8. Elevated CO2 demonstrates insignificant impacts on bacterial community structure in a subtropical coastal mesocosm experiment

Xin Lin (1)*, Ruiping Huang (1), Yibin Huang (1), Kunshan Gao (1)

1 State Key Laboratory of Marine Environmental Science, Xiamen university, Xiamen, Fujian province, 361100, China
*Corresponding author: xinlinulm@xmu.edu.cn

Background
Set within an ecological framework, we investigated the effects of elevated CO2, contrasted with ambient CO2, on dynamics changes of bacterial communities during diatom bloom in a replicated subtropical seawater mesocosm experiment. The mesocosm experiment was conducted in FOANIC-XMU mesocosm platform located in the seawater of Wuyuan Bay, Xiamen, Fujian province, East China Sea (N24°31′48″, E118°10′47″) during the months of December 2014 and January 2015.

Methods
The pCO2 in the mesocosms was controlled by bubbling with air of high (HC, 1000 μatm) or low (LC, 395 μatm) pCO2. 16S rRNA V3-V4 region Illumina MiSeq sequencing was used to characterize bacterial(cell diameter is less than 0.2um) community structure dynamics with high taxonomic resolution in this study.

Findings
This high-throughput sequencing analysis produced 2365844 clean reads, which comprised 6334 OTUs. The mesocosm bloom significantly changed the bacterial community structure. Initially, all mesocosms were dominated by proteobacteria. Bacteriodete is stimulated by mesocosm bloom later on. Finally, cyanobacteria was the predominant class in the all mesocosms. However, no significant differences between high CO2 treatment and low CO2 treatment were observed in bacterial abundance, community assemblage and composition.

Conclusions
The results demonstrate that marine bacterial community are highly resistant to elevated CO2 and lower pH conditions in subtropical coastal seawater. It is tempting to conclude that there are no direct effects on marine bacterial communities imposed by ocean acidification because marine bacteria in subtropical coastal region hold enough flexibility and capacity to deal with future carbonate system changes caused by elevated CO2 and subsequent ocean acidification.