1
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Glaze TD, Erler DV, Siljanen HMP. Microbially facilitated nitrogen cycling in tropical corals. THE ISME JOURNAL 2022; 16:68-77. [PMID: 34226659 PMCID: PMC8692614 DOI: 10.1038/s41396-021-01038-1] [Citation(s) in RCA: 13] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/07/2020] [Revised: 06/04/2021] [Accepted: 06/08/2021] [Indexed: 02/06/2023]
Abstract
Tropical scleractinian corals support a diverse assemblage of microbial symbionts. This 'microbiome' possesses the requisite functional diversity to conduct a range of nitrogen (N) transformations including denitrification, nitrification, nitrogen fixation and dissimilatory nitrate reduction to ammonium (DNRA). Very little direct evidence has been presented to date verifying that these processes are active within tropical corals. Here we use a combination of stable isotope techniques, nutrient uptake calculations and captured metagenomics to quantify rates of nitrogen cycling processes in a selection of tropical scleractinian corals. Denitrification activity was detected in all species, albeit with very low rates, signifying limited importance in holobiont N removal. Relatively greater nitrogen fixation activity confirms that corals are net N importers to reef systems. Low net nitrification activity suggests limited N regeneration capacity; however substantial gross nitrification activity may be concealed through nitrate consumption. Based on nrfA gene abundance and measured inorganic N fluxes, we calculated significant DNRA activity in the studied corals, which has important implications for coral reef N cycling and warrants more targeted investigation. Through the quantification and characterisation of all relevant N-cycling processes, this study provides clarity on the subject of tropical coral-associated biogeochemical N-cycling.
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Affiliation(s)
- Thomas D Glaze
- Centre for Coastal Biogeochemistry Research, School of Environment Science and Engineering, Southern Cross University, Lismore, NSW, Australia.
| | - Dirk V Erler
- Centre for Coastal Biogeochemistry Research, School of Environment Science and Engineering, Southern Cross University, Lismore, NSW, Australia
| | - Henri M P Siljanen
- Department of Environmental and Biological Sciences, University of Eastern Finland, Kuopio, Finland
- Department of Ecogenomics and Systems Biology, University of Vienna, Vienna, Austria
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2
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Moynihan MA, Goodkin NF, Morgan KM, Kho PYY, Lopes Dos Santos A, Lauro FM, Baker DM, Martin P. Coral-associated nitrogen fixation rates and diazotrophic diversity on a nutrient-replete equatorial reef. THE ISME JOURNAL 2022; 16:233-246. [PMID: 34294880 PMCID: PMC8692400 DOI: 10.1038/s41396-021-01054-1] [Citation(s) in RCA: 13] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/10/2020] [Revised: 06/23/2021] [Accepted: 06/30/2021] [Indexed: 02/07/2023]
Abstract
The role of diazotrophs in coral physiology and reef biogeochemistry remains poorly understood, in part because N2 fixation rates and diazotrophic community composition have only been jointly analyzed in the tissue of one tropical coral species. We performed field-based 15N2 tracer incubations during nutrient-replete conditions to measure diazotroph-derived nitrogen (DDN) assimilation into three species of scleractinian coral (Pocillopora acuta, Goniopora columna, Platygyra sinensis). Using multi-marker metabarcoding (16S rRNA, nifH, 18S rRNA), we analyzed DNA- and RNA-based communities in coral tissue and skeleton. Despite low N2 fixation rates, DDN assimilation supplied up to 6% of the holobiont's N demand. Active coral-associated diazotrophs were chiefly Cluster I (aerobes or facultative anaerobes), suggesting that oxygen may control coral-associated diazotrophy. Highest N2 fixation rates were observed in the endolithic community (0.20 µg N cm-2 per day). While the diazotrophic community was similar between the tissue and skeleton, RNA:DNA ratios indicate potential differences in relative diazotrophic activity between these compartments. In Pocillopora, DDN was found in endolithic, host, and symbiont compartments, while diazotrophic nifH sequences were only observed in the endolithic layer, suggesting a possible DDN exchange between the endolithic community and the overlying coral tissue. Our findings demonstrate that coral-associated diazotrophy is significant, even in nutrient-rich waters, and suggest that endolithic microbes are major contributors to coral nitrogen cycling on reefs.
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Affiliation(s)
- Molly A Moynihan
- Earth Observatory of Singapore, Interdisciplinary Graduate School, Nanyang Technological University, Singapore, Singapore.
