Characterization of Coolia spp. (Gonyaucales, Dinophyceae) from Southern Tunisia: first record of Coolia malayensis in the Mediterranean Sea.

This study provides the first report of the presence of Coolia malayensis in the Mediterranean Sea, co-occurring with C. monotis. Isolated strains from the Gulf of Gabes, Tunisia (South-eastern Mediterranean) were identified by morpho-logical characterization and phylogenetic analysis. Examination by light and scanning electron microscopy revealed no significant morphological differences between the Tunisian isolates and other geographically distant strains of C. monotis and C. malayensis. Phylogenetic trees based on ITS1-5.8S-ITS2 and D1-D3/28S rDNA sequences showed that C. monotis strains clustered with others from the Mediterranean and Atlantic whereas the C. malayensis isolate branched with isolates from the Pacific and the Atlantic, therefore revealing no geographical trend among C. monotis and C. ma-layensis populations. Ultrastructural analyses by transmission electron microscopy revealed the presence of numerous vesicles containing spirally coiled fibers in both C. malayensis and C. monotis cells, which we speculate to be involved in mucus production

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

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

Seasonal variability of picophytoplankton under contrasting environments in northern Tunisian coasts, southwestern Mediterranean Sea

We investigated at the single cell level during 16 months (June 2012 to September 2013) the temporal distribution of picophytoplankton (picoeukaryotes, Synechococcus and Prochlorococcus) communities in two contrasted ecosystems: the Bay of Bizerte characterised by an oligotrophic regime typical of the Mediterranean Sea and the Bizerte Lagoon that exhibits a mesotrophic/eutrophic state. We aimed at depicting seasonal variations and quantifying the relationships between the environmental factors and the structure and abundance of picophytoplankton communities. Results showed that picophytoplankton groups were able to grow under a wide range of environmental conditions varying seasonally, although their abundances and contributions to the total chlorophyll biomass significantly varied and showed importance in the Bay of Bizerte. Synechococcus was the most abundant group reaching 225 * 10(3) cells.cm(-3) in the Bay and 278 * 10(3) cells.cm(-3) in the lagoon. This group was present all over the year in both ecosystems. Structural equation model results pointed out a different configuration regarding the picophytoplankton environmental drivers. The complexity of the configuration, i.e. number of significant links within the system, decreased under enhanced eutrophication conditions. The less exposure to anthropogenic stress, i.e. in the Bay of Bizerte, highlight a larger role of nutrient and hydrological conditions on the seasonal variations of picophytoplankton, whereas a negative effect of eutrophication on picophytoplankton communities was unveiled in the Bizerte Lagoon. We stress that such influence may be exacerbated under expected scenarios of Mediterranean warming conditions and nutrient release in coastal ecosystems

Seasonal variability of picophytoplankton under contrasting environments in northern Tunisian coasts, southwestern Mediterranean Sea

Highlights: • Picophytoplankton was able to grow under a wide range of environmental conditions varying seasonally. • Picophytoplankton variability was more marked in the bay than in the lagoon. • Picophytoplankton decreased in the lagoon under enhanced anthropogenic stress. • Synechococcus, the most abundant group of the community, was frequently present in both ecosystems during the monitoring. We investigated at the single cell level during 16months (June 2012 to September 2013) the temporal distribution of picophytoplankton (picoeukaryotes, Synechococcus and Prochlorococcus) communities in two contrasted ecosystems: the Bay of Bizerte characterised by an oligotrophic regime typical of the Mediterranean Sea and the Bizerte Lagoon that exhibits a mesotrophic/eutrophic state. We aimed at depicting seasonal variations and quantifying the relationships between the environmental factors and the structure and abundance of picophytoplankton communities. Results showed that picophytoplankton groups were able to grow under a wide range of environmental conditions varying seasonally, although their abundances and contributions to the total chlorophyll biomass significantly varied and showed importance in the Bay of Bizerte. Synechococcus was the most abundant group reaching 225*103 cells·cm-3 in the Bay and 278*103 cells·cm-3 in the lagoon. This group was present all over the year in both ecosystems. Structural equation model results pointed out a different configuration regarding the picophytoplankton environmental drivers. The complexity of the configuration, i.e. number of significant links within the system, decreased under enhanced eutrophication conditions. The less exposure to anthropogenic stress, i.e. in the Bay of Bizerte, highlight a larger role of nutrient and hydrological conditions on the seasonal variations of picophytoplankton, whereas a negative effect of eutrophication on picophytoplankton communities was unveiled in the Bizerte Lagoon. We stress that such influence may be exacerbated under expected scenarios of Mediterranean warming conditions and nutrient release in coastal ecosystems