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Auteur (up) 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 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.
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Numéro d'Appel MARBEC @ alain.herve @ collection 2082
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Auteur (up) Laanaia, N., Vaquer, A., Fiandrino, A., Genovesi, B., Pastoureaud, A., Cecchi, P., Collos, Y.
Titre Wind and temperature controls on Alexandrium blooms (2000-2007) in Thau Lagoon (Western Mediterranean) Type Article scientifique
Année 2013 Publication Revue Abrégée Harmful Algae
Volume 28 Numéro Pages 31-36
Mots-Clés alexandrium catenella/tamarense; catenella; dinoflagellate; dinophyceae; dynamics; growth; harmful; mediterranean; resting cysts; sea water; small-scale turbulence; southern france; sst; thau lagoon; wind stress
Résumé Since 1998, blooms of Alexandrium catenella/tamarense in the lagoon of Thau developed regularly each autumn, reaching a maximum of several millions cells per liter in 2004. By contrast, spring blooms occurred only twice (in 2000 and 2007). During these periods, sea surface temperatures (SST) and the wind patterns appear to impact the bloom occurrences much more than the apparent limiting resources such as inorganic nutrients. The analysis of SST and wind from April to June and September to November (from 2000 to 2007) indicates first that there has to be an initial wind stress in order to resuspend the cysts buried in the sediment. Blooms then occur after a period of weak winds (<4 m s(-1)) and of stable SST close to 20 degrees C (+/- 2 degrees C). Those conditions appear to be most favorable for germination of Alexandrium cysts and its ensuing vegetative growth. This period of stability (a few days to a few weeks) allows the development of the inoculum from the cyst's germination, its cohesion because of reduced hydrodynamics, and development of vegetative cells that are sensitive to agitation. Strong winds during 1-2 day periods can interrupt the bloom dynamics by dispersing (advection due to southeasterly winds) and/or eliminating (turbulence due to northwesterly winds) the vegetative cells. In the spring, under the same conditions of optimal SST, strong wind episodes dominate and those, as well as biological factors very likely lead to a lower occurrence of blooms relative to the fall situation. (C) 2013 Elsevier B.V. All rights reserved.
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Langue English Langue du Résumé Titre Original
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Volume de collection Numéro de collection Edition
ISSN 1568-9883 ISBN Médium
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Numéro d'Appel MARBEC @ isabelle.vidal-ayouba @ collection 939
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