LONG-TERM OBSERVATION OF DEEP-SEA BENTHIC ACTIVITIES IN SAGAMI BAY, CENTRAL JAPAN Hiroshi Kitazato (1) , Katsunori Fujikura (2) , Yasuo Furushima (3) , Takashi Toyofuku (4) , Hidetaka Nomaki (5) , Ryoichi Iwase (6) (1) Institute of Biogeosciences, Japan Agency for Marine-Earth Science and Technology, 2-15 Natsushimacho, Yokosuka 237-0061, JAPAN, Email: kitazatoh@jamstec.go.jp (2) ibid, Email: fujikura@jamstec.go.jp , (3) ibid, Email: furus@jamstec.go.jp , (4) ibid, Email: toyofuku@jamstec.go.jp , (5) ibid, Email: nomakih@jamstec.go.jp , (6) ibid, Email: iwaser@jamstec.go.jp ABSTRACT Sagami Bay locates at the central Japan facing to the Pacific Ocean. Deep trough, called Sagami Trough, that show more than 1500 m deep lines at the central part of the Bay. Sagami Trough is convergent plate boundary between North American Plate and Philippine Sea Plate. Epicenter of huge earthquakes and active submarine volcanoes are located at the western part of the Bay. A lot of cold seepages with Calyptogena- clam colonies are distributed in the bay. JAMSTEC has long been monitoring crustal movement at the deep-sea floor. There is a long-term deep-sea observatory at the Off Hatsushima Island site at the western part of the bay. Since 1993, JAMSTEC continuously monitor benthic activities at the permanent observatory. We could pile up time-series video records and environmental dataset. Through these dataset we can trace environmental changes at continental slope regions and also watch how deep-sea benthic organisms actively dwell at deep-sea floor in relation to environmental changes. We also keep permanent deep-sea station at central Sagami Bay for monitoring long-term changes in population ecology of deep-sea meiofauna since 1991. Using these dataset, we can evaluate deep-sea environmental changes and responses of deep-sea organisms against environmental changes. We believe that human impact has already started to affect even at deep-sea floor. We propose to continue monitoring of deep-sea environments and organisms in Sagami Bay with several innovative approaches. Continual environmental monitoring through cable network at deep-sea observatory of the Off Hatsushima Island site, frequent ROV and AUV observational dives are strong tools for getting deep-sea data in Sagami Bay. 1. INTRODUCTION The deep-sea floor is one of the most important environments on Earth. In particular, deep-sea sediments, the sediment-water interface (SWI) and the benthic ecosystems these environments support play a key role in global biogeochemical cycling and act as a vital mechanism for particulate and dissolved organic carbon storage in deep-sea sediments. However, little is known about the role of deep-sea ecosystems, in particular at the SWI at the global level and still less on the importance of biodiversity on ecosystem functioning in deep-sea ecosystems. Key unresolved questions include how do anthropogenic influences and inputs reach the deep-sea and affect ecosystem functioning? What role do deep-sea organisms play in deep-sea biogeochemical cycling? Long-term observations and monitoring of the biodiversity, structure, function and dynamics of deep-sea ecosystems at fixed or mobile stations to resolve these questions. Figure 1. Long-term monitoring areas at Sagami bay, Japan, and schematic figures of cable network monitoring systems and frequent observation by research vessels.