High density of ice krill (Euphausia crystallorophias) in the Amundsen sea coastal polynya, Antarctica

Abstract

High densitiesoficekrill Euphausia crystallorophias wereobservedalongsixacoustictransectswithin the AmundsenSeaCoastalPolynya,Antarctica.Two-frequencyacousticbackscatterdatawasexamined in theaustralsummersofJanuary2011andFebruary2012.AdBidentification window(Sv120 38) identified icekrilldominatingtheacousticbackscatter.Thedensityoficekrill,calculatedwiththe stochastic distorted-wavebornapproximationmodel,rangedbetween4.5and30gwetmassm 2 for each transect(ameanof16gwetmassm 2 for alltransects),thesehighvaluesareanorderof magnitude higherthanrecordedpreviouslyintheRossSeaPolynya.Highdensitiesweredetectedalong the iceshelfandneartheboundarybetweenpackiceandcoastalpolynya,andwepostulatethatthese could beimportanthabitatsforicekrill.Thehighdensitiesobservedalongthetransectsmakeicekrilla potentiallyimportant,butpoorlyknowncontributortothesehigh-latitudeshelffoodwebs.