Study On The Planktonic Ciliates Diversity In Taiwan Strait

Marine planktonic ciliate is a large assemblage of single-celled protozoan,characterized by minute body size and high diversity,and is an important component of micro-plankton community.In marine ecosystem,planktonic ciliate can act as a link between the microbial loop and classical food web by grazing the heterotrophic bacteria and thus enhance the transfer efficiency of energy and organic matter.Several studies had been carried out to investigate relationship between microorganism and water mass,such as bacteria,fungi,and microphytoplankton,etc.However,there are few such studies focusing on the ecological distribution of ciliates drived by water masses.In addition,studies of temporal variations of ciliate community were mainly on seasonal/interannual scales,whereas that on short time scale,such as hours to days,was largely unknown.To bridge the gaps,we analyzed ciliate distribution pattern using high throughput sequencing in Taiwan Strait which was characterized by possessing multiple water masses for whole year.In addition,we conducted observations of high frequency temporal variation(4-6 hours per sampling and up to 72 hours)of ciliate community at two time-series stations which located in the continental shelf and the continental slope in the strait.Our results as follows:(1)Ciliate community consisted of 11 classes,named of Spirotrichea,Phyllopharyngea,Oligohymenophorea,Colpodea,Litostomatea,Prostomatea,Heterotrichea,Ciliophora-5,Ciliophora-6,Ciliophora-7 and Ciliophora-10.Among them,the Spirotrichea ciliate was the most dominant group,which was followed by the Phyllopharyngea,accounting for 18.49%;the proportions of Oligohymenophorea and Colpodea were lower,with 9.91%and 7.93%,respectively;the proportions of Heterotrichea,etc.were relatively small,all less than 1%.(2)The alpha diversity varied in water masses,with high diversity occurring in plume water and open sea region and low diversity occurring in upwelling area.Typically,alpha diversity was higher nearshore than offshore in the strait.Correlation analysis indicated that diversity of ciliate was not correlated with all environmental factors.(3)We found that a significant influence of water masses on the distribution pattern of ciliates,which was believed to reduce proportionally the variation explained by environmental parameters at the scale of the total water masses,indicating that the effect of water mass movement on the ciliate community was stronger than the environmental factors.Environmental variables had a high degree of explanation for community changes within different water masses,and environmental variables regulating ciliate community structure were different in different water masses.(4)There were significant differences in the alpha diversity and community composition of ciliates between C6 and C9 stations.The alpha diversity of C9 station was higher than that of C6 station.The ciliate communitis at both stations consisted of Spirotrichea,Phyllopharyngea,Colpodea,Oligomynophorea,Litostomatea,Prostomatea,Heterotrichea,Ciliophora-5,Ciliophora-7,Ciliophora-10 and Ciliophora-X.In C6 station,Spirotrichea was the most dominant group,with a proportion of 55.07%,followed by the Phyllopharyngea,which accounted for 26.57%.Besides Spirotrichea,the top four assemblages of ciliate community were Colpodea,Oligomynophorea and Litostomatea,possessing proportion of 11.89%,3.57%and 2.17%,respectively.Compared to that of C6,the proportion of Spirotrichea at C9 station decreased to 40.19%,whereas Phyllopharyngea,Colpodea,and Oligohymenophorea all increased by 14.03%compared with that of C6 station.(5)At C6 station,ciliate community grouped into two clusters,3 ?m and 20 ?m,indicating that size fraction was the main influence factor of ciliate community on continental shelf area.Ciliate community had a obvious vertical distribution pattern at C9 station,and it was controlled by food,i.e.nanoflagellata and bacteria.In addition,there was a significant difference in community structure of ciliates between photic(less than 100 m)and twilight zones(ANOSIM,R=0.239,p=0.009).(6)Sequencing on both rRNA and rDNA of nano sized ciliates showed that rDNA and rRNA based communities were significant different,therefore clearly separated from each other in ordination plot.Spirotrichea was absolutely dominant in rDNA dataset,however,was greatly reduced in rRNA samples,which might be due to its high rDNA copy number.Further statistical analysis showed that there was significant difference in community compostions between rRNA and rDNA datasets(ANOSIM,R=0.6852,p=0.001).The ratio of rRNA:rDNA was used to represent the metabolic activity of ciliates and analysis showed that there were no significant differences in the activity of ciliates among different water depths,times and stations,indicating their activity had no significant changes on the continental shelf and slope on short time scale.