Role of microbial and phytoplanktonic communities in the control of seawater viscosity off West Antarctica (30-80°W).
Résumé
Despitethelong-standingbeliefthatseawaterviscosityisdrivenbytemperatureandsalinity, biologicallyincreasedseawaterviscosityhasrepeatedlybeenreportedinrelationtophytoplankton exudatesinshallow,productivecoastalwaters.Here,seawaterviscositywasinvestigatedinrelationto microbialandphytoplanktoniccommunitiesoffthecoastofEastAntarcticaalonglatitudinaltransects located between301E and801E insub-surfacewatersandatthedeepchlorophyllmaximum(DCM).The physicalcomponentofseawaterviscosityobservedalongeachtransectsrangedfrom1.80to1.95cP, while theactualseawaterviscosityrangedfrom1.85to3.69cP.Thisresultedinbiologicallyincreased seawaterviscosityreachingupto84.9%insub-surfacewatersand77.6%attheDCM.Significantpositive correlationswerefoundbetweenelevatedseawaterviscosityand(i)bacterialabundanceinsub-surface watersand(ii)chlorophyll a concentrationandtheabundanceofflowcytometrically-definedauto-and heterotrophicprotistsattheDCM.Amongthe12groupsand108speciesofprotistsidentifiedunder light microscopy,dinoflagellatesandmorespecifically Alexandriumtamarense and Prorocentrum sp. were themaincontributorstothepatternsobservedforelevatedseawaterviscosity.Ourobservations, which generalisedthelinkpreviouslyidentifiedbetweenseawaterviscosityandphytoplankton compositionandstandingstocktotheSouthernOcean,arethefirstdemonstrationofincreasesin seawaterviscositylinkedtomarinebacterialcommunities,andsuggestthatthemicrobially-increased viscositymightquantitativelybeatleastasimportantastheonerelatedtophytoplanktonsecretion. & 2009 ElsevierLtd.Allrightsreserved