Eukaryotic Plankton Community Assembly and Influencing Factors between Continental Shelf and Slope Sites in the Northern South China Sea

Abstract

Eukaryotic plankton are pivotal members of marine ecosystems playing crucial roles in food webs and biogeochemical cycles. However, understanding the patterns and drivers of their community assembly remains a grand challenge. A study was conducted in the northern South China Sea to address this issue. Here, 49 samples were collected and size-fractionated from discrete depths at continental shelf and continental slope in the northern South China Sea over a diel cycle. From high throughput sequencing of the 18S rDNA gene V4 region, 2,463 operational taxonomic units (OTUs) were retrieved. Alveolata and Opisthokonta overwhelmingly dominated the assemblages in the abundance (44.76%, 31.08%) and species richness (59%, 12%). Biodiversity was higher in the slope than the shelf and increased with depth. Temperature and salinity were found as the major deterministic drivers of taxon composition. Community structure was influenced by multiple factors in the importance order of: environmental factors (temperature + salinity) > spatial factor > water depth > sampling time. Furthermore, the neutral model explained more variations in the smaller-sized (0.22-3 µm) community (24%) than larger-sized (3-200 µm) community (16%) but generally explained less variations than did deterministic processes. Additionally, our data indicated that the larger plankton might be more environmentally filtered and less plastic whereas the smaller plankton had stronger dispersal ability. This study provides novel insights into differential contributions of the deterministic process and stochastic process and complexities of assembly mechanisms in shaping the community assembly of micro-nano and pico-eukaryotic biospheres in a subtropical ocean.

Keywords: Eukaryotic plankton, South China Sea, deterministic, stochastic, disperse, process