Community Composition And Seasonal Dynamic Of Planktonic Protist In Sanshan Island,Laizhou Bay

As a member of planktonic eukaryotic microorganisms,protist is one of the important ecological groups possessing incredibly high abundance and species diversity.Ciliates,the most specialized protozoa,can quickly adapt to the changing environment and play an essential role in the planktonic ecosystem.Protists in coastal waters are affected by both human activity and natural factors,thus showing certain community composition as well as spatial and temporal distributing patterns.However,the diversity of protists,community composition and seasonal dynamic in coastal water with intensive anthropic disturbance remains largely unknown,especially in Laizhou bay.In this study,traditional morphological methods combined with high-throughput sequencing technology(HTS)to investigate the diversity and community structure of planktonic protists and ciliates in the coastal waters of Yantai.In addition,seasonal changes in the planktonic protist community and the multiple environmental parameters are also provided in the present study,which provides beneficial references for the study of long-term variation of planktonic protists and their response mechanism to environmental factors in the semi-closed temperate bay.The following conclusions could be drawn:(1)HTS for the V4 region of the 18 S r RNA gene showed that Alveolata,Chlorophyta and Stramenopiles were the dominant protists.Among them,dinoflagellates were the dominant group in both species diversity and relative abundance.The community composition of planktonic protists appears obvious seasonal variation,and species diversity is highest in winter.Both alpha and beta diversity shows significant seasonal variation but no considerable difference in spatial distribution.Redundancy analysis demonstrated that total organic carbon and dissolved oxygen content were the environmental factors in shaping the significant season variation of the planktonic protist community in the coastal water of Sanshan Island.(2)Aloricate oligotrichs(40.14%)and tintinnids(10.67%)were the dominant groups in the planktonic ciliate community.The relative abundance of oligotrichs mainly consisted of Strombidium and Strombidiidae?X,and was highest in winter.The relative abundance of tintinnids was mainly composed of Tintinnida?XX,Tintinnopsis and Favella,and they were highest in spring and summer.Both the seasonal and spatial distribution of the planktonic ciliate community was no significant difference.Total organic carbon and dissolved oxygen content were the environmental driving factors in shaping the seasonal variation of the planktonic ciliates community.Compared to the offshore sampling site,the diversity and relative abundance of tintinnids at the quay site were lower,but the occurrence frequency of the tintinnids with arenaceous lorica is higher.Probably the frequent wave shocks and artificial disturbances that affect the spatial distribution pattern of the dominant species.A total of 17 species were identified by means of microscopic observation and 18 S single-cell sequencing,belonging to seven genera(Tintinnopsis,Codonellopsis,Favella,Eutintinnus,Frontonia,Didinium,Spirostrombidium).The diversity and frequency of tintinnids were the highest.(3)The possibility of habitat extension of ciliates is exist when the confluence happens between marine and freshwater,and marine ciliates collected in this research study were also found in freshwater.The morphological and ontogenetic research of a freshwater hypotrich ciliate which could tolerate low salinity was carried out.A new genus(Monopleurotricha nov.gen.)was established to correct misidentification and misattribution.Phylogenetic analysis of SSU r RNA also confirmed the establishment of the new genus.