|   | 
Détails
   web
Enregistrements
Auteur Fouilland, E.; Mostajir, B.; Levasseur, M.; Roy, S.; Vidussi, F.; de Mora, S.; Demers, S.
Titre Effect of mixing on the structure of a natural plankton community: a mesocosm study Type Article scientifique
Année (down) 2016 Publication Revue Abrégée Vie et Milieu
Volume 66 Numéro 3-4 Pages 251-259
Mots-Clés Accumulation; Composition; nitrogen; Phytoplankton Biomass; Phytoplankton Species; Structure Of The Pelagic Food Web; Transport Rates; turbulence; Vertical Mixing
Résumé A plankton community (< 202 μm) from the St. Lawrence Estuary was isolated

in four outdoor mesocosms with SLOW and fast mixing regimes. Variations in the concentrations

of nutrients, chlorophyll a (Chl a), nitrogen transport rates and plankton species composition

were monitored over a 10 day period. The vertical mixing times (Tm) for the slow and

fast mixing regimes were 180 and 60 min, corresponding to a vertical eddy diffusivity (Kv) of

2.34 and 7.03 cm2 s–1, respectively. The different mixing regimes had a strong effect on the

physiology of the phytoplankton and the specific structure of the plankton assemblage. The

Slow mixing regime stimulated the development of a mixed community of flagellates, small

diatoms and proto-metazooplankton while the fast mixing regime triggered the development

of a large diatom-dominated community with lower abundances of proto-metazooplankton. At

the end of the 10 day experiment, the Chl a concentrations were 50 % higher in the mesocosms

with the fast mixing regime than in those with the slow mixing regime. These results indicate

that, under low nutrient conditions, higher turbulence gives a competitive advantage to diatoms

and decreases the zooplankton grazing pressure, resulting in net positive growth. Extrapolation

of these results to natural systems suggests that a wind-driven mixing event may increase

the net phytoplankton biomass production of a stratified water column, even if there is no external

input of nutrients.
Adresse
Auteur institutionnel Thèse
Editeur Lieu de Publication Éditeur
Langue Langue du Résumé Titre Original
Éditeur de collection Titre de collection Titre de collection Abrégé
Volume de collection Numéro de collection Edition
ISSN ISBN Médium
Région Expédition Conférence
Notes Approuvé pas de
Numéro d'Appel MARBEC @ alain.herve @ collection 2082
Lien permanent pour cet enregistrement
 

 
Auteur Cecchi, P.; Garrido, M.; Collos, Y.; Pasqualini, V.
Titre Water flux management and phytoplankton communities in a Mediterranean coastal lagoon. Part II: Mixotrophy of dinoflagellates as an adaptive strategy? Type Article scientifique
Année (down) 2016 Publication Revue Abrégée Marine Pollution Bulletin
Volume 108 Numéro 1–2 Pages 120-133
Mots-Clés Biguglia; Mediterranean coastal lagoon; Mixotrophy; Phyto-PAM; Phytoplankton; Prorocentrum minimum
Résumé Dinoflagellate proliferation is common in coastal waters, and trophic strategies are often advanced to explain the success of these organisms. The Biguglia lagoon is a Mediterranean brackish ecosystem where eutrophication has long been an issue, and where dominance of dinoflagellates has persisted for several years. Monthly monitoring of fluorescence-based properties of phytoplankton communities carried out in 2010 suggested that photosynthesis alone could not support the observed situation all year round. Contrasting food webs developed depending on the hydrological season, with a gradual shift from autotrophy to heterotrophy. Progressively, microphytoplankton assemblages became unequivocally dominated by a Prorocentrum minimum bloom, which exhibited very weak effective photosynthetic performance, whereas paradoxically its theoretical capacities remained fully operational. Different environmental hypotheses explaining this discrepancy were examined, but rejected. We conclude that P. minimum bloom persistence is sustained by mixotrophic strategies, with complex compromises between phototrophy and phagotrophy, as evidenced by fluorescence-based observations.
Adresse
Auteur institutionnel Thèse
Editeur Lieu de Publication Éditeur
Langue Langue du Résumé Titre Original
Éditeur de collection Titre de collection Titre de collection Abrégé
Volume de collection Numéro de collection Edition
ISSN 0025-326x ISBN Médium
Région Expédition Conférence
Notes Approuvé pas de
Numéro d'Appel MARBEC @ isabelle.vidal-ayouba @ collection 1579
Lien permanent pour cet enregistrement
 

