Aspects of krill growth and condition during late winter-early spring off East Antarctica (110-130°E)

Antarctickrill, Euphausiasuperba, isakeystonespeciesintheSouthernOcean.However,informationon growth,dietandconditionduringwinterandearlyspringislimited,hamperingourunderstandingof these fundamentalbiologicalparametersatthisimportantperiodintheirlifecycle.Ourstudyassessed diet andconditionoflarvalandpostlarvalkrillcollectedfromopenwaterandbelowtheiceoffEast Antarctica(110–130% o E) inSeptember/October2007.Conditionwasassessedusinglipidcontent,growth ratesanddigestiveglandsize;feedinghistorywasassessedusingfattyacidprofilesandstomachcontent analysis;anda207-daystarvationstudyinvestigatedtheresponseofkrilltolong-termfooddeprivation. Potentialfooditems(Calanuspropinquus and sea-icebiota)wereanalysedforlipidandfattyacid compositiontocomparewithkrillsamples.Krillwerefoundtobeingoodcondition,withmeangrowth rate of0.95%permoultforpostlarvaeand14.79%forlarvae,andmeanlipidcontentof24.1%forpostlarvae and 6.6%forlarvae.Fattyacidprofilesandstomachcontentanalysisrevealedtwomainfeedingstrategies - krillbelowtheicewerefeedingmostlyonsea-icediatoms,whilethoseinopenwaterwereingesting copepodsanddetritus.Krillbelowtheicehadlargerdigestiveglandsthanthoseinopenwater.Furciliae fatty acidprofilesindicatedadietofheterotrophicflagellatesand/ordetritus.Postlarvalkrillsurvived207 days offooddeprivationbyusingbodyproteinandlipidreservesforenergy.Incontrast,krillfurciliae were severelydepletedafterjust5daysoffooddeprivation,indicatingthattheymustfeedcontinuallyat this timeofyear.Krill,copepodsandsea-icebiotawerealllowinpolyunsaturatedfattyacids,indicating that krillmustrelyonlaterspringphytoplanktonbloomstoobtaintheseessentialnutrientsrequiredfor reproduction.