Diversity, Composition, and Activities of Nano- and Pico-Eukaryotes in the Northern South China Sea With Influences of Kuroshio Intrusion

Abstract

Nano- and pico-eukaryotes play important roles in the diversity and functions of marine ecosystems. Warm, saline, and nutrient-depleted water that originates in the Kuroshio Current seasonally intrudes into the northern South China Sea (NSCS) from autumn to spring. To clarify the mechanisms in shaping the community structure of nano- and pico-eukaryotes as well as impacts of the Kuroshio intrusion on the NSCS ecosystem, genomic DNA and RNA were co-extracted from samples collected at two depths from nine stations, and then the V9 region of 18S rDNA and rRNA was sequenced with high-throughput sequencing. Our results showed that Dinophyceae was the most diverse and abundant nanoeukaryotic group during the study period revealed by both DNA and RNA surveys. In contrast, the relative read abundance of MAST, Pelagophyceae, and Dinophyceae in the size fraction of picoeukaryotes might be largely underestimated by the DNA survey. The RNA survey was the more reliable method to investigate the eukaryotic community structure. Environmental filtering played an important role in shaping the community structure, and the sampling depth became the governing factor of the beta diversity under the environmental setting of stratification during the study period. The spatial variations in the diversity of nanoeukaryotes were subject to the dispersal limitation under the size rule. The effects of the Kuroshio intrusion on the nanoeukaryotic community structure might also be explained by the dispersal limitation. Overall, neutral processes are critical in shaping the community structure of nanoeukaryotes. The relative metabolic activities of nanoeukaryotes were relatively stable in accordance with the high similarity of community structure between sampling sites. The responses of the relative metabolic activities of picoeukaryotes to environmental factors displayed two distinct patterns: positive correlations with salinity and nutrients and negative with temperature for Dinophyceae, MAST, and Pelagophyceae, while reversed patterns for Mamiellophyceae and Radiolaria. Our findings improve the understanding of the nano- and pico-eukaryotic communities in the NSCS and the mechanisms of their assembly.

Phytoplankton Diversity and Co-Dependency in a Stratified Oligotrophic Ecosystem in the South Adriatic Sea

“…Interestingly, there were no E. huxley ASVs in our dataset, nor was it recorded via light microscopy, which can be corroborated with the findings of Piredda et al, 2017 [70] and Gran-Stadniczeñko et al, 2019 [95]. They noted that higher abundances of Emiliania huxley regarding the V4 region of the 18S rRNA gene are expected in late summer and fall in coastal seas [98,100], allowing us to conclude that the period of our experiment was not favorable for E. huxley growth.…”

“…The bias of comparing taxa lists obtained by different observers/taxonomers should be considered, as well as seasonality, sampling location, and the different methodologies used, as shown in the more diverse dinoflagellate community revealed by HTS vs. microscopy. Some genera were recorded only via the 18S rRNA ASVs: Ceratoperidinium, Karlodinium, Azadinium, Lepidodinium, Blastodinium, Heterocapsa, Karenia, Torodinium, Biecheleria, Pelagodinium etc., all of which were reported previously in the South Adriatic [71] and in other coastal marine areas [73,[96][97][98]. Relative abundances of ASVs belonging to dinoflagellate genera revealed their dominance in the phytoplankton community, especially Gyrodinium, which was dominant in reads in all samples, with the highest number observed in the surface pico-fraction collected at the beginning of experiment (13 July 2021) (Supplementary Figure S1).…”

Diversity and assembly processes of microbial eukaryotic communities in Fildes Peninsula Lakes (West Antarctica)

“…The analysis of the OTUs obtained using the UP-ARSE clustering method have been widely used for highthroughput sequencing analysis (Gad et al, 2022;Xu et al, 2022;Zhang et al, 2022;Reboul et al, 2021;Sun et al, 2022). Some of the diversity indices in our study were more comparable to previous research using 97 % sequence similarity OTUs (Chen et al, 2022;Wang et al, 2021;Y. Wang et al, 2020), as comparisons of these statistics using the same bioinformatics tool seem to remain persuasive Glassman and Martiny, 2018).…”

“…Compared to other aquatic ecosystems (Wang et al, 2021;Y. Wang et al, 2020;Hernandez-Ruiz et al, 2018), the diversity of microbial eukaryotes in the Antarctic lakes studied here was significantly lower (Shannon index 1.…”

Cell size is a key ecological trait associated with biogeographic patterns of microbial eukaryotes in coastal waters

“…This likely explains the big changes in biogeographic patterns of microbial eukaryotes that occur in the coastal waters. The data we acquired in this new estuarine region survey, when combined with those from previous studies conducted in the upper Pearl River Delta (Zou et al, 2021), Pearl River-South China Sea Continuum (Wu and Liu, 2018), and offshore South China Sea (Wang et al, 2021), will together provide a more complete picture of the microbial eukaryotic communities in this region. Moreover, size-fractionated microbial eukaryotes have previously been investigated in some isolated coastal locations (Massana et al, 2015;Genitsaris et al, 2016;Elferink et al, 2020); however, they have not been well documented via a fine sampling design over an entire estuary.…”