Preliminary Study On Stable Carbon And Nitrogen Isotope Of Zooplankton In The Northern South China Sea And Adjacent Waters

Zooplankton plays an important role in marine food web by connecting the microbial loop and classic food chain.Study on food composition of zooplankton provides a way to understand the material cycle and energy flux in marine ecosystem.As the largest marginal sea in China,the South China Sea has a wide continental shelf with input of the Pearl River in west,and the Luzon Strait was the only deeply channel for water exchange between South China Sea and ocean.Daya Bay,is one of the largest semi-closed bays along the coast of South China Sea,and was suffering from the influence of various anthropogenic activities.In summer and winter 2015,we used the nitrogen and carbon stable isotope to analyze the food composition of zooplankton.The purpose of this research is to provide fundamental information for research the marine ecosystem in South China Sea.The carbon and nitrogen stable isotope of zooplankton was analyzed,which were sampled from the northern South China Sea in August and December,2015.The meanδ¹⁵N value of micro-zooplankton（180-380μm）,meso-zooplankton（380-500μm）and macro-zooplankton（>500μm）in summer were 5.34±1.10,5.75±1.16 and 6.58±0.99,and meanδ¹⁵N value in winter were 4.64±0.96,5.97±0.52 and 6.48±1.53,respectively.The meanδ¹³C value of size fractionated zooplankton in summer were-22.07±0.95,-22.00±0.94 and-22.04±1.13,and meanδ¹³C value in winter were-22.13±1.03,-22.31±0.63 and-22.28±1.02,respectively.Significant enrichment ofδ¹⁵N was found between size fractionated zooplankton groups,whileδ¹³C showed no significance between three groups.The analysis of common stance showed the meanδ¹⁵N value of zooplankton in summer was higher than that in winter,especially the micro-zooplankton（P<0.01）,and no significant seasonal differences of the meanδ¹³C value.Theδ¹³C andδ¹⁵N of all size-classes zooplankton displayed a various spatial distribution pattern.Theδ¹⁵N and biomass of zooplankton in the areas of Pearl River estuary,Dongsha islands and southern Taiwan Strait were high.And in this areas,the ranges of biomass were 6.57-13.62mg·m^-3,and theδ¹⁵N of size fractionated zooplankton were 5.27-7.01,5.13-7.54 and 5.83-7.99,respectively.Theδ¹³C of zooplankton in the northern stations were high in winter,may be associated to upwelling of northeast of the South China Sea.Through correlation analysis theδ¹⁵N value of micro-and meso-zooplankton are found positively correlated with zooplankton biomass,while theδ¹³C value of all classes zooplankton were positively correlated with logarithm of chlorophyll a.And theδ¹⁵N value of macro-zooplankton and theδ¹³C value of all classes zooplankton showed no close relationship to zooplankton biomass.The enrichment ofδ¹³C andδ¹⁵N of micro-zooplankton（160-355μm）was analyzed from Daya Bay in August and December,2015.The meanδ¹³C value of micro-zooplankton in summer（-16.97±1.31）were high than that in winter（-21.21±1.74）（P<0.01）,and the meanδ¹⁵N value showed no significant differences between summer（8.62±1.96）and winter（7.42±1.18）.Theδ¹³C andδ¹⁵N displayed a similar spatial distribution pattern reflected in theδ¹³C andδ¹⁵N in the port area,marine cage-culture area and outflow of nuclear power plant were high and were low in the center,mouth and outside of Daya Bay.Correlation analysis showed that the meanδ¹³C value showed positively related to surface temperature and salinity.