Marine Bacterial Communities in the Xisha Islands, South China Sea

Abstract

Oligotrophic marine environments are ecological funnels in marine ecosystems and are essential for maintaining the health and balance of the entire marine ecosystem. Bacterial communities are one of the most important biological populations, which can survive in low-nutrient environments and perform a variety of important ecological functions, such as decomposing and absorbing organic waste in the ocean and converting nitrogen from the atmosphere into a usable nitrogen source, thus maintaining the health of marine ecosystems. The bacterioplankton community composition and potential function were analyzed using 16S rRNA gene amplicon sequencing in oligotrophic coral reef sea areas. The diversity of the bacterial community exhibited significant differences between the four studied regions. Proteobacteria (38.58–62.79%) were the most abundant in all sampling sites, followed by Cyanobacteria (15.41–37.28%), Bacteroidota (2.39–6.67%), and Actinobacteriota (0.45–1.83%). Although bacterioplankton communities presented no difference between surface and bottom water regarding community richness and α-diversity, the bacterial community composition presented significant differences between surface and bottom water regarding β-diversity. Alteromonadales, Rhodospirllales, and Chloroplast were identified as the significantly different communities between the surface and bottom (Q value < 0.01). Bacterial community distribution in different regions was mainly affected by pH, dissolved oxygen, and nutrients. Nitrite ammonification, chitinolysis, predatory or exoparasitic, chloroplasts, chemoheterotrophy, aerobic chemoheterotrophy, phototrophic, compound degradation (mostly nutrients and pollutants), nitrogen cycle, fermentation, and intracellular parasitism were the dominant functions in the four regions.