 
Auteur Amélineau, F.; Grémillet, D.; Bonnet, D.; Bot, T.L.; Fort, J.
Titre Where to Forage in the Absence of Sea Ice? Bathymetry As a Key Factor for an Arctic Seabird Type Article scientifique
Année (down) 2016 Publication Revue Abrégée Plos One
Volume 11 Numéro 7 Pages e0157764
Mots-Clés Birds; Copepods; Foraging; Predation; Seabirds; Sea ice; Trophic interactions; Zooplankton
Résumé The earth is warming at an alarming rate, especially in the Arctic, where a marked decline in sea ice cover may have far-ranging consequences for endemic species. Little auks, endemic Arctic seabirds, are key bioindicators as they forage in the marginal ice zone and feed preferentially on lipid-rich Arctic copepods and ice-associated amphipods sensitive to the consequences of global warming. We tested how little auks cope with an ice-free foraging environment during the breeding season. To this end, we took advantage of natural variation in sea ice concentration along the east coast of Greenland. We compared foraging and diving behaviour, chick diet and growth and adult body condition between two years, in the presence versus nearby absence of sea ice in the vicinity of their breeding site. Moreover, we sampled zooplankton at sea when sea ice was absent to evaluate prey location and little auk dietary preferences. Little auks foraged in the same areas both years, irrespective of sea ice presence/concentration, and targeted the shelf break and the continental shelf. We confirmed that breeding little auks showed a clear preference for larger copepod species to feed their chick, but caught smaller copepods and nearly no ice-associated amphipod when sea ice was absent. Nevertheless, these dietary changes had no impact on chick growth and adult body condition. Our findings demonstrate the importance of bathymetry for profitable little auk foraging, whatever the sea-ice conditions. Our investigations, along with recent studies, also confirm more flexibility than previously predicted for this key species in a warming Arctic.
Adresse
Auteur institutionnel Thèse
Editeur Lieu de Publication Éditeur
Langue Langue du Résumé Titre Original
Éditeur de collection Titre de collection Titre de collection Abrégé
Volume de collection Numéro de collection Edition
ISSN 1932-6203 ISBN Médium
Région Expédition Conférence
Notes Approuvé pas de
Numéro d'Appel MARBEC @ alain.herve @ collection 1592
Lien permanent pour cet enregistrement
 

