Lipid Content And Composition Of Calanus Sinicus And Its Ecological Function During Oversummering In The Southern Yellow Sea

As one of the important biological macromolecules, lipids play an importantrole in crucial period of zooplankton life-history like diapause, reproduction andontogeny. However, as an ecologically important copepod species in the shelf watersof the North-west Pacific Ocean, there are few studies concern the lipid of Calanussinicus. The present research studied the lipid content and compositions, as well asthe role of lipid, in Calanus sinicus in the sourthern Yellow Sea.First, we studied the the lipid content and compositions of Calanus sinicus.Samples of Calanus sinicus in different development stages (CIII to Adult) werecollected from the Southern Yellow Sea in spring (April,2011). The results showthat the major lipid components were wax ester and phospholipid, and they togethercontributed about90%to total lipid, while triglyceride accounted for only6%. TheCIII copepodite has been started to accumulate wax ester and CV copepodite shownthe highest content in all development stages. The fatty acid compositions wereanalyzed for the two major lipid classes, wax ester and phospholipid. For wax ester,the dominate fatty acids were14:0,16:0,16:1ω7,18:1ω9,18:4ω3,20:1ω9,20:5ω3,22:1ω11and22:6ω3. For phospholipid, the dominate fatty acids were14:0,16:0,18:0,18:1ω9,18:4ω3,20:5ω3and22:6ω3. The fatty acid compositions ofwax ester and phospholipid show great differences. The fatty acids of wax ester has ahigh percentage of moneunstaturated fatty acis (MUFA) while phospholipid show ahigh content of polyunsaturated fatty acids (PUFA), with the percentage of more than50%.Second, the roles of the major lipid classes were studied via in situ collectedsamples. We collected samples from the Southern Yellow Sea in autumn (November,2010) and spring (April,2011). The results show that the total lipid content of femaleC. sinicus was about10.6%~12%of dry body mass, while C5stage in spring had ahigher percentage, about17%of dry mass. The role of different lipid classes wasdiscussed as follows:(1) Wax ester served as an important energy deposit. Thefluctuated wax ester content of C. sinicus suggested the different strategies in energyneeds and utilization of different development stages and seasons.(2) Thecoincidence of active reproduction and high content of phospholipid in femaleindicated that phospholipid plays an important role in the egg production of C.sinicus.(3) The composition of TAG was relatively lower than that of wax ester andphospholipid in C. sinicus, but it might work in the transformation of different lipidclasses.Last, as over-summering is important for C. sinicus, we studied the dynamics ofdifferent lipid classes and FAs and their functions during this period. In August2011,the most abundant of C. sinicus was found at the certain regions in the Yellow SeaCold Bottom Waters (YSCBW, water temperature <10oC, ranging from93.3ind/m3to446.9ind/m3, mean,242.6ind/m3). The area near the shore of the East China Seaalso showed an abundant C. sinicus population (range,60.8–148.4ind/m3; mean,91.0ind/m3). The lipid content of C5in the YSCBW was43.1μg/ind, while the lipidcontent of the females in the YSCBW (mean,24.6μg/ind) and at the area near theshore of the East China Sea (mean,18.2μg/ind) was lower than C5in YSCBW. TheC5in the YSCBW can use stored lipid and sustain on a limited food supply duringover-summering, while C. sinicus in other areas require active feeding to surviveduring the summer. To further our understand of lipid dynamics duringover-summering, lipids and FAs of were analysied for samples which were got at thecentral part of Southern Yellow Sea in June, August, and November which areconsidered as the pre-, during-and end-diapause period. The results show that C. sinicus store up lipids (mainly wax ester and phospholipid) against summer. Theyconsumed most of the stored lipid, even some phospholipid, for energy needs duringthe over-summering period. This is different from Calanus spp. in high latitudewhich uses most of their storage lipids for ascent or reproduction needs. In addition,although polyunsaturated fatty acids (PUFA) in wax ester exhibited a selectivelyutilization, this selection was unrelated to diapause termination. What is the functionof this selection need further studies.