Bubble-mediated transport of benthic microorganisms into the water column: Identification of methanotrophs and implication of seepage intensity on transport efficiency

Sebastian F A Jordan,Ira Leifer,Heide Schulz-Vogt,Oliver Schmale,Tina Treude,René Janßen,Johannes Werner

doi:10.1038/s41598-020-61446-9

Abstract

Benthic microorganisms transported into the water column potentially influence biogeochemical cycles and the pelagic food web structure. In the present study six gas-releasing vent sites in the Coal Oil Point seep field (California) were investigated, and the dislocation of microorganisms from the sediment into the water column via gas bubbles released from the seabed was documented. It was found that the methanotrophs transport efficiency was dependent on the volumetric gas flow, with the highest transport rate of 22.7 × 103 cells mLgas−1 at a volumetric gas flow of 0.07 mLgas s−1, and the lowest rate of 0.2 × 103 cells mLgas−1 at a gas flow of 2.2 mLgas s−1. A simple budget approach showed that this bubble-mediated transport has the potential to maintain a relevant part of the water-column methanotrophs in the seep field. The bubble-mediated link between the benthic and pelagic environment was further supported by genetic analyses, indicating a transportation of methanotrophs of the family Methylomonaceae and oil degrading bacteria of the genus Cycloclasticus from the sediment into the water column. These findings demonstrate that the bubble-mediated transport of microorganisms influences the pelagic microbial abundance and community composition at gas-releasing seep sites.

Highlights

Benthic microorganisms transported into the water column potentially influence biogeochemical cycles and the pelagic food web structure
Bacteria located at shallow sediment depths can be mobilized by infiltrating seawater and carried to deeper sediment strata, from where they can be injected into the water column by submarine groundwater discharge[3]
Gas bubble emissions generally were more vigorous at IV Super Seep than at Rostocker Seep

Summary

Introduction

Benthic microorganisms transported into the water column potentially influence biogeochemical cycles and the pelagic food web structure. The bubble-mediated link between the benthic and pelagic environment was further supported by genetic analyses, indicating a transportation of methanotrophs of the family Methylomonaceae and oil degrading bacteria of the genus Cycloclasticus from the sediment into the water column These findings demonstrate that the bubble-mediated transport of microorganisms influences the pelagic microbial abundance and community composition at gasreleasing seep sites. The factors controlling bubble-mediated transport were unknown, Schmale et al.[7] hypothesized that transported MOB can inoculate overlaying waters, thereby enhancing the efficiency of the pelagic methane sink In this detailed mechanistic study, we conducted a series of bubble-catcher experiments at two different seep sites to assess the influence of the parameters seep intensity, bubble size distribution, and vent density on the efficiency of the bubble-mediated transport of benthic microorganism into the water column. A simple budget calculation was applied to assess the impact of the Bubble Transport Mechanism on the water column MOB abundance above the Coal Oil Point (COP) seep field

Methods

Results

Conclusion