oceanic diazotroph database (version 1) was published. Here, we present an updated version of the database (version 2), significantly increasing the number of in situ diazotrophic measurements from 13 565 to 55 286. Data points for N2 fixation rates, diazotrophic cell abundance, and nifH gene copy abundance have increased by 184 %, 86 %, and 809 %, respectively. Version 2 includes two new data sheets for the nifH gene copy abundance of non-cyanobacterial diazotrophs and cell-specific N2 fixation rates. The measurements of N2 fixation rates approximately follow a log-normal distribution in both version 1 and version 2. However, version 2 considerably extends both the left and right tails of the distribution. Consequently, when estimating global oceanic N2 fixation rates using the geometric means of different ocean basins, version 1 and version 2 yield similar rates (43–57 versus 45–63 Tg N yr−1; ranges based on one geometric standard error). In contrast, when using arithmetic means, version 2 suggests a significantly higher rate of 223±30 Tg N yr−1 (mean ± standard error; same hereafter) compared to version 1 (74±7 Tg N yr−1). Specifically, substantial rate increases are estimated for the South Pacific Ocean (88±23 versus 20±2 Tg N yr−1), primarily driven by measurements in the southwestern subtropics, and for the North Atlantic Ocean (40±9 versus 10±2 Tg N yr−1). Moreover, version 2 estimates the N2 fixation rate in the Indian Ocean to be 35±14 Tg N yr−1, which could not be estimated using version 1 due to limited data availability. Furthermore, a comparison of N2 fixation rates obtained through different measurement methods at the same months, locations, and depths reveals that the conventional 15N2 bubble method yields lower rates in 69 % cases compared to the new 15N2 dissolution method. This updated version of the database can facilitate future studies in marine ecology and biogeochemistry. The database is stored at the Figshare repository (https://doi.org/10.6084/m9.figshare.21677687; Shao et al., 2022).Résumé. Les diazotrophes marins convertissent le diazote (N2) gazeux en azote (N) biodisponible, ce qui favorise la vie dans l'océan mondial. En 2012, la première version de la base de données mondiale des diazotrophes océaniques (version 1) a été publiée. Nous présentons ici une version actualisée de la base de données (version 2), augmentant de manière significative le nombre de mesures diazotrophiques in situ de 13 565 à 55 286. Les points de données pour les taux de fixation de N2, l'abondance des cellules diazotrophes et l'abondance des copies du gène nifH ont augmenté de 184 %, 86 % et 809 %, respectivement. La version 2 comprend deux nouvelles fiches de données pour l'abondance des copies du gène nifH des diazotrophes non cyanobactériens et les taux de fixation de N2 spécifiques aux cellules. Les mesures des taux de fixation N2 suivent approximativement une distribution log-normale dans les versions 1 et 2. Cependant, la version 2 étend considérablement les queues gauche et droite de la distribution. Par conséquent, lorsque l'on estime les taux de fixation de N2 dans l'océan mondial en utilisant les moyennes géométriques des différents bassins océaniques, la version 1 et la version 2 donnent des taux similaires (43-57 contre 45-63 Tg N an-1 ; fourchettes basées sur une erreur géométrique type). En revanche, lorsque l'on utilise les moyennes arithmétiques, la version 2 suggère un taux significativement plus élevé de 223±30 Tg N an-1 (moyenne ± erreur standard ; idem ci-après) par rapport à la version 1 (74±7 Tg N an-1). Plus précisément, des augmentations substantielles du taux sont estimées pour l'océan Pacifique Sud (88±23 contre 20±2 Tg N an-1), principalement grâce aux mesures effectuées dans les régions subtropicales du sud-ouest, et pour l'océan Atlantique Nord (40±9 contre 10±2 Tg N an-1). En outre, la version 2 estime le taux de fixation de N2 dans l'océan Indien à 35±14 Tg N an-1, ce qui n'a pas pu être estimé avec la version 1 en raison de la disponibilité limitée des données. En outre, une comparaison des taux de fixation de N2 obtenus par différentes méthodes de mesure aux mêmes mois, lieux et profondeurs révèle que la méthode conventionnelle des bulles de 15N2 donne des taux inférieurs dans 69 % des cas par rapport à la nouvelle méthode de dissolution de 15N2. Cette version actualisée de la base de données peut faciliter les études futures en écologie marine et en biogéochimie. La base de données est stockée dans le dépôt Figshare (https://doi.org/10.6084/m9.figshare.21677687 ; Shao et al., 2022)