Bubble-mediated transport of benthic microorganisms into the water column at methane releasing seep sites (Coal Oil Point Seep field): Identification of methanotrophs and implication of seepage intensity on transport efficiency

In aquatic habitats, the water column and underlying sediment are strongly connected by several exchange processes. It is assumed that benthic microorganisms transported into the water column influence biogeochemical cycles and the pelagic food web. Recent studies at the Coal Oil Point seep field (California) discovered a new bubble-mediated transport mechanism, which transfers methanotrophs from sediments into the water column.

In our present study, we focused on the parametrization of the bubble-mediated transport mechanism and identified the methanotrophic bacteria transported into the water column by bubbles released from the seabed. Bubble-catching experiments under different gas seepage intensities were conducted at the Coal Oil Point seep field. By applying molecular biological methods, we were able to show that the transport efficiency of microbial cells at gas vents is dependent on the gas seepage intensity. We further identified eight OTUs (operational taxonomic units), assigned to the methanotrophic family Methylomonaceae, that were transported by the gas bubbles from the sediment into the water column. These OTUs are potential inoculants of the water column and may contribute to the local pelagic methane sink at gas-bubble-releasing seep sites. In addition to the studies conducted offshore California, we performed field studies at the North Sea blowout site. Here, we used a combination of oceanographic current measurements and quantification of methanotrophs along two water column transects to determine the contribution of the bubble transport to the local abundance of methanotrophs and to assess the impact of this transport process on the pelagic methane sink.