The Study Of Microzooplankton Grazing In The Eastern Indian Ocean And South China Sea

The dilution method was used to conduct field studies in the Bay of Bengal(23 stations)in the eastern Indian Ocean,the central and northern South China Sea(21 stations)and the western South China Sea(23 stations)from 2016 to 2017.The main results are as follows:1.The average abundance of surface phytoplankton were 7.85×103 cells·L-1,4.87×103 cells·L-1 and 4.78×103 cells·L-1 in the eastern Indian Ocean(EIO)during autumn in 2016,the central and northern South China Sea(SCS)during spring in 2017 and the western SCS during autumn in 2017,respectively.The abundance of phytoplankton were mainly contributed by diatoms and dinoflagellates(except for Trichodesmium thiebautii)and abundance of Trichodesmium thiebautii were abnormally high in some sites.In the EIO,the high abundances of phytoplankton were located at Site S06 affected by diluting water and Site SO 1-17 affected by upwelling.In the SCS the phytoplankton distribution in the surface was correlated with the chlorophyll a(Chl a)concentration.The abundance of phytoplankton in the northern SCS was significantly higher than that in the central SCS.2.During the spring and autumn of 2017,the abundances of surface microzooplankton in the SCS were 101-374 ind·L-1(199 ind·L-1 for average)and 136-782 ind·L-1(467 ind·L-1 for average),respectively.The abundance compositions of the four types microzooplankton were quite different.For the central and northern SCS,ciliates were the the most dominant microzooplankton species,while the abundance of heterotrophic dinoflagellates was higher than that of ciliates.Both the abundances of ciliates and heterotrophic dinoflagellates were significantly correlated with surface temperature.In the western SCS,the contribution of microzooplankton abundance was mainly made by aloricate ciliates,especially the Strombidium(accounting for 41%of the total abundance).The microzooplankton abundance was significantly positively correlated with the concentration of Chl a.3.The results of dilution experiments were as follows:In the EIO during autumn in 2016,the phytoplankton growth rates(?0)ranged from 0.44-1.88 d-1(0.96±0.35 d-1);the microzooplankton grazing rates(m)ranged from 0.18-1.26 d-1(0.58±0.27 d-1);the ranges of microzooplankton grazing pressure on phytoplankton standing stock(Pi)and primary production(Pp)were 16.23%-71.63%(42.28±13.72%)and 31.70%-256.85%(77.29±42.62),respectively.There were also high growth and grazing rates at Sites S06 and S01-17.In the central and northern SCS during spring in 2017,the(?0)ranged from 0.45-1.52 d-1(0.85±0.28 d-1);the m ranged from 0.20-0.87 d-1(0.45±0.22 d-1);the ranges of Pi and Pp were 18.13%-58.05%(35.15±13.22%)and 36.74-91.15%(62.92±17.05%),respectively.Because there were obviously differences in environmental factors between the central and northern SCS,the ?0,m,Pi,and Pp in the central SCS were lager than those in the northern SCS.In the western SCS during autumn in 2017,the ?0 ranged from-0.3-1.65 d-1(0.71±0.43 d-1);the m ranged from 0.12-1.13 d-1(0.58±0.27 d-1);Pi and Pp were 11.31%-67.70%(42.21 ± 15.71%)and 26.49-126.53%(79.09±24.54%),respectively.4.The microzooplankton grazing rate was significantly correlated with the abundance of microzooplankton.The temperature and Chl a concentration were the main factors affecting the abundance of surface microzooplankton.The growth rates and grazing rates were highly coupled in different sea areas,that means,the larger growth rate of phytoplankton,the larger grazing rate of microzooplankton.