Offshore Seafloor 313 Nankai Trough from Suruga bay to Kyushu waters

Basic Information References

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Characteristics References

These waters extend from the east side of Suruga Bay to the Nankai Trough, which drops sharply from the coast all the way to southern Kyushu. Waters that deepen suddenly extend from the coast of Cape Omaezaki to the Kii Peninsula (to the south of Cape Ashizuri), reaching a difference in elevation of 1800 m and a total length of 670 km (Tokuyama et al, 2001). It includes many submarine short canyons (Japan Coast Guard, Hydrographic and Oceanographic Department, 1985).
The V-shaped submarine canyon with depths of 2000 m that runs through the middle of Suruga Bay (the Suruga Trough) separates the Eurasia Plate to the north from the Philippine Sea Plate to the south. On the east side of these waters is a bank called Senoumi where Calyptogena kawamurai have been discovered, suggesting the presence of a community of chemotrophs (Fujikura et al, 2008).
As a boundary between plates, the Nankai Trough is predicted to be the epicenter of a massive earthquake. These waters have been confirmed to be home to the greatest number of seep communities, and here from Kinsunose (off Cape Omaezaki to the south) to the waters 4800 m deep offshore from the coast of Cape Muroto, seep communities have been discovered in numbers unrivaled worldwide. Also here are highly diverse species of bivalves in the family Vesicomyidae, with at least 12 species discovered thus far. At Kinshunose, Mesolinga soliditesta, Bathymodiolus aduloides, and others have been discovered, leading to speculation that there are active methane seeps here. The presence of a bottom simulating reflector (BSR) has been confirmed in this area as well, and it is thought that there is a methane hydrate layer here (Fujikura et al., 2008).
In the Tenryu Canyon that cuts across the Nankai Trough, diverse species have been reported, including not only those specific to seep communities but also many species that depend on photosynthesis, and invasive species as well. The Kumano Basin in the southern Kumano Sea is home to seven mud volcanoes. BSRs have been confirmed in the seabottom called Kumano Knolls Nos. 1-7 as well, and these waters are habitat for Calyptogena fausta, Vesicomya crenulomarginata, Calyptogena (Archivesica) similaris, and others. Seep communities are found at Muroto Knoll off Cape Muroto as well, and Vesicomya kaikoae are distributed here. Species of tubeworm have been confirmed at Ashizuri Knoll of Cape Ashizuri (Fujikura et al, 2008).
Numerous species of precious corals are distributed offshore from Cape Ashizuri and Cape Muroto (Iwasaki, 2008), making this a coral fishing grounds. The waters of the Kumano Sea and off the shore of Tosa are high in biodiversity in terms of fish species as well (Kimura, personal communication).