- Asian School of the Environment, Nanyang Technological University, Singapore, Singapore.
| | - Nathalie F Goodkin
- Asian School of the Environment, Nanyang Technological University, Singapore, Singapore
- Earth Observatory of Singapore, Nanyang Technological University, Singapore, Singapore
- American Museum of Natural History, New York, NY, USA
| | - Kyle M Morgan
- Asian School of the Environment, Nanyang Technological University, Singapore, Singapore
| | - Phyllis Y Y Kho
- Asian School of the Environment, Nanyang Technological University, Singapore, Singapore
| | | | - Federico M Lauro
- Asian School of the Environment, Nanyang Technological University, Singapore, Singapore
- Singapore Centre for Environmental Life Sciences Engineering (SCELSE), Nanyang Technological University, Singapore, Singapore
| | - David M Baker
- Division for Ecology and Biodiversity, School of Biological Sciences, University of Hong Kong, Hong Kong, PR China
- The Swire Institute of Marine Science, University of Hong Kong, Hong Kong, PR China
| | - Patrick Martin
- Asian School of the Environment, Nanyang Technological University, Singapore, Singapore
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3
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Bednarz VN, van de Water JAJM, Grover R, Maguer JF, Fine M, Ferrier-Pagès C. Unravelling the Importance of Diazotrophy in Corals - Combined Assessment of Nitrogen Assimilation, Diazotrophic Community and Natural Stable Isotope Signatures. Front Microbiol 2021; 12:631244. [PMID: 34248863 PMCID: PMC8264265 DOI: 10.3389/fmicb.2021.631244] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2020] [Accepted: 05/28/2021] [Indexed: 11/22/2022] Open
Abstract
There is an increasing interest in understanding the structure and function of the microbiota associated with marine and terrestrial organisms, because it can play a major role in host nutrition and resistance to environmental stress. Reef-building corals live in association with diazotrophs, which are microbes able to fix dinitrogen. Corals are known to assimilate diazotrophically-derived nitrogen (DDN), but it is still not clear whether this nitrogen source is derived from coral-associated diazotrophs and whether it substantially contributes to the coral’s nitrogen budget. In this study, we aimed to provide a better understanding of the importance of DDN for corals using a holistic approach by simultaneously assessing DDN assimilation rates (using 15N2 tracer technique), the diazotrophic bacterial community (using nifH gene amplicon sequencing) and the natural δ15N signature in Stylophora pistillata corals from the Northern Red Sea along a depth gradient in winter and summer. Overall, our results show a discrepancy between the three parameters. DDN was assimilated by the coral holobiont during winter only, with an increased assimilation with depth. Assimilation rates were, however, not linked to the presence of coral-associated diazotrophs, suggesting that the presence of nifH genes does not necessarily imply functionality. It also suggests that DDN assimilation was independent from coral-associated diazotrophs and may instead result from nitrogen derived from planktonic diazotrophs. In addition, the δ15N signature presented negative values in almost all coral samples in both seasons, suggesting that nitrogen sources other than DDN contribute to the nitrogen budget of corals from this region. This study yields novel insight into the origin and importance of diazotrophy for scleractinian corals from the Northern Red Sea using multiple proxies.
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Affiliation(s)
- Vanessa N Bednarz
- Marine Department, Centre Scientifique de Monaco, Monaco City, Monaco
| | | | - Renaud Grover
- Marine Department, Centre Scientifique de Monaco, Monaco City, Monaco
| | - Jean-François Maguer
- Laboratoire des Sciences de l'Environnement Marin (LEMAR), UMR 6539 UBO/CNRS/IRD/IFREMER, Institut Universitaire Européen de la Mer, Plouzané, France
| | - Maoz Fine
- Mina and Everard Goodman Faculty of Life Sciences, Bar-Ilan University, Ramat Gan, Israel.,The Interuniversity Institute for Marine Sciences, Eilat, Israel
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4
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Pupier CA, Grover R, Fine M, Rottier C, van de Water JAJM, Ferrier-Pagès C. Dissolved Nitrogen Acquisition in the Symbioses of Soft and Hard Corals With Symbiodiniaceae: A Key to Understanding Their Different Nutritional Strategies? Front Microbiol 2021; 12:657759. [PMID: 34149646 PMCID: PMC8211778 DOI: 10.3389/fmicb.2021.657759] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2021] [Accepted: 04/23/2021] [Indexed: 11/13/2022] Open
