LEMAR UMR6539

Plouzané, France

LEMAR UMR6539

Plouzané, France

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Menkes C.E.,University of New Caledonia | Allain V.,British Petroleum | Rodier M.,IRD Montpellier | Gallois F.,Institute Of Recherche Pour Le Developpement | And 14 more authors.
Deep-Sea Research Part II: Topical Studies in Oceanography | Year: 2015

Tuna catches represent a major economic and food source in the Pacific Ocean, yet are highly variable. This variability in tuna catches remains poorly explained. The relationships between the distributions of tuna and their forage (micronekton) have been mostly derived from model estimates. Observations of micronekton and other mid-trophic level organisms, and their link to regional oceanography, however are scarce and constitute an important gap in our knowledge and understanding of the dynamics of pelagic ecosystems. To fill this gap, we conducted two multidisciplinary cruises (Nectalis1 and Nectalis2) in the New Caledonian Exclusive Economic Zone (EEZ) at the southeastern edge the Coral Sea, in 2011 to characterize the oceanography of the region during the cool (August) and the hot (December) seasons. The physical and biological environments were described by hydrology, nutrients and phytoplankton size structure and biomass. Zooplankton biomass was estimated from net sampling and acoustics and micronecton was estimated from net sampling, the SEAPODYM ecosystem model, a dedicated echosounder and non-dedicated acoustics. Results demonstrated that New Caledonia is located in an oligotrophic area characterized by low nutrient and low primary production which is dominated by a high percentage of picoplankton cyanobacteria Prochlorococcus (>90%). The area exhibits a large-scale north-south temperature and salinity gradient. The northern area is influenced by the equatorial Warm Pool and the South Pacific Convergence Zone and is characterized by higher temperature, lower salinity, lower primary production and micronekton biomass. The southern area is influenced by the Tasman Sea and is characterized by cooler temperature, higher salinity, higher primary production and micronekton biomass. The dynamic oceanography and the complex topography create a myriad of mesoscale features including eddies, inducing patchy structures in the ecosystem. During the cool season, a tight coupling existed between the ocean dynamics and primary production, while there was a stronger decoupling during the hot season. There was little difference in the composition of mid-trophic level organisms (zooplankton and micronekton) between the two seasons. This may be due to different turn-over times and delays in the transmission of primary production to upper trophic levels. Examination of various sampling gears for zooplankton and micronekton showed that net biomass estimates and acoustic-derived estimates compared reasonably well. Estimates of micronekton from net observations and the SEAPODYM model were in the same range. The non-dedicated acoustics adequately reproduced trends observed in zooplankton from nets, but the acoustics could not differentiate between zooplankton and micronekton and absolute biomasses could not be calculated. Understanding the impact of mesoscale features on higher trophic levels will require further investigation and patchiness induced by eddies raises the question of how to best sample highly dynamic areas via sea experiments. © 2014 Elsevier Ltd.


Diatoms of the genus Pseudo-nitzschia are potentially toxic microalgae, whose blooms can trigger amnesic shellfish poisoning. The purpose of this study was to test and adapt different probes and procedures in order to assess the physiological status of Pseudo-nitzschia multiseries at the cell level using flow cytometry. To perform these analyses, probes and procedures were first optimized for concentration and incubation time. The percentage of dead Pseudo-nitzschia cells, the metabolic activity of live cells and their intracellular lipid content were then measured following a complete growth cycle. In addition, chlorophyll autofluorescence and efficiency of photosynthesis (quantum yield) were monitored. The concentration and viability of bacteria present in the medium were also assessed. Domoic acid (DA) was quantified as well. Just before the exponential phase, cells exhibited high metabolic activity, but low DA content. DA content per cell became most abundant at the beginning of the exponential phase when lipid storage was high, which provided a metabolic energy source, and when they were surrounded by a high number of bacteria (high bacteria/P. multiseries ratio). These physiological measurements tended to decrease during exponential phase and until stationary phase, at which time P. multiseries cells did not contain any DA nor store any lipids, and started to die. Copyright © 2011 Institut Pasteur. Published by Elsevier Masson SAS. All rights reserved.


Lelong A.,LEMAR UMR6539 | Hegaret H.,LEMAR UMR6539 | Soudant P.,LEMAR UMR6539
Research in Microbiology | Year: 2011

Diatoms of the genus Pseudo-nitzschia are potentially toxic microalgae, whose blooms can trigger amnesic shellfish poisoning. The purpose of this study was to test and adapt different probes and procedures in order to assess the physiological status of Pseudo-nitzschia multiseries at the cell level using flow cytometry. To perform these analyses, probes and procedures were first optimized for concentration and incubation time. The percentage of dead Pseudo-nitzschia cells, the metabolic activity of live cells and their intracellular lipid content were then measured following a complete growth cycle. In addition, chlorophyll autofluorescence and efficiency of photosynthesis (quantum yield) were monitored. The concentration and viability of bacteria present in the medium were also assessed. Domoic acid (DA) was quantified as well. Just before the exponential phase, cells exhibited high metabolic activity, but low DA content. DA content per cell became most abundant at the beginning of the exponential phase when lipid storage was high, which provided a metabolic energy source, and when they were surrounded by a high number of bacteria (high bacteria/. P. multiseries ratio). These physiological measurements tended to decrease during exponential phase and until stationary phase, at which time P. multiseries cells did not contain any DA nor store any lipids, and started to die. © 2011 Institut Pasteur.


PubMed | LEMAR UMR6539
Type: | Journal: Methods in molecular biology (Clifton, N.J.) | Year: 2015

The interest in the physiological roles and bioactivities of plant phenols has increased over the past decades. In seaweeds, many investigations have dealt with phenolic compounds of Phaeophyceae (phlorotannins), even though little is known so far about the ecophysiological variations of their pool or their biosynthetic pathways. We describe here a simple procedure based on the use of water-organic solvent mixtures for the extraction of phlorotannins. Crude extracts are semi-purified and fractionated by separating methods based on both the polarity and the molecular size of compounds. Phenols are then quantified by the Folin-Ciocalteu method and their radical-scavenging activity is characterized using the DPPH test. All along the purification process of phenolic compounds, the efficiency of separation is assessed by (1)H-NMR.


PubMed | LEMAR UMR6539
Type: Journal Article | Journal: Research in microbiology | Year: 2011

Diatoms of the genus Pseudo-nitzschia are potentially toxic microalgae, whose blooms can trigger amnesic shellfish poisoning. The purpose of this study was to test and adapt different probes and procedures in order to assess the physiological status of Pseudo-nitzschia multiseries at the cell level using flow cytometry. To perform these analyses, probes and procedures were first optimized for concentration and incubation time. The percentage of dead Pseudo-nitzschia cells, the metabolic activity of live cells and their intracellular lipid content were then measured following a complete growth cycle. In addition, chlorophyll autofluorescence and efficiency of photosynthesis (quantum yield) were monitored. The concentration and viability of bacteria present in the medium were also assessed. Domoic acid (DA) was quantified as well. Just before the exponential phase, cells exhibited high metabolic activity, but low DA content. DA content per cell became most abundant at the beginning of the exponential phase when lipid storage was high, which provided a metabolic energy source, and when they were surrounded by a high number of bacteria (high bacteria/P. multiseries ratio). These physiological measurements tended to decrease during exponential phase and until stationary phase, at which time P. multiseries cells did not contain any DA nor store any lipids, and started to die.

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