| The mass occurrence of giant jellyfish Nemopilema nomurai has become a common phenomenon in the Yellow Sea and East China Sea in recent years. Nanoplankton（mainly phototrophic and heterotrophic nanoflagellates） and microplankton（mainly dinoflagellates and ciliates） has long been considered as important mediators of matter circulation and energy flow from the microbial loop to classic food web. However, relationship between nano- and micro-zooplankkton in particular ciliate and the giant jellyfish remains unclear. Abundance, biomass, productivity and the community structure of nano- and microzooplankton（flagellates, ciliates, copepod nauplii, Noctiluca scintillans） in surface and 10 m layer water in the Yellow Sea and East China Sea were investigated through sampling and observing under microscope during the jellyfish decaying in October 2012 and the jellyfish fast growth and spreading in June, blooming in August and September 2013 and their relationships with jellyfish bloom and environment factors were discussed.Nanoflagellates Total abundance and biomass of flagellates in the surface water among the four investigations show Octuber 2012(718±314 ind·m L-1, 40.54±15.14 mg·C·L-1) > June 2013(381±234 ind·m L-1, 8.49±7.89 mg·C·L-1) > August 2013(222±164 ind·m L-1, 6.80±6.31 mg·C·L-1) > September 2013(160±102 ind·m L-1, 5.27±6.39) mg·C·L-1, same result was showed in the 10 m water. Both abundance and biomass of PNF（prototrophic nano-flagellates） in surface water in June 2013 and in surface and 10 m water in September 2013 had negative correlation with tempreture as well as salinity.Ciliates A total of 72 species belonging to 38 genera were sorted. The abundance and biomass of ciliates were respectively(3184±2620 ind·L-1, 6.78±4.07 mg·C·L-1), in the surface water and(2490±2064 ind·L-1, 7.08±6.09 mg·C·L-1) in the 10 m water in October 2012, changed to(2439±2679 ind·L-1, 12.79±16.89 mg·C·L-1) in surface water and(1516±1126 ind·L-1, 10.76±14.47 mg·C·L-1) in the 10 m water in June 2013, sharply decreased to(1193±1318 ind·L-1, 4.78±5.23 mg·C·L-1) in surface water and(898±904 ind·L-1, 3.55±3.53 mg·C·L-1) in 10 m water in August 2013 and boost up to(3088±4623 ind·L-1, 9.52±9.97 mg·C·L-1) in the surface water and(2098±2339 ind·L-1, 5.20±4.88 mg·C·L-1) ind·L-1 in 10 m water in September 2013。The productivity of ciliates were respectively 10.48±6.83 μg C·L-1·d-1 in surface water and 9.38±6.84 μg C·L-1·d-1 in the 10 m water in October 2012, incresead to 16.07±17.26 μg C·L-1·d-1 in surface water and 13.34±15.36 μg C·L-1·d-1 in the 10 m water in June 2013, quickly droped to 9.86±10.18 μg C·L-1·d-1 in surface water and 12.49±12.76 μg C·L-1·d-1 in the 10 m water in August 2013, slightly decreased to 9.82±10.53 μg C·L-1·d-1 in surface water and 10.27±9.74 μg C·L-1·d-1 in the 10 m water in September 2013. Four investigation shows that ciliates in the surface and 10 m water had much greater abundance, biomass and productivity in the adjacent sea area of Changjiang estuary and the nearshore stations at the transects of C（36°N） and E（35°N）, and had less abundance, biomass and productivity in the nearshore stations at the transect of G（34°N）. Cluster analysis based on ciliate species-abundance in June, August and Seotember 2013 shows that there was a steady difference in community structure between transects in the Norhern Yellow Sea and transects in the Southern Yellow Sea and the East China Sea which is deeply influenced by the Changjiang Runoff. Cluster analysis based on ciliate species-abundance at transects E, G and I in June, August and September 2013 shows that there is a clear difference in community structure between the initial stage of jellyfish bloom（June 2013） and the increase and the mass occurance of jellyfish（August and September 2013）. Abundance, biomass and productivity of ciliates have no steady correlation with tempreture, salinity as well as abundance and biomass of PNF and HNF. We assume that the nutrients relased by dead jellyfish and predation of mesozooplankton eventually contribute to the hugely increase of the abundance of Mesodinium rubrum in September 2013.Noctiluca scintillans & Copepod nauplii Copepod nauplii were found only in June and August 2013. Both the biomass(0.13±0.18, 0.10±0.14 mg·C·L-1) and productivity(0.03±0.04, 0.03±0.05 μg C·L-1·d-1) were far less than those of ciliates. The abundance of Noctiluca scintillans in June 2013 was much more than that in August and September 2013 which may be caused by the temperature difference.The study shows that the biomass and productivity of ciliates are much more than that of copepod nauplii during the mass occurrence of giant jellyfish in 2013. Compared with copepod nauplii, ciliates have quantitative advantage which makes it easier for giant jellyfish to prey and its high productivity serve food during mass occurrence of giant jellyfish. Based on the dynamics of the ciliate community structure and production before and during the mass occurrence of Nemopilema nomurai, we conclude that ciliates might provide important food supply for the giant jellyfish, and were affected by the giant jellyfish directly and indirectly（cascading） effect. |
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