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| Djeghri, Nicolas; Stibor, Herwig; Lebeau, Oanez; Pondaven, Philippe. |
| Some jellyfish host zooxanthellae in their tissues (mostly from the family Symbiodiniaceae; Dinophyceae) and supplement their heterotrophic nutrition with their symbiont's photosynthates. The mixotrophy of zooxanthellate jellyfishes (as holobionts) renders the study of their nutrition, growth, and population dynamics complicated. Here, we used an experimental approach to assess how carbon and nitrogen stable isotopes (δ13C and δ15N) as well as the elemental composition (C:N ratios) of zooxanthellate jellyfishes are affected by variations in nutrition sources: i. e. predation (heterotrophic) versus photosynthesis (autotrophic). Our laboratory experiment, conducted on the zooxanthellate jellyfish Cassiopea sp. medusae (including symbionts) in the presence or... |
| Tipo: Text |
Palavras-chave: Stable isotopes; C:N ratios; Photosymbiosis; Mixotrophy; Scyphozoa; Zooxanthellae. |
| Ano: 2020 |
URL: https://archimer.ifremer.fr/doc/00591/70348/68448.pdf |
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| Djeghri, Nicolas; Pondaven, Philippe; Stockenreiter, Maria; Behl, Stephan; Huang, Jessica Y. T.; Hansen, Thomas; Patris, Sharon; Ucharm, Gerda; Stibor, Herwig. |
| Mixotrophic organisms are increasingly recognized as important components of ecosystems, but the factors controlling their nutrition pathways (in particular their autotrophy–heterotrophy balance) are little known. Both autotrophy and heterotrophy are expected to respond to density‐dependent mechanisms but not necessarily in the same direction and/or strength. We hypothesize that the autotrophy–heterotrophy balance of mixotrophic organisms might therefore be a function of population densities. To investigate this relationship, we sampled mixotrophic jellyfish holobionts (host, Mastigias papua etpisoni; symbiont, Cladocopium sp.) in a marine lake (Palau, Micronesia) on six occasions (from 2010 to 2018). Over this period, population densities varied ~100... |
| Tipo: Text |
Palavras-chave: Density dependence; Jellyfish; Marine lakes; Mixotrophy; Stable isotopes; Symbiosis; Zooxanthellae. |
| Ano: 2020 |
URL: https://archimer.ifremer.fr/doc/00663/77469/79159.pdf |
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| Perruche, Coralie; Riviere, Pascal; Pondaven, Philippe; Carton, Xavier. |
| This paper aims at studying analytically the functioning of a very simple ecosystem model with two phytoplankton species. First, using the dynamical system theory, we determine its nonlinear equilibria, their stability and characteristic timescales with a focus on phytoplankton competition. Particular attention is paid to the model sensitivity to parameter change. Then, the influence of vertical mixing and sinking of detritus on the vertically-distributed ecosystem model is investigated. The analytical results reveal a high diversity of ecosystem structures with fixed points and limit cycles that are mainly sensitive to variations of light intensity and total amount of nitrogen matter. The sensitivity to other parameters such as remineralisation, growth... |
| Tipo: Text |
Palavras-chave: Water mixing; Dynamical system; Phytoplankton; Competition; Ecosystem; Modelling. |
| Ano: 2010 |
URL: http://archimer.ifremer.fr/doc/2009/publication-7334.pdf |
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| Coffineau, N.; De La Rocha, C. L.; Pondaven, Philippe. |
| This study presents six new water column profiles of the silicon isotopic composition (delta Si-30) of dissolved silicon (DSi) from the Atlantic and Indian sectors of the Southern Ocean and a variable depth box model of silica cycling in the mixed layer that was constructed to illuminate the evolution of surface ocean delta Si-30 over the full course of a year. In keeping with previous observations, delta Si-30 values ranged from +1.9 to +2.4% in the mixed layer (ML), +1.2 to +1.7 parts per thousand in Winter Water (WW), and +0.9 to +1.4 parts per thousand in Circumpolar Deep Water (CDW). These data also confirmed the occurrence of diminished values for ML delta Si-30 at low DSi concentrations in early austral autumn on the Kerguelen Plateau. The box model... |
| Tipo: Text |
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| Ano: 2014 |
URL: https://archimer.ifremer.fr/doc/00260/37171/35691.pdf |
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| Le Moigne, F. A. C.; Boye, Marie; Masson, A.; Corvaisier, Rudolph; Grossteffan, E.; Gueneugues, A.; Pondaven, Philippe. |
| Meridional and vertical distributions of several biogeochemical parameters were studied along a section in the southeastern Atlantic and the Southern Ocean south of South Africa during the austral summer 2008 of the International Polar Year to characterize the biogeochemical provinces and to assess the seasonal net diatom production. Based on analyses of macro-nutrients, ammonium (NH4), chlorophyll a, (Chl a), phaeopigments, biogenic silica (BSi), particulate inorganic carbon (PIC), and particulate organic carbon and nitrogen (POC and PON, respectively), four biogeochemical domains were distinguished along the section: the subtropical Atlantic, the confluence zone of the subtropical and subantarctic domains, the Polar Frontal Zone (PFZ) in the Antarctic... |
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| Ano: 2013 |
URL: http://archimer.ifremer.fr/doc/00181/29207/27577.pdf |
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| Djeghri, Nicolas; Pondaven, Philippe; Stibor, Herwig; Dawson, Michael N.. |
| Many marine organisms form photosymbioses with zooxanthellae, but some, such as the medusozoans, are less well known. Here, we summarize the current knowledge on the diversity of zooxanthellate jellyfishes, to identify key traits of the holobionts, and to examine the impact of these traits on their ecology. Photosymbiosis with zooxanthellae originated at least seven times independently in Medusozoa; of these, five involve taxa with medusae. While most zooxanthellate jellyfishes are found in clades containing mainly non-zooxanthellate members, the sub-order Kolpophorae (Scyphozoa: Rhizostomeae) is comprised-bar a few intriguing exceptions-of only zooxanthellate jellyfishes. We estimate that 20-25% of Scyphozoa species are zooxanthellate (facultative... |
| Tipo: Text |
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| Ano: 2019 |
URL: https://archimer.ifremer.fr/doc/00604/71661/70246.pdf |
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