Plankton Food Web Analysis Of The East China Sea And The Yellow Sea Using Analyses Of Fatty Acids And Stable Isotopes

Zooplankton plays an important role in marine ecosystem by connecting the primary producer and the consumer. Study on food composition of zooplankton provides a way to understand the marine plankton food web and then the energy flux and material cycle in the marine system. In this study, we used fatty acid as indicator for feeding of predators and the carbon and nitrogen stable isotope to analyze the trophic relationships.Theδ13C andδ15N of plankton of 4 size-classes (100μm-200μm; 200μm-500μm; 500-1000μm; 1000μm-2000μm) was analyzed, which were sampled from the East China Sea and the Yellow Sea in November 2009 and June 2010, Theδ¹³C,δ¹⁵N of all size-classes of plankton in 2009 autumn is higher than 2010 spring. Enrichment ofδ¹³C,δ¹⁵N in size-classes of plankton was found to be a positive linear function of organism size. The trophic level of 4 size-classes of plankton calculated from enrichment ofδ15N is also a positive linear function of organism size. Theδ¹³C,δ¹⁵N of all size-classes of plankton displayed a similar spatial distribution pattern reflected in theδ¹³C,δ¹⁵N in Yellow Sea and East China Sea Mixed Water Community are high and the plankton in Yellow Sea Neritic Community and Yellow Sea Central Community are low. Through correlation analysis enrichments of theδ¹³C,δ¹⁵N are found positively correlated with nitrogen and phosphorus nutrients while negatively correlated with salinity in the surface seawaters. The enrichment ofδ13C in Changjiang estuary is relatively high while the enrichment ofδ15N is relatively low.The enrichments ofδ¹³C,δ¹⁵N of 7 dominant zooplankton species of the East China Sea and the Yellow Sea in November 2009 and June 2010 were analyzed, which included one copepod (Calanus sinicus), one krill (Euphausia sp.), one chaetognath (Sagitta sp.), one amphipod(Hyperiidea sp.) and three medusa (Ocyropsis crystalline, Bero cucumis, Liriope tetraphylla). And their trophic level were calculated based on the enrichment ofδ15N. The trophic level of Calanus sinicus and Euphausia sp is relatively low (around 2), which indicates them to be primary consumers, while the trophic level of Sagitta sp. ,Hyperiidea sp. and three medusa is higher.The fatty acid compositions of seston was studied in the the East China Sea and the Yellow Sea in June 2010. The total fatty acid of seston in the East China Sea is higher the in the Yellow Sea. The SDH-2 has higher lipid nutritional values. The fatty acid compositions were also analyzed for the 7 dominant zooplankton species. The copepod, C. sinicus showed a typical herbivorous feeding. Females had a higher content of 16:1ω7 than 18:4ω3, indicating feeding more on diatoms. But copepodites fed more on dinoflagellates in view of the fatty acid 18:4ω3. Sagitta had high contents of 20:1+22:1, reflecting a feeding on herbivorous copepod. And the higher 22:6ω3/20:5ω3 contents also indicated that Sagitta located at relatively high trophic level among studying animals. Hyperiidea sp. had high contents of 20:1+22:1, reflecting a feeding on herbivorous copepod. Euphausia had high contents of PUFA andΣω3 which reflecting their higher lipid nutritional values. In additionally, it has low 22:6ω3/20:5ω3, indicating a lower trophic level in the food web. The total fatty acids of 3 medusa were low, but the higher contents of 20:1+22:1 reflected herbivorous copepods are parts of their food items. High 22:6ω3/20:5ω3 contents also indicated their higher trophic levels. The result ofδ15N and 22:6ω3/20:5ω3 indicate the trophic level in zooplankton are similar. Correlation analysis is made and good positive correlation is found between nitrogen and 22:6ω3/20:5ω3 of the zooplankton.