231 George, R. Y. and S. D. Cairns, eds. 2007. Conservation and adaptive management of seamount and deep-sea coral ecosystems. Rosenstiel School of Marine and Atmospheric Science, University of Miami. Bathymetric distribution and biodiversity of cold-water octocorals (Coelenterata: Octocorallia) in Sagami Bay and adjacent waters of Japan Asako K. Matsumoto, Fumihito Iwase, Yukimitsu Imahara, and Hiroshi Namikawa Abstract in total, 260 octocoral species, including 144 gorgonians, 80 alcyonaceans, and 36 pennatulaceans have been recorded in the literature at Sagami Bay, Japan. Fifteen of the octocoral species were newly recorded at littoral to bathyal depths (13 gorgonians, one alcyonacean, and one pennatulacean). Thirty families of octocorals were recorded between the depth of 100–200 m (deep littoral) and 23% of all recorded species and 37% of newly recorded species were obtained at this depth. A total of 114 species of octocoral is endemic to Japan and adjacent waters, while 74 of these octocorals are only found in or around Sagami Bay. These results reconirmed the high biodiversity of octocoral fauna in Sagami Bay, and suggest there are two main explanations for these high levels of biodiversity in this bay and in this area. One explanation appears to be that the recorded species represent a faunal boundary which is formed by converging elements of temperate, sub-tropical, and sub-arctic regions. Another explanation may be that the 100–200 m depth range may be a benthic/pelagic ecotone, a transitional zone between two ecosystems, which results in a high degree of biodiversity due to benthic- pelagic coupling. Sagami Bay (approximately 33–35°N and 138–140°E), located near Tokyo, has played very important roles historically, commercially, and culturally for Japan (Fig. 1A). The sea bottom in the area is composed of the North American Plate and Philippine Sea Plate and has very complicated geographical features. Research on octocoral (Coelenter- ata: Octocorallia) fauna in Sagami Bay began in 1868 with a report on the gorgonian coral Acanella gregori by Gray collected from Enoshima by B. Gregory, the surgeon onboard the H.M.S. Rattler (Imahara, 2006). Since then, several studies on octocoral biodiversity in Sagami Bay have been conducted, including many expeditions such as those of the Challenger, Tiefsee, Albatross, and Sixten Bock, the research by Döderlain, Doflein, Mortensen, Japanese emperor Hirohito (Isono, 1988; Fujita and Namikawa, 2003; Takeda et al., 2006), reported by Holm (1894), May (1899), Mo- roff (1902), Kishinouye (1903), Kükenthal (1906, 1909), Kinoshita (1908, 1909, 1913), Kükenthal and Gorzawsky (1908b), Balss (1910), Kükenthal and Broch (1911), Nutting (1912), Okubo (1929), Thomson and Rennet (1929), Kumano (1937), Utinomi (1952, 1955, 1962), Suzuki (1971), and Utinomi and Imahara (1976) (see additional references in Imahara, 1996, 2006; Iwase and Matsumoto, 2006).