Seasonal Dynamics of Planktonic Protist Diversity and Community Assembly in the Northern East China Sea

This study investigated planktonic protists in the northern East China Sea (NECS) to evaluate their diversity, community assembly processes, and primary production across seasons. Sampling took place during three cruises in May, July, and October 2023. Using small organelle-enriched metagenomics, we identified 537 operational taxonomic units (OTUs) throughout the NECS. While regional differences were negligible, significant seasonal changes emerged, with higher phylogenetic clustering in summer—indicating strong environmental influences on community assembly. Metagenomic analysis revealed diverse protist taxa across surface (SUR), deep chlorophyll maximum (DCM), and bottom (BOT) layers. Microbial eukaryotes—including Bacillariophyta, Cryptophyta, Dinoflagellates, and Ochrophyta—displayed significant variability in community composition across depths. Bacillariophyta and Ochrophyta dominated the DCM and BOT layers, suggesting that nutrients and light influence microbial communities. Analysis of trophic modes unveiled vertical stratification with six modes identified. Obligate Photoautotrophs (OPA) and Constitutive Mixotrophs (CM) dominated all depths, highlighting the importance of mixotrophy. The SUR layer exhibited greater diversity, including opportunistic and competitive modes, while the DCM and BOT layers were characterized by neutral and heterotrophic modes. Heterotrophs (HET) increased in the DCM and SUR layers. General and Engulfing Specialist Non-Constitutive Mixotrophs (GNCM, eSNCM) were less common; Parasitic Specialist Non-Constitutive Mixotrophs (psSNCM) were rare. Non-metric multidimensional scaling (NMDS) analysis revealed significant seasonal but no depth-related differences, emphasizing that temperature and nutrients primarily drive protist dynamics in the NECS. Community assembly analysis indicated that 85.2% of the communities were undominated by specific ecological processes, with environmental selection and dispersal mechanisms playing minor roles. These findings highlight mixotrophy as a key adaptive strategy in the variable marine environment of the NECS.

Presentation Preference: Oral

Primary Presenter: Kwang Young Kim, Department of Oceanography (kykim@chonnam.ac.kr)

Authors:

Kwang Young Kim, Chonnam Naitonal University  (kykim@chonnam.ac.kr)

Juhee Min, Chonnam National University  (minzooey@gmail.com)