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Study On The Trophic Relationships In The Yellow Sea Ecosystem Using Fatty Acid Markers

Posted on:2011-01-21Degree:DoctorType:Dissertation
Country:ChinaCandidate:M T LiuFull Text:PDF
GTID:1100330332996950Subject:Marine Ecology
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As one of the important biological macromolecules, fatty acid plays verymportant roles in marine organisms. Besides, fatty acid could also be used as markersto indicate the feeding of predators. Fatty acid features of diatoms and dinoflagellateswere analyzed. Subsequently, feeding experiment was carried out with the copepodCalauus siuicus using unialgae as diets to verify the validity of fatty acid as markers.Fatty acid markers were then employed in the study of the trophic relationships inJiaozhou Bay and southern Yellow Sea.The fatty acid compositions were analyzed for Scrippsiella trochoidea,Proroceutruin inicaus, Skeletoueina costatuin and Chaetoceros sp二For S. trochoideaand P. micaus, the dominance of 16:0, 18:4c}3, 18:Sc}3, 20:3c}6, 22:6c}3 indicated atypical fatty acid composition of dinoflagellates. For S. costatmn and Chaetoceros sp.,the dominant fatty acids were 14:0,16:0,16:1c}7,20:Sc}3, suggesting a diatom feature.Although the incorporation and turnover rates of dietary fatty acids were differentfrom each other, the feeding experiment could still provide clear evidence for thepotential of specific fatty acids as trophic markers. Polyunsaturated fatty acids whichcannot be synthesized by copepods decreased obviously during the starvationexperiment, while structural fatty acids with more conservative chemical propertieswere consumed in a lesser degree. 18:4c}3, 22:6c}3, 18:4c}3/16:1c}7,∑18/∑16 and22:6w3/20:Sw3 increased in different degrees at the end of the feeding experimentwhen Calauus siuicus was offered with P. micaus. However, the structural fatty acid22:6c}3 was not a suitable marker to indicate the ingestion of dinoflagellate. When thecopepod was fed with S. costatmn, only 22:603 and 16:10}7/18:40}3 increased at the end of the experiment. Based on overall considerations of the variations of these fattymarkers and the Pearson correlation analysis, we deemed that 18:4c}318:4c}3/16:1c}7 and∑18/∑16 were useful markers to reflect the ingestion of P. micausby C. siuicus, and only 16:1c}7/18:4c}3 could be used as marker for the ingestion of S.costatu}n.Seston and the copepod C. siuicus were investigated in Jiaozhou Bay annually inview of their fatty acid compositions. We aimed at elucidating the trophicrelationships between seston and the copepod by depicting the spatial and temporalvariations of their fatty acid compositions. Total fatty acid and Chl a correlatedsignificantly with each other, indicating that phytoplankton was an important sestoncomponents. But it seemed that other particles such as organic detritus, ciliates andbacteria might also contribute a surprising proportion. Principal component analysiswas carried out in this study to ordinate the seston according to stations and months.The results showed that diatom contributed a larger proportion to the northeast ofJiaozhou Bay (AS) than in the middle (C3) and out of the bay (D7). In view of lipidnutrients, seston in the northeast of Jiaozhou Bay showed higher food quality than theother areas. In July 2008, station AS and C3 were different from other cases by higherpercentage of dinoflagellates markers and lipid nutrients. C. siuicus showed atime-delayed response to the spring algae bloom. The essential fatty acids 20:Sc}3 and22:603 were found to occupy a proportion over 50% in C. siuicus, which wassignificantly higher than the polar copepods. 16:1c}7, 18:4c}3 and themonounsaturates 20:1 and 22:1 in C. siuicus verified the herbivorous feeding of thiscopepod. But the comparatively low levels of these fatty acids compared to their polarcounterparts allowed the conclusion to be drawn that besides phytoplankton, C.siuicus might feed on a wider range of particles including organic detritus, eggs,bacteria, small copepods and ciliates, etc.Fatty acid compositions of seston and C. siuicus were analyzed in the southernYellow Sea in December 2006, March, May and August 2007. Total fatty acid, diatommarkers, dinoflagellates markers, PUFA and∑c}3 fatty acid of seston exhibited similar temporal and spatial distributions in the southern Yellow Sea. Phytoplanktonprospered in spring, followed by the increase of these markers in March and May,indicating higher lipid nutrients in this season. The center of the research area showedconsistent low levels of there fatty acid markers all the year around, indicating acomparatively low levels of phytoplankton and lipid nutritional value. Compared toJiaozhou Bay, C. siuicus in the southern Yellow Sea showed comparatively low levelsof PUFA and c}}3 (especially 20:Sc}}3 and 22:6c}}3) and high levels of 20:1 and 22:1,indicating a more herbivorous feeding in this region. The egg production rates offemale C. siuicus showed positively correlations with 16:1c}7,∑16 and 20:Sc}3.Thepresence of these diatom markers suggested the important roles diatom played in thereproduction of C. siuicus.Fatty acid composition of seston in June 2009 displayed a similar spatialdistribution pattern with the cruises conducted in 2006 and 2007. C04 and B18 weredistinguished from other stations by the obvious phytoplankton markers and higherlipid nutritional values. Female and copepodid of C. siuicus showed a typicalherbivorous feeding. But the significantly higher content of 20:1+22:1 in copepodidindicated that copepodid seemed to feed on phytoplankton at a higher level. Besides,copepodid of C. siuicus might feed preferentially on dinoflagellates in view of thefatty acid 18:4c}3.Euphausia pacifica has a higher content of 18:403 than 16:107,indicating a preferential feeding on dinoflagellates. Sagitta was characteristic of highcontent of 22:6c}}3, indicating a higher trophic level in zooplankton. Hyperiidea in thepresent stu勿showed high contents of 16:1c}7, 18:4c}3 and 20:1+22:1,we inferredthat this Amphipoda mainly fed on herbivorous copepod. Stomolophus meleagrisexhibited a distinct feature of feeding on detritus. Generally, C. siuicus, Euphausiapacifica and Hyperiidea might have higher lipid nutritional values for the predators.Principal component analysis was also employed in predators in higher trophic levels.Benthic species such as Phili}te sp., Charybdis japo}tica and Cra}tgo}t affi}tisdistributed away from other species by their obvious fatty acid features of detritus,which might be derived from the direct ingestion of detritus or the feeding on benthic organisms. Pseudosciaeua polyactis, Astrocouger myriaster, Setipiuua taty andCollichthys uiveatus which showed higher contents of phytoplankton grouped together,markers andlipid nutritional values for upper predators could be these speciesshowed higher absorption and transformation rates of dietary fatty acids and fed onherbivorous organisms directly or indirectly.This paper aims at demonstrating the trophic relationships in Yellow Sea in a fattyacid approach. In fact, it is more complex to use this technique in moderate regionsthan in polar areas for the more complex and differing environment. To a betterunderstanding of the trophic linkages in moderate marine environment, we adviseother techniques such as stable isotope analysis also be employed.
Keywords/Search Tags:fatty acid, trophic relationship, biomarker
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