Phytoplankton community structure in a high-nutrient, low-chlorophyll region of the eastern Pacific Subantarctic region during winter-mixed and summer-stratified conditions
Résumé
PhytoplanktoncommunitystructurewasanalysedintheSubantarcticsectoroftheeasternSouth Pacific,ahigh-nutrient,low-chlorophyll(HNLC)region,duringaperiodofdeepverticalmixing(austral winterAug-Oct,2005)whenAntarcticIntermediateWater(AAIW)getsformed,andduringaperiodof water-columnstratificationcharacterisedbyshallowmixedlayers(australsummerFeb-Mar,2006). We examinedboththeentirephytoplanktonassemblagethroughtheuseofdiagnosticpigmentsand also thepicophytoplanktonfraction(o3 mm) throughtheuseofclass-specificmolecularprobesand flow cytometry.Boththepigmentandmoleculardatarevealadominanceofprymnesiophytesduringboth the winter-mixedandsummer-stratifiedperiods.Chrysophytesandtheirdiagnosticpigmentswerealso present throughoutmostofthestudyregion.Flowcytometricanalysisrevealedthatthecontributionof photosyntheticpicoeukaryotes(PPEs)tototalpicophytoplankton(PPEsþpicocyanobacteria)abundances increasessystematicallywithincreasinglatitudeanddecreasingtemperature,highlightingtheimportance of PPEsintheSouthernOcean