Spatiotemporal Patterns in Diversity and Assembly Process of Marine Protist Communities of the Changjiang (Yangtze River) Plume and Its Adjacent Waters

Abstract

Marine protists are highly heterogeneous and play key roles in the structure and functioning of marine ecosystems. However, little is known on the underlying biogeographic processes and seasonal diversity patterns that shape their community assembly in a regional scale in marginal sea. In this study, we conducted high-throughput sequencing of 18S rRNA gene to survey the protist community compositions (PCCs) of the Changjiang (Yangtze River) plume, an intensely human-affected coastal area, to the adjacent continental shelf waters over three seasons. Furthermore, the different impacts of environmental and spatial factors on marine PCCs were examined. The results revealed significant dissimilarities of PCC’s diversity among seasons and habitats, with more obvious seasonal variations in the Changjiang plume. Procrustes analysis showed better consistency of the community-environment relationship in shelf area, further supported by stronger correlation coefficients computed in the Mantel tests. This might be explained by seasonal dynamics of Changjiang Diluted Waters (i.e., the mixing of the Changjiang runoff with inshore water of the East China Sea) that changed the environmental conditions of coastal area dramatically, resulting in lower importance of spatial factors (dispersal limitation) on PCCs compared with environmental filters, including physicochemical properties (e.g., water temperature, salinity, dissolved oxygen, and nutrients), as well as biotic factors (e.g., Chl a and food abundance). This was further explained by higher immigration rate and fitness to neutral model, which suggested a predominant role of neutral process in shaping the PCCs in coastal area. Different richness, diversity, and taxonomic compositions but comparable biogeographic patterns were observed among abundant and rare sub-communities. In general, the abundant sub-communities exhibited higher dispersal ability which tend to respond to environmental selection during dispersal, whereas the rare sub-communities appeared to be present only in few samples due to dispersal limitation. Co-occurrence network further indicated the importance of biotic interactions in community assembly and potential roles of rare taxa in maintaining the community structure. Overall, this study suggests the dynamic in the biogeographic patterns of PCCs of the Changjiang plume to the adjacent waters in the ECS responding with the changing environmental conditions and geographical factors.

Micromonas, a small pigmented flagellate, predominates the nanoflagellate and photosynthetic picoeukaryote communities in the northern South China Sea

“…Thus, Micromonas has the potential to be the dominant contributor to PPE and PNF communities in the ocean (Sherr et al, 2003 ). Previously, the approach of HTS was mainly used to explore the biodiversity, community composition and biogeographic distribution of natural assemblages of microbial eukaryotes in many studies, where the relative abundance of Micromonas and its biogeography was also realized (Guo et al, 2020 ; Marquardt et al, 2016 ; Massana et al, 2015 ). However, the relative abundance of Micromonas and its role in the microbial community could be rather underestimated with the HTS approach, because its genomic information could be covered by the high number of rRNA gene copies of the larger protists with larger genomes (Keeling & del Campo, 2017 ).…”

Bacterial and Protistan Community Variation across the Changjiang Estuary to the Ocean with Multiple Environmental Gradients

“…Global surveys of bacterial diversity have demonstrated that salinity is the major environmental determinant of bacterial community composition [ 4 ]. Besides nutrients, other environmental factors such as temperature, dissolved oxygen and pH are known to determine microbial community structure in estuarine and marine environments [ 5 , 6 , 7 , 8 , 9 ].…”

“…Moreover, the Changjiang Estuary and its adjacent areas are influenced by multiple water masses from different directions [ 34 ]. Previous studies revealed that salinity, temperature, nutrients, dissolved oxygen and other environmental factors regulate the planktonic microbial community composition in the Changjiang Estuary and its adjacent waters [ 5 , 35 ]. However, the primary determinant of microbial community composition in this complex environment has not been clarified.…”