[M-IS26] Gas hydrates in environmental-resource sciences

[MIS26-06] Characterization of the benthic community in surface sediments in a shallow gas hydrate reserve area off Sakata, eastern margin of the Japan Sea

*Yuki Ota¹, Ryo Mukai², Tomo Aoyagi¹, Tomoyuki Hori¹, Akira Iguchi¹, Miyuki Nishijima¹, Atsushi Suzuki¹, Masahiro Suzumura¹ (1.National Institute of Advanced Industrial Science and Technology, 2.Marine Biological Research Institute of Japan Co., Ltd.)

Keywords:marine sediment, methane hydrate, benthic community, environmental DNA, carbon and nitrogen isotope, Japan Sea

Marine methane hydrate has been widely considered as a future energy resource supply. Environmental impact assessment is the prerequisite for development of natural methane hydrate resources, and the correct understanding of the characteristics of benthic organisms is the basis for such assessment. To discuss the effect of local upward methane diffusion on the benthic community structure, we collected benthic organisms and sediment core samples inside microbial mat indicating methane seepage and at the reference site in a shallow gas hydrate reserve area in a knoll off Sakata, called Sakata Knoll, the eastern margin of the Japan Sea. The collected sediment samples were used to analyze environmental DNA metabarcoding targeting 16S and 18S rRNA and the organic matter C and N isotopic compositions. The results of these analyses showed a high relative abundance of annelids, which mainly consisted of Dorvilleidae and Ampharetidae, at the site inside microbial mat. Sulfur-oxidizing bacteria and aerobic methanotrophs that seem to feed these annelids mainly compose the microbial population of the microbial mat in Sakata Knoll. The results of organic matter carbon and nitrogen isotopic compositions indicated the biological community with methane-derived negative carbon isotopic signatures (–30 to –45‰ VPDB) in the sediment inside microbial mat. It therefore appears that the microbial mat caused by methane seepage contributes as the diet to the unique annelid community in Sakata Knoll. In the future works, it is important to investigate the signature of isotopic compositions in the organisms living in Sakata Knoll to further understand the structure and food web architecture of benthic community. This study was conducted as a part of the methane hydrate research project funded by METI (Ministry of Economy, Trade and Industry, Japan).