Community structure and grazing of the nano-microzooplankton on the continental shelf of the Bay of BiscayReport as inadecuate

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1 LIENSs - LIttoral ENvironnement et Sociétés - UMR 7266 2 MIO - Institut méditerranéen d-océanologie 3 IFREMER - Centre de Brest 4 OOB - Observatoire océanologique de Banyuls 5 LBEM - Laboratoire de Biologie et Environnement Marin

Abstract : In order to investigate the parameters controlling the heterotrophic protists nano-microzooplankton on the continental shelf of the southern Bay of Biscay, plankton communities and their physico-chemical environment were studied 4 times in February, April, June and SeptembereOctober 2004 at three stations in the euphotic zone in the Bay of Biscay. The abundance and carbon biomass of heterotrophic protists ciliates, heterotrophic dinoflagellates and nanoflagellates as well as all the others groups of plankton picoplankton, nanophytoplankton, diatoms, autotrophic dinoflagellates, metazoan micro-zooplankton and mesozooplankton, the environmental parameters and the primary and bacteria production were evaluated at each sampling period. Microzooplankton grazing experiments were undertaken at the same time. Ciliates and heterotrophic dinoflagellates accounted for the main major component of nano-and microzooplankton communities in term of biomass. The total carbon biomass of heterotrophic protists was highest in spring and lowest at the end of summer. The development of heterotrophic protists started after a winter microphytoplankton bloom principally large diatoms, the biomass was lower in June and was low in September through inappropriate prey. The carbon requirement of microzooplankton ranged from 50 to more than 100% of daily primary, bacterial and nanoflagellate production. The heterotrophic protist community was predominantly constrained by bottom-up control in spring and at the end of summer via food availability and quality.

Keywords : heterotrophic protists size-fractionated phytoplankton bacteria mesozooplankton Bay of Biscay environmental factors grazing

Author: Christine Dupuy - Agathe Talarmin - Hans J. Hartmann - Daniel Delmas - C Courties - Elise Marquis -



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