Offshore Seafloor 308 Sagami Trough and ssouthern seamounts of Izu-Ogasawara Arc

Basic Information References

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Characteristics References

These waters include the Tokyo Canyon and the submarine canyons that drop steeply from Sagami and Suruga Bays as well as the Sagami Trough, spanning 330 km between Sagami Bay, the Boso Peninsula, and Ohshima, and extend to the south to Myojin-sho, the Suiyo Seamount, the Mokuyo Seamount, and the Kaikata Seamount of Izu-Ogasawara Arc.
The east side of the Sagami Trough in Sagami Bay is lined with the Okinoyama Bank Chain, the Misaki Knoll, the Miura Knoll, and the Sagami Knoll. Numerous chemosynthetic community have been confirmed in Sagami Bay (Fujikura et al, 2008). The boundaries of three plates come together in the Sagami Trough southeast of the Boso Peninsula. Here the terrain and structure of the sea floor is complex, reflecting the interactions of these plates, and there are numerous major earthquakes and volcanoes (Japan Oceanographic Data Center, 1985). The slope of the submarine canyon in Suruga Bay is very rich in biodiversity (Kimura, personal communication), and these are unique waters inhabited by a large number of creatures (Nonaka and Iwahashi, 1987; Misawa et al., 2007; Mukai and Haseyama, 1976). In the vicinity live many Japanese spider crabs, a species endemic to Japan (Nonaka and Iwahashi, 1987; Misawa et al., 2007; Mukai and Haseyama, 1976). The Myojin Knoll is a site of large-scale hydrothermal activity, with chemosynthetic community formed around hydrothermal vents, including Gandalfus yunohana, シチヨウシンカイヒバリガイ and others (Fujikura et al., 2008). Suiyo and Mokuyo seamounts also have hydrothermal vent activity on their caldera floors, with シチヨウシンカイヒバリガイ, Alvinocaris brevitelsonis and other species living near the vents (Fujikura et al., 2008). Hydrothermal vent activity also has been discovered at Kaikata Seamount, a volcano on the sea floor, and species including オオマユガイ, Shinkailepadidae and others have been confirmed here (Fujikura et al, 2008).
These waters, up to roughly 800m in depth on the Choshi Coast, are home to numerous shellfish species, including Fulgoraria (Nipponomelon) elongata, thought to be endemic to these waters (Okutani, 2000).