Abstract
Nitrogen is one of the limiting nutrients for coral growth and primary productivity. Therefore, the capacity of different associations between corals and their algal symbionts (Symbiodiniaceae) to efficiently exploit the available nitrogen sources will influence their distribution and abundance. Recent studies have advanced our understanding of nitrogen assimilation in reef-building scleractinian (hard) coral-Symbiodiniaceae symbioses. However, the nutrient metabolism of other coral taxa, such as Alcyoniina (soft corals), remains underexplored. Using stable isotope labeling, we investigated the assimilation of dissolved nitrogen (i.e., ammonium, nitrate, and free amino acids) by multiple species of soft and hard corals sampled in the Gulf of Aqaba in shallow (8-10 m) and mesophotic (40-50 m) reefs. Our results show that dissolved nitrogen assimilation rates per tissue biomass were up to 10-fold higher in hard than in soft coral symbioses for all sources of nitrogen. Although such differences in assimilation rates could be linked to the Symbiodiniaceae density, Symbiodiniaceae species, or the C:N ratio of the host and algal symbiont fractions, none of these parameters were different between the two coral taxa. Instead, the lower assimilation rates in soft coral symbioses might be explained by their different nutritional strategy: whereas soft corals may obtain most of their nitrogen via the capture of planktonic prey by the coral host (heterotrophic feeding), hard corals may rely more on dissolved nitrogen assimilation by their algal symbionts to fulfill their needs. This study highlights different nutritional strategies in soft and hard coral symbioses. A higher reliance on heterotrophy may help soft corals to grow in reefs with higher turbidity, which have a high concentration of particles in suspension in seawater. Further, soft corals may benefit from lower dissolved nitrogen assimilation rates in areas with low water quality.
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Affiliation(s)
- Chloé A. Pupier
- Marine Department, Centre Scientifique de Monaco, Monaco, Monaco
- Collège Doctoral, Sorbonne Université, Paris, France
| | - Renaud Grover
- Marine Department, Centre Scientifique de Monaco, Monaco, Monaco
| | - Maoz Fine
- The Goodman Faculty of Life Sciences, Bar-Ilan University, Ramat Gan, Israel
- The Interuniversity Institute for Marine Science in Eilat, Eilat, Israel
| | - Cécile Rottier
- Marine Department, Centre Scientifique de Monaco, Monaco, Monaco
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5
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El-Khaled YC, Roth F, Rädecker N, Tilstra A, Karcher DB, Kürten B, Jones BH, Voolstra CR, Wild C. Nitrogen fixation and denitrification activity differ between coral- and algae-dominated Red Sea reefs. Sci Rep 2021; 11:11820. [PMID: 34083565 PMCID: PMC8175748 DOI: 10.1038/s41598-021-90204-8] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2020] [Accepted: 05/07/2021] [Indexed: 11/18/2022] Open
Abstract
Coral reefs experience phase shifts from coral- to algae-dominated benthic communities, which could affect the interplay between processes introducing and removing bioavailable nitrogen. However, the magnitude of such processes, i.e., dinitrogen (N2) fixation and denitrification levels, and their responses to phase shifts remain unknown in coral reefs. We assessed both processes for the dominant species of six benthic categories (hard corals, soft corals, turf algae, coral rubble, biogenic rock, and reef sands) accounting for > 98% of the benthic cover of a central Red Sea coral reef. Rates were extrapolated to the relative benthic cover of the studied organisms in co-occurring coral- and algae-dominated areas of the same reef. In general, benthic categories with high N2 fixation exhibited low denitrification activity. Extrapolated to the respective reef area, turf algae and coral rubble accounted for > 90% of overall N2 fixation, whereas corals contributed to more than half of reef denitrification. Total N2 fixation was twice as high in algae- compared to coral-dominated areas, whereas denitrification levels were similar. We conclude that algae-dominated reefs promote new nitrogen input through enhanced N2 fixation and comparatively low denitrification. The subsequent increased nitrogen availability could support net productivity, resulting in a positive feedback loop that increases the competitive advantage of algae over corals in reefs that experienced a phase shift.