 
Auteur Leruste, A.; Malet, N.; Munaron, D.; Derolez, V.; Hatey, E.; Collos, Y.; De Wit, R.; Bec, B.
Titre First steps of ecological restoration in Mediterranean lagoons: Shifts in phytoplankton communities Type Article scientifique
Année (down) 2016 Publication Revue Abrégée Estuarine, Coastal and Shelf Science
Volume 180 Numéro Pages 190-203
Mots-Clés Coastal lagoons; Nutrient; Phytoplankton; Re-oligotrophication; Sewage effluents
Résumé Along the French Mediterranean coast, a complex of eight lagoons underwent intensive eutrophication over four decades, mainly related to nutrient over-enrichment from continuous sewage discharges. The lagoon complex displayed a wide trophic gradient from mesotrophy to hypertrophy and primary production was dominated by phytoplankton communities. In 2005, the implementation of an 11 km offshore outfall system diverted the treated sewage effluents leading to a drastic reduction of anthropogenic inputs of nitrogen and phosphorus into the lagoons. Time series data have been examined from 2000 to 2013 for physical, chemical and biological (phytoplankton) variables of the water column during the summer period. Since 2006, total nitrogen and phosphorus concentrations as well as chlorophyll biomass strongly decreased revealing an improvement in lagoon water quality. In summertime, the decline in phytoplankton biomass was accompanied by shifts in community structure and composition that could be explained by adopting a functional approach by considering the common functional traits of the main algal groups. These phytoplankton communities were dominated by functional groups of small-sized and fast-growing algae (diatoms, cryptophytes and green algae). The trajectories of summer phytoplankton communities displayed a complex response to changing nutrient loads over time. While diatoms were the major group in 2006 in all the lagoons, the summer phytoplankton composition in hypertrophic lagoons has shifted towards green algae, which are particularly well adapted to summertime conditions. All lagoons showed increasing proportion and occurrence of peridinin-rich dinophytes over time, probably related to their capacity for mixotrophy. The diversity patterns were marked by a strong variability in eutrophic and hypertrophic lagoons whereas phytoplankton community structure reached the highest diversity and stability in mesotrophic lagoons. We observe that during the re-oligotrophication process in coastal lagoons, phytoplankton shows complex trajectories with similarities with those observed in freshwater lake systems.
Adresse
Auteur institutionnel Thèse
Editeur Lieu de Publication Éditeur
Langue Langue du Résumé Titre Original
Éditeur de collection Titre de collection Titre de collection Abrégé
Volume de collection Numéro de collection Edition
ISSN 0272-7714 ISBN Médium
Région Expédition Conférence
Notes Approuvé pas de
Numéro d'Appel MARBEC @ alain.herve @ collection 1598
Lien permanent pour cet enregistrement
 

 
Auteur Sebastian, M.; Smith, A.F.; Gonzalez, J.M.; Fredricks, H.F.; Van Mooy, B.; Koblizek, M.; Brandsma, J.; Koster, G.; Mestre, M.; Mostajir, B.; Pitta, P.; Postle, A.D.; Sanchez, P.; Gasol, J.M.; Scanlan, D.J.; Chen, Y.
Titre Lipid remodelling is a widespread strategy in marine heterotrophic bacteria upon phosphorus deficiency Type Article scientifique
Année (down) 2016 Publication Revue Abrégée Isme J.
Volume 10 Numéro 4 Pages 968-978
Mots-Clés 2 enzymes; agrobacterium-tumefaciens; bacterioplankton groups; Ecology; Mediterranean Sea; mesocosm experiment; microbial food-web; north-atlantic ocean; nutrient limitation; phosphate starvation
Résumé Upon phosphorus (P) deficiency, marine phytoplankton reduce their requirements for P by replacing membrane phospholipids with alternative non-phosphorus lipids. It was very recently demonstrated that a SAR11 isolate also shares this capability when phosphate starved in culture. Yet, the extent to which this process occurs in other marine heterotrophic bacteria and in the natural environment is unknown. Here, we demonstrate that the substitution of membrane phospholipids for a variety of non-phosphorus lipids is a conserved response to P deficiency among phylogenetically diverse marine heterotrophic bacteria, including members of the Alphaproteobacteria and Flavobacteria. By deletion mutagenesis and complementation in the model marine bacterium Phaeobacter sp. MED193 and heterologous expression in recombinant Escherichia coli, we confirm the roles of a phospholipase C (PlcP) and a glycosyltransferase in lipid remodelling. Analyses of the Global Ocean Sampling and Tara Oceans metagenome data sets demonstrate that PlcP is particularly abundant in areas characterized by low phosphate concentrations. Furthermore, we show that lipid remodelling occurs seasonally and responds to changing nutrient conditions in natural microbial communities from the Mediterranean Sea. Together, our results point to the key role of lipid substitution as an adaptive strategy enabling heterotrophic bacteria to thrive in the vast P-depleted areas of the ocean.
Adresse
Auteur institutionnel Thèse
Editeur Lieu de Publication Éditeur
Langue English Langue du Résumé Titre Original
Éditeur de collection Titre de collection Titre de collection Abrégé
Volume de collection Numéro de collection Edition
ISSN 1751-7362 ISBN Médium
Région Expédition Conférence
Notes Approuvé pas de
Numéro d'Appel MARBEC @ alain.herve @ collection 1624
Lien permanent pour cet enregistrement