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 mean?¹⁵N value of micro-zooplankton(180-380?m),meso-zooplankton(380-500?m)and macro-zooplankton(>500?m)in summer were 5.34±1.10,5.75±1.16 and 6.58±0.99,and mean?¹⁵N value in winter were 4.64±0.96,5.97±0.52 and 6.48±1.53,respectively.The mean?¹³C value of size fractionated zooplankton in summer were-22.07±0.95,-22.00±0.94 and-22.04±1.13,and mean?¹³C value in winter were-22.13±1.03,-22.31±0.63 and-22.28±1.02,respectively.Significant enrichment of?¹⁵N was found between size fractionated zooplankton groups,while?¹³C showed no significance between three groups.The analysis of common stance showed the mean?¹⁵N 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 mean?¹³C value.The?¹³C and?¹⁵N of all size-classes zooplankton displayed a various spatial distribution pattern.The?¹⁵N 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 the?¹⁵N of size fractionated zooplankton were 5.27-7.01,5.13-7.54 and 5.83-7.99,respectively.The?¹³C 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 the?¹⁵N value of micro-and meso-zooplankton are found positively correlated with zooplankton biomass,while the?¹³C value of all classes zooplankton were positively correlated with logarithm of chlorophyll a.And the?¹⁵N value of macro-zooplankton and the?¹³C value of all classes zooplankton showed no close relationship to zooplankton biomass.The enrichment of?¹³C and?¹⁵N of micro-zooplankton(160-355?m)was analyzed from Daya Bay in August and December,2015.The mean?¹³C 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 mean?¹⁵N value showed no significant differences between summer(8.62±1.96)and winter(7.42±1.18).The?¹³C and?¹⁵N displayed a similar spatial distribution pattern reflected in the?¹³C and?¹⁵N 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 mean?¹³C value showed positively related to surface temperature and salinity.