Offshore Seafloor 321 Naisei-shoto Islands, Okinawa Trough

Basic Information References

Reason(s) for selection Criteria

Characteristics References

These waters make up part of the Nansei-shoto Islands and Okinawa Trough.
The Okinawa Trough is a back arc basin in which large cracks have been forming since roughly two million years ago as the continental crust splits. Hydrothermal vent communities have been found from the Minami-Ensei Knoll (150 km west of Amami-Ohshima) in the north to the Hatoma Knoll (northwest of Miyako Island) and Yonaguni Knoll No. 4 (northwest of Yonaguni Island) an others in the south, making it one of the big hydrothermal vent fields in the western Pacific (Fujikura et al., 2008). Megabenthos numbering 49 species have been confirmed at the Minami-Ensei Knoll, a large-scale hydrothermal area bristling with chimneys. Bathymodiolus, Paralomis jamsteci, Shinkaia crosnieri, and other species live around the chimneys. The hydrothermal vent area at Hatoma Knoll includes a chimney of hydrothermal solution more than 300°C in temperature, Shinkaia crosnieri, Alvinocaris longirostris, and Lepetodrilus nux. At Yonaguni Knoll No. 4 is a black smoker that emits pitch-black hydrothermal solution, and its biota resembles that of Hatoma Knoll. Numerous other hydrothermal vent communities have been confirmed in these waters as well (Fujikura et al, 2008).
In addition, distribution of precious coral has been confirmed in Hozan-sone area between Okinawa and Miyako Islands (Nonaka and Muzik, 2009; Suzuki, 1991).