Effect of elevated CO2 on the dynamics of particle-attached and free-living bacterioplankton communities in an Arctic fjord.

In the frame of the European Project on Ocean Acidification (EPOCA), the response of an Arctic pelagic community (<3mm) to a gradient of seawater pCO₂ was investigated. For this purpose 9 large-scale in situ mesocosms were deployed in Kongsfjorden, Svalbard (78°56.2' N, 11°53.6' E), in 2010. The present study investigates effects on the communities of particle-attached (PA; >3 µm) and free-living (FL; <3 µm>0.2 µm) bacteria by Automated Ribosomal Intergenic Spacer Analysis (ARISA) in 6 of the mesocosms, ranging from 185 to 1050 µatm initial pCO₂, and the surrounding fjord. ARISA was able to resolve, on average, 27 bacterial band classes per sample and allowed for a detailed investigation of the explicit richness and diversity. Both, the PA and the FL bacterioplankton community exhibited a strong temporal development, which was driven mainly by temperature and phytoplankton development. In response to the breakdown of a picophytoplankton bloom, numbers of ARISA band classes in the PA community were reduced at low and medium CO₂ (~185-685 µatm) by about 25%, while they were more or less stable at high CO₂ (~820-1050 µatm). We hypothesise that enhanced viral lysis and enhanced availability of organic substrates at high CO₂ resulted in a more diverse PA bacterial community in the post-bloom phase. Despite lower cell numbers and extracellular enzyme activities in the post-bloom phase, bacterial protein production was enhanced in high CO₂ mesocosms, suggesting a positive effect of community richness on this function and on carbon cycling by bacteria. [ABSTRACT FROM AUTHOR]