Although more than 80 percent of earthquakes in Japan occur on the seafloor, seismic network on the seafloor is quite few and insufficient. As a step to increase seafloor seismic network, Comprehensive Seafloor Monitoring System was deployed in Nankai Trough off Cape Muroto in March 1997. The prototype system is a combination of observatories with a cable and without a cable. The former system comprises of two seismometers, two Tsunami pressure gauges, seafloor observatory with multiple sensors and 125 km long optical cable. The data are sent in realtime to the land station at Muroto and they are also transmitted to JAMSTEC in Yokosuka and Meteorological Agency of Japan. The latter system, which could be deployed at any place, comprises of seafloor observatory with imultiple sensors and four long-term digital ocean bottom seismometers. The data could be recovered once every month by releasing pop-up buoys to the surface through the satellite. The system with a cable was deployed on the land ward slope of Nankai Trough off Muroto at water depths between 1286 m and 3572 m. The system without cable will be deployed 200 km off Muroto in Shikoku Basin at a depth of 4300 m in early 1998. Five similar systems will be deployed until the year of 2002.

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Since the establishment of JAMSTEC in 1971, several basic and advanced survey systems have been developed to exploit and study the deep ocean. Presently, 4000-m and 6000-m deep tow systems, 2000-m and 6000-m manned submersibles, 3000-m, 7000-m and 10000-m ROVs, and cabled deep seafloor observatories are in operation. A deep and long range AUV to survey under the ice or hazardous environment, and a wire line reentry system to study crustal deformation process are under development. In addition to the above survey systems, the five-vessel JAMSTEC fleet, R/V Natsushima, Kaiyo, Yokosuka, Kairei and Mirai supports research activities in all of the world’s oceans. The operating principle for research at JAMSTEC in the next decade is “in depth understanding of the Earth and life”.We will further expand research activities by utilizing basic and advanced systems, and deep ocean technology to achieve the above goal.

Abstract. Abyssal microfloral succession induced by experimental organic degradation was investigated. Notable changes in amounts and compositions of short‐chain (C9‐20) sediment fatty acids were observed, which indicated the shift of sediment microflora. Biomarker fatty acids for methanotrophs and sulfate‐reducing bacteria dominated. Resultant fatty acid compositions were most closely related to those from a nearby methane seep harboring a dense Calyptogena colony; the clams were also seen in close vicinity of the deployed organic mass. These observations suggest that the organic degradation on the bathyal seafloor stimulates the formation of methanotrophic and thio­trophic microflora, resulting in the formation of a methane‐seep‐type benthic community.