Monthly Variation, Environmental Drivers, and Ecological Functions of Marine Bacterial Community in a Eutrophic Coastal Area of China

Abstract

This study investigated the monthly variations of bacterial communities in the surface seawater of the Wenzhou coastal area and their influencing factors, while exploring the ecological functions of microbial communities. The results indicated that the surface seawater bacterial communities in this region exhibited high diversity, with significantly higher diversity observed in the winter half-year compared to the summer half-year. The bacterial community structures showed distinct monthly variations, with high similarity between adjacent months, particularly from June to September. The dominant bacterial taxa primarily included Proteobacteria represented by the SAR86 clade, OM43 clade, and Rhodobacteraceae; Bacteroidota represented by Flavobacteriaceae; and Cyanobacteria mainly composed of Cyanobium PCC-6307 and Synechococcus CC9902. Temperature and nitrate ions were identified as the environmental factors most strongly correlated with monthly bacterial community variations, while dissolved oxygen, nitrite ions, and total organic carbon also showed significant correlations with relative abundances of certain taxa. Predictions of the bacterial community's ecological functions revealed that chemoheterotrophic functions were most abundant throughout the year, whereas photoautotrophic functions were primarily enriched in summer. Denitrification and other nitrogen cycling-related functions also displayed obvious monthly variations. Collectively, this study provides valuable insights into the temporal changes in coastal microbial communities and their interactions with different environments.

Keywords: bacterial communities; ecological functions; environmental factors; monthly variations; surface seawater.

Figure 1

The red dots indicate the sampling locations. Water samples were collected monthly at a fixed sampling point, with consistent sampling conducted at a depth of 1 m below the water surface.

Figure 2

Beta diversity of marine microbial communities: (a) cluster analysis at the OTU level; (b) PCA analysis at the OTU level. The inter-group R² value was 0.3967 (p = 0.019, p < 0.05). Principal component 1 (PC1) explained 20.85% of the variance, while principal component 2 (PC2) accounted for 16.74% of the variance (PoV: Proportion of Variance). The samples are designated as SW_4 (corresponding to April), SW_5 (May), and so forth up to SW_12 (December); SW_1, SW_2, and SW_3b represent samples from the following year’s January, February, and March, respectively. The same convention applies to the figure below.

Figure 3

Microbial Community Composition: (a) Phylum; (b) Family; (c) Genus.

Figure 4

Venn diagrams of microbial community composition at the Phylum, Family, and Genus levels: (a) analyze by month; (b) analyze by season.

Figure 5

RDA analysis of environmental factors and marine microbial communities: (a) Phylum; (b) Family; (c) Genus.

Figure 5

RDA analysis of environmental factors and marine microbial communities: (a) Phylum; (b) Family; (c) Genus.

Figure 6

Heatmap of correlation analysis between species and environmental factors at the Family level (* 0.01 < p ≤ 0.05, ** 0.001 < p ≤ 0.01, *** p ≤ 0.001).

Figure 7

Heatmap of the relative abundance of ecological functions.

Figure 8

Bar plot of intergroup functional differences (* 0.01 < p ≤ 0.05): (a) Significant Differences in Ecological Functions Among Different Seasonal Groups; (b) Significant Differences in Ecological Functions Between Winter and Summer Half-Year Groups.

Figure 8

Bar plot of intergroup functional differences (* 0.01 < p ≤ 0.05): (a) Significant Differences in Ecological Functions Among Different Seasonal Groups; (b) Significant Differences in Ecological Functions Between Winter and Summer Half-Year Groups.