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Numerous studies have shown that changes in environmental factors can significantly impact and shift the structure of phytoplankton communities in marine ecosystems. However, little is known about the association between the ecological stoichiometry of seawater nutrients and phytoplankton community diversity and stability in subtropical bays. Therefore, we investigated the relationship between the phytoplankton community assemblage and seasonal variation in the Beibu Gulf, South China Sea. In this study, we found that the abundance of Bacillariophyceae in spring was relatively greater than in other seasons, whereas the abundance of Coscinodiscophyceae was relatively low in spring and winter but greatly increased in summer and autumn. Values of the alpha diversity indices gradually increased from spring to winter, revealing that seasonal variations shifted the phytoplankton community structure. The regression lines between the average variation degree and the Shannon index and Bray–Curtis dissimilarity values showed significantly positive correlations, indicating that high diversity was beneficial to maintaining community stability. In addition, the ecological stoichiometry of nutrients exhibited significantly positive associations with Shannon index and Bray–Curtis dissimilarity, demonstrating that ecological stoichiometry can significantly influence the alpha and beta diversity of phytoplankton communities. The C:N:P ratio was not statistically significantly correlated with average variation degree, suggesting that ecological stoichiometry rarely impacted the community stability. Temperature, nitrate, dissolved inorganic phosphorous, and total dissolved phosphorus were the main drivers of the phytoplankton community assemblage. The results of this study provide new perspectives about what influences phytoplankton community structure and the association between ecological stoichiometry, community diversity, and stability in response to environmental changes. [ABSTRACT FROM AUTHOR]

Vibrio are widely distributed in aquatic environments and strongly associated with eutrophic environments and human health through the consumption of contaminated seafood. However, the response of the Vibrio community to seasonal variation in eutrophic environments is poorly understood. In this study, we used a Vibrio -specific 16S rRNA sequencing approach to reveal the seasonal distribution pattern and diversity of the Vibrio community in the Maowei Sea, Beibu Gulf of China. The Shannon diversity of the Vibrio community was highest in the summer, while β-diversity analysis showed that Vibrio community structures were significantly different between seasons. Distance-based redundancy analysis (dbRDA) and Mantel test analysis suggested that total dissolved nitrogen (TDN), total dissolved phosphorus (TDP), dissolved inorganic nitrogen (DIN), salinity, and temperature were the key environmental factors shaping the Vibrio community structure, indicating a strong filtering effect of trophic condition on Vibrio communities. Furthermore, through random forest analysis, V. fluvialis , V. alginolyticus , V. proteolyticus , V. splendidus , and the other eight Vibrio species were more sensitive to eutrophic changes. This study revealed seasonal changes in Vibrio communities and the influence of environmental variation on Vibrio community composition, contributing to a better understanding of their potential ecological roles in a subtropical inland bay. [ABSTRACT FROM AUTHOR]

Phaeocystis globosa blooms are recognized as playing an essential role in shaping the structure of the marine community and its functions in marine ecosystems. In this study, we observed variation in the alpha diversity and composition of marine free-living bacteria during P. globosa blooms and identified key microbial community assembly patterns during the blooms. The results showed that the Shannon index was higher before the blooming of P. globosa in the subtropical bay. Marinobacterium (γ-proteobacteria), Erythrobacter (α-proteobacteria), and Persicobacter (Cytophagales) were defined as the most important genera, and they were more correlated with environmental factors at the terminal stage of P. globosa blooms. Furthermore, different community assembly processes were observed. Both the mean nearest relatedness index (NRI) and nearest taxon index (NTI) revealed the dominance of deterministic factors in the non-blooming and blooming periods of P. globosa , while the bacterial communities in marine waters after the blooms tended to be controlled by stochastic factors. Our findings revealed that the assembly of the bacterial community in marine P. globosa blooms is a complex process with mixture effects of marine microbiomes and environmental parameters. [ABSTRACT FROM AUTHOR]

In this study, we investigated the specific bacterial distribution and the response of bacterial communities to shifts in environmental factors in the subtropical Beibu Gulf, southern China. The abundances of Actinobacteria, Bacilli, Planctomycetia, Thermoleophilia, Anaerolineae, and Synechococcophycideae were significantly higher in high eutrophic samples than in medium eutrophic and oligotrophic samples. Bacterial alpha-diversity was found greater in high eutrophication samples than in the other samples. Besides, Ponticaulis koreensis , Nautella italic , Anaerospora hongkongensis , Candidatus Aquiluna rubra , and Roseovarius pacificus were sensitive to trophic variation and thus could be used as eco-markers. In addition, the relative abundances of functional genes involving carbohydrate and amino acid metabolism were very high among the samples. We also found temperature, Chl- a , TDN and NO 3 − were the main environmental drivers of bacterial community structure. Overall, this study provides new insight into the composition of bacterial community and function response to gradients of eutrophication in Beibu Gulf. • The greatest bacterial α-diversity was observed in high eutrophication samples. • Specific bacteria could be used as eco-markers in Beibu Gulf. • Carbohydrate and amino acid metabolism related genes were dominant in the samples. • Temperature, Chl- a , TDN and NO 3 − were the main drivers of bacterial composition. [ABSTRACT FROM AUTHOR]