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Affiliation(s)
- Yusuf C El-Khaled
- Marine Ecology Department, Faculty of Biology and Chemistry, University of Bremen, 28359, Bremen, Germany.
| | - Florian Roth
- Red Sea Research Center, King Abdullah University of Science and Technology (KAUST), Thuwal, 23995, Saudi Arabia
- Baltic Sea Centre, Stockholm University, 10691, Stockholm, Sweden
- Faculty of Biological and Environmental Sciences, Tvärminne Zoological Station, University of Helsinki, 00014, Helsinki, Finland
| | - Nils Rädecker
- Red Sea Research Center, King Abdullah University of Science and Technology (KAUST), Thuwal, 23995, Saudi Arabia
- Department of Biology, University of Konstanz, 78457, Konstanz, Germany
- Laboratory for Biological Geochemistry, School of Architecture, Civil and Environmental Engineering, École Polytechnique Fédérale de Lausanne (EPFL), 1015, Lausanne, Switzerland
| | - Arjen Tilstra
- Marine Ecology Department, Faculty of Biology and Chemistry, University of Bremen, 28359, Bremen, Germany
| | - Denis B Karcher
- Marine Ecology Department, Faculty of Biology and Chemistry, University of Bremen, 28359, Bremen, Germany
- Australian National Centre for the Public Awareness of Science, Australian National University, ACT, Canberra, 2601, Australia
| | - Benjamin Kürten
- Red Sea Research Center, King Abdullah University of Science and Technology (KAUST), Thuwal, 23995, Saudi Arabia
- Project Management Jülich, Jülich Research Centre GmbH, 18069, Rostock, Germany
| | - Burton H Jones
- Red Sea Research Center, King Abdullah University of Science and Technology (KAUST), Thuwal, 23995, Saudi Arabia
| | - Christian R Voolstra
- Red Sea Research Center, King Abdullah University of Science and Technology (KAUST), Thuwal, 23995, Saudi Arabia
- Department of Biology, University of Konstanz, 78457, Konstanz, Germany
| | - Christian Wild
- Marine Ecology Department, Faculty of Biology and Chemistry, University of Bremen, 28359, Bremen, Germany
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6
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Roth F, Karcher DB, Rädecker N, Hohn S, Carvalho S, Thomson T, Saalmann F, Voolstra CR, Kürten B, Struck U, Jones BH, Wild C. High rates of carbon and dinitrogen fixation suggest a critical role of benthic pioneer communities in the energy and nutrient dynamics of coral reefs. Funct Ecol 2020. [DOI: 10.1111/1365-2435.13625] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Affiliation(s)
- Florian Roth
- Red Sea Research Center King Abdullah University of Science and Technology (KAUST) Thuwal Saudi Arabia
- Baltic Sea Centre Stockholm University Stockholm Sweden
- Faculty of Biological and Environmental Sciences Tvärminne Zoological Station University of Helsinki Helsinki Finland
| | - Denis B. Karcher
- Marine Ecology Faculty of Biology and Chemistry University of Bremen Bremen Germany
| | - Nils Rädecker
- Red Sea Research Center King Abdullah University of Science and Technology (KAUST) Thuwal Saudi Arabia
- Laboratory for Biological Geochemistry School of Architecture Civil and Environmental Engineering Ecole Polytechnique Fédérale de Lausanne (EPFL) Lausanne Switzerland
| | - Sönke Hohn
- Systems Ecology Group Department of Theoretical Ecology and Modelling Leibniz Centre for Tropical Marine Research Bremen Germany
| | - Susana Carvalho
- Red Sea Research Center King Abdullah University of Science and Technology (KAUST) Thuwal Saudi Arabia
| | - Timothy Thomson
- Red Sea Research Center King Abdullah University of Science and Technology (KAUST) Thuwal Saudi Arabia
| | - Franziska Saalmann
- Marine Ecology Faculty of Biology and Chemistry University of Bremen Bremen Germany
- Faculty of Science and Engineering University of Groningen Groningen The Netherlands
| | - Christian R. Voolstra
- Red Sea Research Center King Abdullah University of Science and Technology (KAUST) Thuwal Saudi Arabia
- Department of Biology University of Konstanz Konstanz Germany
| | - Benjamin Kürten
- Red Sea Research Center King Abdullah University of Science and Technology (KAUST) Thuwal Saudi Arabia
- Jülich Research Centre GmbHProject Management Jülich Rostock Germany
| | - Ulrich Struck
- Museum für Naturkunde Leibniz Institute for Evolution and Biodiversity Science Berlin Germany
- Department of Earth Sciences Freie Universität Berlin Berlin Germany
| | - Burton H. Jones
- Red Sea Research Center King Abdullah University of Science and Technology (KAUST) Thuwal Saudi Arabia
| | - Christian Wild
