[Effects of Coastal Organic Pollution on Bacterioplankton Community in Sanmen Bay]

Coastal organic pollution has become a serious problem, thus it is imperative to assess the potential effects on the marine environment. The microbes are generally the first responders to environmental perturbation, which may serve as biological indicators for pollution levels. In this study, we collected surface seawater samples from Sanmen Bay and adjacent Yushan Reserve. Using an Illumina sequencing based analysis of bacterial 16S rRNA gene, we explored the effect of organic pollution on the bacterioplankton community compositions (BCCs). The results showed that the organic pollution (A) was 4.57±2.41 at Sanmen Bay, which was significantly higher (P<0.001) than that in Yushan Reserve (0.43±0.74). The bacterial diversity and community compositions differed significantly between the two locations. Specifically, the relative abundance of Actinobacteria, α-Proteobacteria, β-Proteobacteria, SAR406 in Sanmen Bay was significantly higher than that in Yushan Reserve, while Bacteroidetes, Cyanobacteria, Planctomycetes exhibited an opposite change pattern. A multivariate regression tree analysis showed that the bacterial diversity was primarily affected by water pH, organic pollution and chlorophyll a levels, which respectively explained 27.7%, 15.6% and 6.7% variance in bacterial diversity. A redundancy analysis (RDA) revealed that the bacterioplankton community was significantly controlled by pH, salinity and organic pollution, which cumulatively explained 14.8% of the variation in BCCs. In addition, the geographic distance was significantly (P <0.001) correlated with BCCs, accounting for 4.42% variance, which suggested that the spatial distribution of bacterioplankton community was non-random. Moreover, this study screened 23 sensitive bacterial families, whose relative abundances were significantly associated the organic pollution. For a given bacterial family, the change pattern of relative abundance was consistent with its known function, thus holding the potential for indicating organic pollution levels. To conclude, this study showed that the increasing coastal organic pollution had altered BCCs, and enriched the relative abundances of potential pathogens. Furthermore, the sensitive bio-indicators were screened for evaluating the increasing organic pollution level.