Community Structure And Construction Mechanism Of Ciliates Of The Front And Water Masses On Either Side Of The Front In The Taiwan Strait And The Northern South China Sea

Ciliates belong to the protozoan,Alveolates supergroup and phylum Ciliophora,which have various morphology and wide distribution.In marine planktonic ecosystem,ciliates can feed on pico-and nanoplankton,and can also be fed by zooplankton and fish larvae,thus linking the microbial food loop to the classical food chain,play a pivotal role in the material circulation and energy flow of marine ecosystem and have important ecological research significance.At present,studies on the response of planktonic ciliate communities to marine physical processes are very limited.Previous studies have mostly focused on changes in abundance and biomass of planktonic ciliates,with little detailed studies on changes in community composition and even less on the construction mechanism driving community changes.The Taiwan Strait and the northern South China Sea affected by the East Asian monsoon,the water mass movement has obvious seasonal variation.Different water masses meet and mix to form different horizontal or vertical high-gradient transition zones,namely fronts.Therefore,it is an ideal experimental site for studying the response of the ciliate community to the front.Based on this,this work will take the Taiwan Strait and the northern South China Sea as the study areas,and use high-throughput sequencing technology to explore the response of ciliate communities to the Zhe-Min coastal current-South China Sea warm current front,the Pearl River plume-East Guangdong upwelling front and water masses on either side of the front under the influence of northeast monsoon and southwest monsoon,respectively.The results are as follows:(1)Different from the previous results,the α diversity of the ciliates in the frontal zone was similar to that in the water masses on both sides of the frontal zone,and did not show a significant high value.In spring,the a diversity index of the frontal water(FW)was similar to that of the South China Sea warm current(SCSWC),and higher than that of the Zhe-Min Coastal Current(ZMCC).The main environmental factors affecting the diversity of ciliates in spring were seawater density and NH4+.In summer,the a diversity of upwelling water(UW)and deep water(DW)is higher in the northern South China Sea,and that of plume water(PW)is similar to that of frontal water(FW).The main environmental factor affecting the diversity of ciliates in summer is water depth.(2)The composition of the ciliate community in the water masses on both sides of the frontal zone was significantly different from that in the frontal zone.In spring,the total community composition of ciliates in different water masses in the Taiwan Strait was dominated by Spirotrichea,Litostomatea and Phyllopharyngea.In the Zhe-Min coastal current,Litostomatea is the characteristic group and the most dominant group.In both the front water and the South China Sea warm current,Spirotrichea is the characteristic group,and its contribution to the front water is relatively high.In summer,the total community composition of ciliates in different water masses in the northern South China Sea was dominated by Spirotrichea,Oligohymenophorea and Colpodea.In plume water and frontal water,Spirotrichea is the characteristic group.There were fewer characteristic species in the upwelling water,belonging to the class Phyllopharyngea and Oligohymenophorea.In the deep water,Oligohymenophorea is the characteristic group,and the proportion of Prostomatea is higher than that of other water masses.(3)The ciliate communities of the front and the water masses on both sides of the front were dominated by random processes,i.e.,dispersal limitation was the largest.The community structure was significantly related to spatial distance(geographical distance and water depth),water masses and environment,the influence of abiotic factors on the community was greater than that of biological factors.In spring,abiotic factors in the Taiwan Strait had a greater influence on the ciliate community in the water masses on the front and both sides of the Taiwan Strait,and the correlation was stronger than that of spatial factors.The contribution of temperature,salinity,dissolved oxygen and nitrate were the most significant,which could independently and significantly affect the community structure.The contribution of heterogeneous selection is higher than that of undominated process.In summer,the ciliate communities on the front and both sides of the front of the northern South China Sea were significantly affected by water depth.The influence of spatial factors was higher than that of abiotic factors,and the contribution proportion of undominated process increased,which was higher than that of heterogeneous selection.