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

Auteur(s): Hamdi I., Denis M., Bellaaj-zouari A., Khemakhem H., Hassen M. bel, Hamza A., Barani A., Bezac C., Maalej S.

(Article) Publié: Continental Shelf Research, vol. 93 p.27-38 (2015)


Ref HAL: hal-01436533_v1
DOI: 10.1016/j.csr.2014.10.002
Exporter : BibTex | endNote
Résumé:

TheGulfofGabèsintheEasternMediterraneanBasinisoneofthelargestcontinentalshelvesandisahighlyproductivearea.ThisisincontrasttotheEasternMediterraneanBasinasawholewhichisoligotrophictoultraoligotrophic.Overrecentyears,duetoincreasedpressurefromanthropologicalactivities,therehasbeenadeclineinthebiologicalresourcesintheGulfofGabès.Thishasledscientiststofocustheirresearchon thedifferenttrophiclevelsofthefoodchainandinparticularonphytoplankton.StudiesdedicatedtophytoplanktonintheGulfofGabèshavepreviouslyreliedonconventionalglobalapproaches.Thisworkontheotherhand,examinesultraphytoplankton(o10 mm) distributionatthesinglecelllevelindifferentwatermasses,duringasummercruise(2008).Threedistinctwatermasseswereidentified:modifiedMediterraneanwaters(MMW),modified Atlanticwaters(MAW)andIonianwaters(IW).Despitethesummerperiod,nutrientswereabundantandnon-limiting.Flowcytometryresolved five cellgroups,Prochlorococcus, Synechococcus, picoeukaryotes,nanoeukaryotesandagroupofunidentified cells.Thesecellswerecharacterisedbylow fluorescencesignalsandscattersignalslargerthanthatofcyanobacteriaandpicoeukaryotesandthuswerelabelledLFNanoforlow fluorescencenanoeukaryotes.Theywerefoundinveryhighabundances,whereastheotherusualgroupswererelativelylowinabundancedespitethefavourablegrowthconditions.LFNanofoundduringa2012summercruiseinthesamearea,werealsosorted by flowcytometryandobservedbyscanningelectronmicroscopy.Choanoflagellateswereidentified,andthesenanoflagellatesappeartoaccountforthelowabundanceintheusualultraphytoplanktongroupdue totheirefficientfeeding/grazingmechanism.However,themostabundantLFNanocouldnotbeidentified.Resultsstronglysuggestatop-downcontroloftheecosystem,consistentwiththehighproductivityoftheGulfthatimpliesarapidtransferofmatterandenergytohighertrophiclevels.