Evaluation of the correlation of Sargassum fusiforme cultivation and biodiversity and network structure of marine bacteria in the coastal waters of Dongtou Island of China

Abstract

Sargassum fusiforme is widely cultivated in the temperate coastal areas, and is particularly abundant in China, Korea, and Japan. However, information about if large-scale seaweed cultivation can affect the bacterial community in the coastal sea area is limited. This study explores the effects of large-scale cultivation of Sargassum fusiforme on the biodiversity and network structure of marine bacteria in the coastal water of Dongtou Island, China. The diversity of marine bacteria in the surface waters was significantly higher than that in the bottom waters in the cultivation area and adjacent area. The α-diversity metrics showed no significant difference between surface waters and bottom waters in the open sea area. Additionally, permutational multivariate analysis of variances suggested a significant difference in the microbial community structure between location, which were sampled relative to the cultivation area. At the phylum level, the dominant phyla in all groups were Proteobacteria, Cyanobacteria, Actinobacteria and Bacteroidetes. Proteobacteria was the most abundant phylum, accounting for more than 65% in all groups. The redundancy analysis showed that environmental factors affected the bacterial communities, and the results of an aggregated boosted tree analysis indicated that dissolved oxygen was a critical factor in controlling the bacterial communities in the surface waters, NO3−-N and NH4+-N were identified as primary factors associated with the change in bacterial community composition in the bottom waters. Network analysis revealed that the negative interactions between species pairs were the major relationship in the microbial ecosystem. Bacterial communities at S. fusiforme location were associated with larger sub-modules and a larger number of keystone species. Alphaproteobacteria and Gammaproteobacteria were identified as the keystone species in all locations. The results of the present study suggested that the differences in biodiversity and network structure of marine bacteria might be associated with the S. fusiforme cultivation.