- Marine Ecology Faculty of Biology and Chemistry University of Bremen Bremen Germany
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7
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Tilstra A, El-Khaled YC, Roth F, Rädecker N, Pogoreutz C, Voolstra CR, Wild C. Denitrification Aligns with N 2 Fixation in Red Sea Corals. Sci Rep 2019; 9:19460. [PMID: 31857601 PMCID: PMC6923481 DOI: 10.1038/s41598-019-55408-z] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2019] [Accepted: 11/26/2019] [Indexed: 12/27/2022] Open
Abstract
Denitrification may potentially alleviate excess nitrogen (N) availability in coral holobionts to maintain a favourable N to phosphorous ratio in the coral tissue. However, little is known about the abundance and activity of denitrifiers in the coral holobiont. The present study used the nirS marker gene as a proxy for denitrification potential along with measurements of denitrification rates in a comparative coral taxonomic framework from the Red Sea: Acropora hemprichii, Millepora dichotoma, and Pleuractis granulosa. Relative nirS gene copy numbers associated with the tissues of these common corals were assessed and compared with denitrification rates on the holobiont level. In addition, dinitrogen (N2) fixation rates, Symbiodiniaceae cell density, and oxygen evolution were assessed to provide an environmental context for denitrification. We found that relative abundances of the nirS gene were 16- and 17-fold higher in A. hemprichii compared to M. dichotoma and P. granulosa, respectively. In concordance, highest denitrification rates were measured in A. hemprichii, followed by M. dichotoma and P. granulosa. Denitrification rates were positively correlated with N2 fixation rates and Symbiodiniaceae cell densities. Our results suggest that denitrification may counterbalance the N input from N2 fixation in the coral holobiont, and we hypothesize that these processes may be limited by photosynthates released by the Symbiodiniaceae.
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Affiliation(s)
- Arjen Tilstra
- Marine Ecology Department, Faculty of Biology and Chemistry, University of Bremen, Bremen, 28359, Germany.
| | - Yusuf C El-Khaled
- Marine Ecology Department, Faculty of Biology and Chemistry, University of Bremen, Bremen, 28359, Germany
| | - Florian Roth
- Red Sea Research Center, King Abdullah University of Science and Technology, Thuwal, 23955-6900, Kingdom of Saudi Arabia
| | - Nils Rädecker
- Red Sea Research Center, King Abdullah University of Science and Technology, Thuwal, 23955-6900, Kingdom of Saudi Arabia
| | - Claudia Pogoreutz
- Red Sea Research Center, King Abdullah University of Science and Technology, Thuwal, 23955-6900, Kingdom of Saudi Arabia
| | - Christian R Voolstra
- Red Sea Research Center, King Abdullah University of Science and Technology, Thuwal, 23955-6900, Kingdom of Saudi Arabia
- Department of Biology, University of Konstanz, Konstanz, 78464, Germany
| | - Christian Wild
- Marine Ecology Department, Faculty of Biology and Chemistry, University of Bremen, Bremen, 28359, Germany
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8
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Morris LA, Voolstra CR, Quigley KM, Bourne DG, Bay LK. Nutrient Availability and Metabolism Affect the Stability of Coral-Symbiodiniaceae Symbioses. Trends Microbiol 2019; 27:678-689. [PMID: 30987816 DOI: 10.1016/j.tim.2019.03.004] [Citation(s) in RCA: 116] [Impact Index Per Article: 23.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2018] [Revised: 02/28/2019] [Accepted: 03/13/2019] [Indexed: 01/19/2023]
Abstract
Coral reefs rely upon the highly optimized coral-Symbiodiniaceae symbiosis, making them sensitive to environmental change and susceptible to anthropogenic stress. Coral bleaching is predominantly attributed to photo-oxidative stress, yet nutrient availability and metabolism underpin the stability of symbioses. Recent studies link symbiont proliferation under nutrient enrichment to bleaching; however, the interactions between nutrients and symbiotic stability are nuanced. Here, we demonstrate how bleaching is regulated by the forms and ratios of available nutrients and their impacts on autotrophic carbon metabolism, rather than algal symbiont growth. By extension, historical nutrient conditions mediate host-symbiont compatibility and bleaching tolerance over proximate and evolutionary timescales. Renewed investigations into the coral nutrient metabolism will be required to truly elucidate the cellular mechanisms leading to coral bleaching.
