Minor impact of ocean acidification to the composition of the active microbial community in an A rctic sediment

Summary Effects of ocean acidification on the composition of the active bacterial and archaeal community within A rctic surface sediment was analysed in detail using 16S rRNA 454 pyrosequencing. Intact sediment cores were collected and exposed to one of five different pCO 2 concentrations [380 (present day), 540, 750, 1120 and 3000 μatm] and RNA extracted after a period of 14 days exposure. Measurements of diversity and multivariate similarity indicated very little difference between pCO 2 treatments. Only when the highest and lowest pCO 2 treatments were compared were significant differences evident, namely increases in the abundance of operational taxonomic units most closely related to the H alobacteria and differences to the presence/absence structure of the P lanctomycetes . The relative abundance of members of the classes P lanctomycetacia and N itrospira increased with increasing pCO 2 concentration, indicating that these groups may be able to take advantage of changing pH or pCO 2 conditions. The modest response of the active microbial communities associated with these sediments may be due to the low and fluctuating pore‐water pH already experienced by sediment microbes, a result of the pH buffering capacity of marine sediments, or due to currently unknown factors. Further research is required to fully understand the impact of elevated CO 2 on sediment physicochemical parameters, biogeochemistry and microbial community dynamics.