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The characterisation and summer distribution of ultraphytoplankton in the Gulf of Gabes (Eastern Mediterranean Sea, Tunisia) by using flow cytometry

Abstract : TheGulfofGabèsintheEasternMediterraneanBasinisoneofthelargestcontinentalshelvesandisahighly productivearea.ThisisincontrasttotheEasternMediterraneanBasinasawholewhichisoligotrophicto ultraoligotrophic.Overrecentyears,duetoincreasedpressurefromanthropologicalactivities,therehas beenadeclineinthebiologicalresourcesintheGulfofGabès.Thishasledscientiststofocustheirresearch on thedifferenttrophiclevelsofthefoodchainandinparticularonphytoplankton.Studiesdedicatedto phytoplanktonintheGulfofGabèshavepreviouslyreliedonconventionalglobalapproaches.Thisworkon theotherhand,examinesultraphytoplankton(o10 mm) distributionatthesinglecelllevelindifferent watermasses,duringasummercruise(2008).Threedistinctwatermasseswereidentified:modified Mediterraneanwaters(MMW),modified Atlanticwaters(MAW)andIonianwaters(IW).Despitethe summerperiod,nutrientswereabundantandnon-limiting.Flowcytometryresolved five cellgroups, Prochlorococcus, Synechococcus, picoeukaryotes,nanoeukaryotesandagroupofunidentified cells.These cellswerecharacterisedbylow fluorescencesignalsandscattersignalslargerthanthatofcyanobacteriaand picoeukaryotesandthuswerelabelledLFNanoforlow fluorescencenanoeukaryotes.Theywerefoundin veryhighabundances,whereastheotherusualgroupswererelativelylowinabundancedespitethe favourablegrowthconditions.LFNanofoundduringa2012summercruiseinthesamearea,werealso sorted by flowcytometryandobservedbyscanningelectronmicroscopy.Choanoflagellateswereidentified, andthesenanoflagellatesappeartoaccountforthelowabundanceintheusualultraphytoplanktongroup due totheirefficientfeeding/grazingmechanism.However,themostabundantLFNanocouldnotbe identified.Resultsstronglysuggestatop-downcontroloftheecosystem,consistentwiththehigh productivityoftheGulfthatimpliesarapidtransferofmatterandenergytohighertrophiclevels.
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https://hal.archives-ouvertes.fr/hal-01436533
Contributor : Thierry Pin <>
Submitted on : Monday, January 16, 2017 - 3:03:45 PM
Last modification on : Thursday, November 12, 2020 - 3:10:20 PM

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I. Hamdi, Michel Denis, A. Bellaaj-Zouari, H. Khemakhem, M. Bel Hassen, et al.. The characterisation and summer distribution of ultraphytoplankton in the Gulf of Gabes (Eastern Mediterranean Sea, Tunisia) by using flow cytometry. Continental Shelf Research, Elsevier, 2015, 93, pp.27-38. ⟨10.1016/j.csr.2014.10.002⟩. ⟨hal-01436533⟩

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