Food Sources And Sediment Microbial Community Structure In Apostichopus Japonicus Indicated By Fatty Acid Biomarkers Analysis

Food relationship is one of the most basic relationship between biological inecological system. Studies on the food relationship of ecosystem are important tounderstand the matter and energy cycle of the whole system. At present, fatty acidbiomarker is one of the important methods and is widely used in international toresearch food relationship of biological. Compared with the analysis of digestive tractinclusions, fatty acid biomarker method’s advantage is that it can detect the foodanimal ingested recently and actual assimilated. The phospholipid fatty acids areimportant part of living cell membranes and can be synthesized by microbes throughdifferent biochemical pathways.Phospholipid fatty acid composition and content isrelatively stable in intracellular and is easy to extract to qualitativly and quantitativelyresearch, therefore phospholipids fatty acids detected can generally reflect the livingmicroorganism quantity and community structure. Curremtly, research onenvironmental microbial community structure and food sources of sea cucumberunder different culture conditions by using the analysis of fatty acid biomarker is lesscommon at home and abroad. In this study, food sources and fatty acid composition ofA.postichopus japonicus from soil pond and rock pond was comparativly studied andseasonal changes of the sediment microbial community structure in A.postichopusjaponicus was preliminarily analyzed. The results has a certain reference value forparsing the food sources of A.postichopus japonicus and microbial structure in ponds,and is also helpful to further improve the management of sea cucumber farmingtechniques. Specific results are as follows:1. A comparative study of fatty acid composition from soil pond and rock pond inApostichopus japonicusFatty acid composition and changes of soil pond and rock pond in sea cucumber A. japonicus were compared by using the analysis of fatty acid biomarker. The resultsshowed that fatty acid composition and relative contents changed with seasonsobviously in each of the two kinds of ponds.(1)The change rule of fatty acid of thetwo types of ponds were sonsistent in autumn、 winter and spring, that is:polyunsaturated fatty acids (PUFA) contents were found to be highest in winter andspring, next were monounsaturated fatty acids (MUFA) and saturated fatty acids (SFA)respectively. MUFA were higher than PUFA and SFA in spring. However, there weresome differences in the two types of ponds in summer: PUFA contents were higherthan SFA and MUFA in soil pond, while in the rock pond SFA contents were higherthan MUFA and PUFA.(2) The major SFA and MUFA were16:0and16:1n7in allseasons.20:5n3、20:4n6and22:6n3were the main PUFA in all seasons.(3)Theresults also showed1) SFA contents were remarkably different (P<0.01) in all seasonsin the two kinds of ponds and they changed consistently: SFA were the highest insummer, than gradually decreased to a minimum in winter, and slightly elevated inspring;2) there were big difference (P<0.01) in MUFA of the two ponds, MUFA inthe rock pond were lower (P<0.05) than the rock pond in spring and summer, but werejust the opposite in autumn and winter.3) Except spring, PUFA contents weresignificantly different (P<0.01) in other seasons in the two types of ponds. PUFA inthe soil pond were higher (P<0.05) than in the rock pond in summer, then it reservedin autumn and winter.4) The ratios of n-3PUFA/n-6PUFA were among1.15~2.52andit were obviously higher in winter and spring than the other two seasons in both of thetwo ponds. n-3PUFA/n-6PUFA ratios in the soil pond were grately lower (P<0.01)than in the rock pond in winter, and it reserved in spring. There were no significantdifference (P>0.05) in summer and autumn in the two types of ponds.2. A comparative study of food sources from soil pond and rock pond inApostichopus japonicusFood composition and changes of soil pond and rock pond in sea cucumber A.japonicus were compared by using the analysis of fatty acid biomarker. The resultsshowed that:(1) A. japonicus was characterized by significant diatom markers such ashigh ratio of16:1n7/16:0(0.0.66~1.90) and EPA contents (soil pond9.54%~13.37%, rock pond8.44%~15.63%), so diatoms were speculated as one of the main diets. Fattyacid biomarkers specific to bacteria biomarker18:1n7were also found in considerableamounts in the sea cucumber tissue(soil pond5.71%~7.42%, rock pond5.47%~10.98%)，which suggested that there was substantial bacterial input into thefood of the species. The relative contents of brown seaweed biomarker20:4n6werehigh in the year (soil pond6.97%~11.96%，rock pond6.27%~16.24%) with the peakvalues appearing in autumn and winter.(2) The main food sources of the two ponds inA. japonicus changed with seasons. In the soil pond, the main food source of seacucumber in spring indicated big difference among summer、autumn and winter, whilethe latter three seasons was not significant among each other（P>0.05）; in the rockpond, the main food source of sea cucumber was significantly different （P<0.05）among spring, summer and autumn but was not significant（P>0.05）between autumnand winter.(3) Contributions of food sources were remarkably different in the twoponds:20:5n3fatty acids, besides of summer was significantly higher in rock pondthan in soil pond in other seasons （P<0.05）;20:4n6fatty acids were significantlyhigher in rock pond in autumn and winter, while18:1n7fatty acids were significantlylower in rock pond in summer and autumn..(4) Overall comparison between the twotypes of ponds, the major food source of sea cucumber showed significant differencebetween summer and winter, while similarity between spring and autumn; seasonalfluctuations of sea cucumber food composition is bigger in critical cofferdamaquaculture pond than in soil pond.3. Study on seasonal changes of the sediment microbial community structure inApostichopus japonicusPhospholipid fatty acid(PLFA) composition and seasonal changes of the sedimentmicrobial community structure in sea cucumber A. japonicus were researched byusing phospholipid fatty acid (PLFA) analysis. The results showed that the sedimentPLFAs were mainly contributed by the saturated fatty acid，branched fatty acid andmonounsaturated fatty acid; the amount of cyclopropane fatty acid was relativelysmaller. The content of cy17:0were higher in summer and winter while minimum inautumn. The majority of microorganisms in the sediment were bacteria during the period and bacteria abundance were highest in summer, lowest in spring;However,the proportion of the bacterial biomass in the microbial community werehighest in autumn, lowest in winter. G+bacterium biomass predominated within thebacteria structure. It is more suitable for G+bacterium grew in spring while G－bacterium in summer. With the breeding going on, the sediment ecological systembecame more stable in later period.