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Affiliation(s)
- Luke A Morris
- AIMS@JCU, Australian Institute of Marine Science, College of Science and Engineering, James Cook University, Townsville, Australia; Australian Institute of Marine Science, Townsville, Australia; College of Science and Engineering, James Cook University, Townsville, Australia. https://twitter.com/ReefLuke
| | - Christian R Voolstra
- Red Sea Research Center, Division of Biological and Environmental Science and Engineering, King Abdullah University of Science and Technology (KAUST), Thuwal, Saudi Arabia. https://twitter.com/reefgenomics
| | - Kate M Quigley
- AIMS@JCU, Australian Institute of Marine Science, College of Science and Engineering, James Cook University, Townsville, Australia; Australian Institute of Marine Science, Townsville, Australia. https://twitter.com/la__cientifica
| | - David G Bourne
- AIMS@JCU, Australian Institute of Marine Science, College of Science and Engineering, James Cook University, Townsville, Australia; Australian Institute of Marine Science, Townsville, Australia; College of Science and Engineering, James Cook University, Townsville, Australia
| | - Line K Bay
- AIMS@JCU, Australian Institute of Marine Science, College of Science and Engineering, James Cook University, Townsville, Australia; Australian Institute of Marine Science, Townsville, Australia.
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9
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Tilstra A, van Hoytema N, Cardini U, Bednarz VN, Rix L, Naumann MS, Al-Horani FA, Wild C. Effects of Water Column Mixing and Stratification on Planktonic Primary Production and Dinitrogen Fixation on a Northern Red Sea Coral Reef. Front Microbiol 2018; 9:2351. [PMID: 30327648 PMCID: PMC6174798 DOI: 10.3389/fmicb.2018.02351] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2018] [Accepted: 09/12/2018] [Indexed: 11/13/2022] Open
Abstract
The northern Red Sea experiences strong annual differences in environmental conditions due to its relative high-latitude location for coral reefs. This allows the study of regulatory effects by key environmental parameters (i.e., temperature, inorganic nutrient, and organic matter concentrations) on reef primary production and dinitrogen (N2) fixation, but related knowledge is scarce. Therefore, this study measured environmental parameters, primary production and N2 fixation of phytoplankton groups in the water overlying a coral reef in the Gulf of Aqaba. To this end, we used a comparative approach between mixed and stratified water column scenarios in a full year of seasonal observations. Findings revealed that inorganic nutrient concentrations were significantly higher in the mixed compared to the stratified period. While gross photosynthesis and N2 fixation rates remained similar, net photosynthesis decreased from mixed to stratified period. Net heterotrophic activity of the planktonic community increased significantly during the stratified compared to the mixed period. While inorganic nitrogen (N) availability was correlated with net photosynthesis over the year, N2 fixation only correlated with N availability during the mixed period. This emphasizes the complexity of planktonic trophodynamics in northern Red Sea coral reefs. Comparing mixed and stratified planktonic N2 fixation rates with those of benthic organisms and substrates revealed a close seasonal activity similarity between free-living pelagic and benthic diazotrophs. During the mixed period, N2 fixation potentially contributed up to 3% of planktonic primary production N demand. This contribution increased by ca. one order of magnitude to 21% during the stratified period. Planktonic N2 fixation is likely a significant N source for phytoplankton to maintain high photosynthesis under oligotrophic conditions in coral reefs, especially during stratified conditions.
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Affiliation(s)
- Arjen Tilstra
- Marine Ecology Department, Faculty of Biology and Chemistry, University of Bremen, Bremen, Germany
| | - Nanne van Hoytema
- Coral Reef Ecology Group, Leibniz Centre for Tropical Marine Research, Bremen, Germany
| | - Ulisse Cardini
- Coral Reef Ecology Group, Leibniz Centre for Tropical Marine Research, Bremen, Germany
- Department of Integrative Marine Ecology, Stazione Zoologica Anton Dohrn, Naples, Italy
| | - Vanessa N. Bednarz
- Coral Reef Ecology Group, Leibniz Centre for Tropical Marine Research, Bremen, Germany
- Centre Scientifique de Monaco, Monaco, Monaco
| | - Laura Rix
- Coral Reef Ecology Group, Leibniz Centre for Tropical Marine Research, Bremen, Germany
- School of Biological Sciences, The University of Queensland, Brisbane, QLD, Australia
| | - Malik S. Naumann
- Marine Ecology Department, Faculty of Biology and Chemistry, University of Bremen, Bremen, Germany
- Coral Reef Ecology Group, Leibniz Centre for Tropical Marine Research, Bremen, Germany
| | | | - Christian Wild
- Marine Ecology Department, Faculty of Biology and Chemistry, University of Bremen, Bremen, Germany
- Coral Reef Ecology Group, Leibniz Centre for Tropical Marine Research, Bremen, Germany
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